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MG Midget and Sprite Technical - Suspension Bottoming?
| Semic elliptics; Front Line telescopics and lowered rear suspension. With two up I am getting a hefty clonk over certain bumps. Nothing is loose and it doesn't happen one-up so I'm wondering whether the rubber stops are banging home. The problem with lowered suspension must be much less distance to travel before bottoming without initially placing more preload on the spring.
Would stiffening the shocker settings help; are stronger springs needed? Presumably removing the lowering blocks should solve it. Any suggestions please. |
| Graeme Williams |
| You could try cutting down the bump rubbers. |
| Dave O'Neill 2 |
| If you increase the bump damping you may find your suspension pumping up on rougher roads. Of course you might not, so probably worth a try. |
| Greybeard |
| Check that the shocks aren't bottoming out as IIRC they don't have bump rubbers in them, compare their travel to the gap between the bump stop and upper plinth and assume the bump stop compresses to around 1/2 original height. The later 1/2 elliptic bump stops are fairly compliant IMO and I fitted them to my frogeye in preference to the original early rubber bricks for a better transition when they came into play. |
| David Billington |
| Are you sure it's not the shocks bottoming out? The bump stops wouldn't clunk, thud maybe! It's difficult to get vertical tube shocks to work without bottoming out, especially when lowered. |
| John Payne |
| If the shocks are bottoming the solution is usually to invert the lower spring plates. This involves swapping them over, side to side and results in lowering the bottom end of the shock mounting point which increases the available travel for the shock tube by about 1" But maybe the Frontline system uses a different arrangement for fitting? |
| GuyW |
| THe bottoming noise is a very solid bang, like a large hammer. I've wedged a small rubber "plug" in the hollow end of the bump stops. If it bottoms out that will be knocked down into the main stop and act as a tell-tale. |
| Graeme Williams |
| IIRC the Spax kit 1/2 elliptic kits required that the lower damper plates were swapped from one side to the other and turned upside down to get the correct position to stop the dampers bottoming out. The FL damper being more upright had new lower bottom mounts with extra holes to allow for extended travel to prevent the same problem. Graeme, What is fitted to your car and any pics of the set-up. |
| David Billington |
| Frontline RS2 I will check the max/min length and compare that with the installation. I would have thought that if the dampers were bottoming there was a chance the brackets would show a bit of distortion. |
| Graeme Williams |
| Mightn't have got that far yet Graeme The bottom plates are usually swapped for tube shockers so that the brackets hang downwards as Guy and David have mentioned Which way are yours Also does your exhaust go over or under the axle, If it's over it could be hitting |
| William Revit |
| The other possibility is that different brands of tubular shocks have different max/ min travel. If yours have been renewed from the original Frontline ones this could cause problems. |
| GuyW |
| I'll disconnect a shocker this morning and see how much stroke it has. Interestingly, it get worse after drivng for awhile- perhaps that's linked with the oil warming up and reducing their effectiveness. The exhaust goes under the axle, William. |
| Graeme Williams |
| Graeme, if you measure the clearance between the bump stop rubber and the plinth that it strikes on, with the car loaded, you will get an idea of how much the shock tube needs to compress from its normal at rest position. Given that the rubber of the bump stop will also compress slightly, you need to have slightly more available movement in the shock tube than that clearance. |
| GuyW |
| This is from the RS2 fitting instruction for 1275 semi-elliptical so there may be some variance.
"Measure the normal operating length of the damper. Now close the damper to its shortest length and calculate the difference between these two measurements. It should be at least 10mm greater than the distance between the axle bump stop and the body. - This allows some compression of the bump stop. - If it is less than this move the special machined bolts to the lower holes on the mounting brackets and check again." |
| Nigel Atkins |
| Well there you go Nigel. Just goes to show you cannot trust everything that you read in print. (They forget to say the axle to bump stop clearance has to be taken with the car laden, driver, passenger and luggage) |
| GuyW |
| Guy, I don't trust anything related to Frontline, I thought that would be understood, I just put up the published instructions from the makers/suppliers of the item. I expect they'd say their instruction cover the installation requirements. |
| Nigel Atkins |
| I don't think it matters whether the car is laden or not as you just need to verify the available damper travel exceeds the bump stop to plinth distance by a suitable amount to take into account the bump stop compression. |
| David Billington |
| The bit I've never understood for sure is - "Measure the normal operating length of the damper." What exactly should you measure and how?
Mine were fitted by a self acknowledged and promoted specialist expert company and to be fair these, unlike other work they carried out. have always seemed to have been fitted correctly and do the job (other than perhaps the range of the damper adjustment being far too bias to the harder settings). Off course me being me I got a damper that leaked IIRC just out of warranty but that's not their fault. |
| Nigel Atkins |
| And the prize goes to......... GuyW! Shockers are bottoming out. Only 35mm travel but the lower brackets are "mounting hole at the top" so I need to swap over sides and invert! The chap who built the car I suspect only used it on his own. I doesn't bottom out one up, so either i swap the brackets or tell Mrs she isn't coming out any more. Where's my spanner.......? |
| Graeme Williams |
| Careful how you word it when you tell Mrs Williams that the problem is to do with bottoming! |
| GuyW |
The later(?) kits have brackets with two mounting holes.
 |
| Nigel Atkins |
| Why does Guy get the prize when both myself and John Payne mentioned it before Guy. |
| David Billington |
| Yes, I was wondering that David! Maybe it's because we didn't mention turning the plates around. |
| John Payne |
| Yes, I had to bring in a third party to decide on what was a very close call. The mention of the plates requiring changing from side to side and turning over was a very full answer and just enough to get the decision.
After all, in the best tradition of answers here and on the MASC page of F/Book, you always ignore earlier posts and make the same point again later down the thread. However to everyone who took time out to answer I am grateful. I was focussed on the bump stops. My only slight concern now is the fact that unloaded, the shockers are pretty well fully extended. I hope that won't cause a problem on rebound but I couldn't see a way round that. Neither mountings have enough metal around to move them. It may be that Mike Sutton when he built the car was concerned about the "full extension" and inverted the brackets, not realising he had created a problem at the other end. |
| Graeme Williams |
| Graeme,
Maybe worth while working out the best position for the lower damper mount so it doesn't go solid but gives more downward travel. If the inverted plates sort the bump issue but give too little droop travel it can result in wheel lift on cornering even at low speed and loss of drive, I've encountered it with the Spax 1/4 elliptic conversion. The solution could be to put the plates back as original but space them down like a lowering block but in between the damper plate and spring rather the between spring and axle to get the best travel compromise, longer U bolts may be required. |
| David Billington |
| That's a good idea David. Where can I source the longer u-bolts? The ones I have are longer than standard anyway so would need to be longer again! |
| Graeme Williams |
| John, David. I never laid claim to any prize! But these things are usually part of an ongoing discussion and my post therefore started with "If they are bottoming out" as a direct reference and follow on to you both suggesting this might be the case. But neither of you gave any explanation why this might be happening, or the solution of inverting & switching the spring plates. Rarely does a full solution come from one person in a single post. :-) |
| GuyW |
| David, I am not convinced by that last point of yours! Using spacers may give more accurate positioning and finess over the relative position of the lower eye of the shock than inverting the spring plates does, and maybe that is what you are meaning? But other than that it makes no difference to the available 'droop' travel of the shock whether this is achieved by using a spacer or by inverting the plate. Either has the same effect in lowering the eye relative to the axle and bump stop platform. |
| GuyW |
| Guy,
Looking at the "Rear suspension duck noise" thread image of the standard damper plate I would estimate inverting it would drop the lower pick-up by around 1.5" - 1.75". If you only needed to drop the lower damper pick-up by 1" to stop the dampers going solid and you moved it down 1.75" then you would lose 0.75" of available droop travel which is significant, I'm assuming the dampers have the same travel as governed by the standard bump stop and check strap. Spacers should be easy to make from readily available aluminiun section with some simple drilling to take the U bolts and centre spring bolt head. |
| David Billington |
| Yes David, that is what I meant. I think we are agreeing, arn't we? <<Using spacers may give more accurate positioning and finess over the relative position of the lower eye of the shock than inverting the spring plates does, and maybe that is what you are meaning?>> More precise than inverting the plates, but otherwise the same effect. |
| GuyW |
| As I said earlier it's difficult to get a vertical tube shock conversion that doesn't bottom or top out due to the lack of stroke of the shocks that are short enough to fit. On my first attempt they used to top out and lift the inside wheel on hard cornering. In the end I used much longer shocks on the standard Spring plates but had to weld small turrets in. That way I could use normal shock top mounts instead of bolt and eye type.
I know the Spax kit isn't supposed to be as good as the Frontline one but because it isn't vertical it doesn't have the same problem of bottoming out. |
| John Payne |
| Like a lot of things, this all becomes clearer as you get into it.
I can see exactly what John Payne means now. When I took measurements of the original installation I only had about 25mm of movement before the shocker would bottom out, but the gap between the bump stop and "the hard bit" was 45mm. So turning the bracket up the other way didn't seem excessive (didnt measure the extra it gave because according to the installation sheet it should be that way). However now the restriction is going to be at the other end - "topping out" I suppose it's called. I don't know whether there will be enough body roll to cause the wheel to lift. I tried jacking under the front end of the spring on one side and the weight started to come off the wheel pretty soon. Whether that was the spring on it's own lifting it or it's being pulled up by the damper I don't know. Spacing an inverted bracket down may give a better compromise but it looks like I will need around 20/25mm of packing so that will require a full blown spacing plate. Perhaps the original builder disnt just get the plate up side dwon but made a decision between bottoming and topping and decided the former was less of a problem (and for one off it isn't). Perhaps a bag of cement in the boot? |
| Graeme Williams |
| Does anyone know what the spec is for theses dampers? I have asked Frontline what the stroke is and got no response to my email. I think the suspension being lowered helps not hinders. I only need the bumper/chassis gap plus a safety marking (F/L say 10mm on the compression), say my 45 +10 +10. That's not much but it seems a struggle to get it right. |
| Graeme Williams |
| If its any help i've Spax on my chrome bumper (semi eliptical) and I've just checked the Archive where I posted details of the units :- 260/265mm closed C/C 380/385 extended C/C. There are other posts regarding dims of mini shocks etc R. |
| richard b |
| My set up uses the top mount for the rebound straps, reinforced, as the top position for the shock. The lower point is the inverted spring plate. The units I used are Mini front shocks and are mounted pretty well vertically. In setting this up the first ones I bought didn't have sufficient travel. I couldn't find that sweet spot where they didn't either bottom out or clunk on lift. I then looked through specifications from different suppliers and eventually found others, though still specified for minis, that gave a better stroke length that worked.
On balance, for road use at least I find it more important that they don't bottom out. Suspension bottoming out is a far more common feature of driving for me than is the puddlejumper feature generally only experienced on humpback bridges. |
| GuyW |
| I have found a spec sheet for AVO dampers so I'll try to find which are my units and then compare. I'll also talk to F/L tomorrow. |
| Graeme Williams |
| Graeme,
forget FL (they must have been very busy coaching 5 guys tonight to avoid giving answers) contact AVO instead as IIRC FL cleverly have the dampers on "contract" so officially they might be classed as not on usual stock information - but do see if you can get model numbers for the FL dampers, use your charm, wit and guile. Telephone: 01604 708101 If they still employ anyone called Nigel they must be a good, friendly and approachable company to deal with (if not always over-optimistic). I note on their lists - "Open lengths are taken from loop centre to loop centre, Closed lengths are quoted metal to metal. All units have an 1" bump stop therefore closed length will increase by 1"." |
| Nigel Atkins |
| Thinking about it overnight, I'm going to strip it out again and take all the measurements and see if a sweet spot as Guy refers to it, can be achieved. |
| Graeme Williams |
| My first attempt used Mini fronts, the longer ones I use now are Mini rears. (｣10!) Demon Tweeks do a range of adjustable shocks with different lengths and strokes. They also do them with ally bodies. I知 probably going to upgrade mine to a pair of them at some point. I致e got the dimensions of my shocks written on the garage wall somewhere - I値l have a look tonight. |
| John Payne |
| John, I though Mini rears had the wrong attachment design at the top? A stud /pin rather than an eye. Or have you mounted yours through a reinforced plate in the floor.
With vertical shocks, they take the place of the usual rubber axle drop strap, and I suppose as long as their extended length is the same or longer than the straps (allowing for spring plate inversion) then they won't cause wheel lift any more than the rubber straps do. As they are vertical when mounted this way, the measurements and calculations for min and max shock movement are pretty simple. But if mounted using a Spax or similar kit then don't they operate at an angle? The extension/ compression travel of the shock tube needs to be greater than the vertical axle movement calculations. You could consult Pythagoras over this as I believe he had angled shocks fitted to his chariot and worked out a formula for calculating the required lengths. |
| GuyW |
| Guy: Pythagorus kept his chariot concours so he had lever arm. I'll draw it out (no not the chariot). Thinking about packing the bracket and wodering, if I resort to this, whether a lamp of nylon or similar would suffice. Probably going to be about 18mm thick and I envisage a block the same plan profile as the bracket. |
| Graeme Williams |
| I'm not sure of that Guy, I'm no Pythagorarian but surely if they are angled they won't need as much travel? But as usual I could be wrong!
Yes, the Mini rears have a the other type of mount, which mount in small turrets welded in the floor just forward of the cockpit/boot divider. I've found my cave writing on the garage wall and I'd worked out I needed 5 3/4 shock stroke when I did the conversion. It's a pity it needs some welding or it would be a cheap and easy conversion. Obviously most owners wouldn't want to be cutting holes in the floor and welding bit in. |
| John Payne |
| No John, if they are angled, say at 45 degs, then they need a longer travel to match the vertical movement of the axle. Draw it out as an inverted right angled vector triangle to see how this works. |
| GuyW |
| John, I agree the angle the Spax unit are fitted at will result in a reduced travel requirement for the damper, the maximum travel requirement will be for a damper fitted upright. The extreme situation would be a horizontal damper which would hardly need any travel but wouldn't be very effective. |
| David Billington |
| Guy, I知 doing just what you said to my car. I知 going to use Mini shortened Spax shocks mounted to the Axle check strap mounts and Magic midget lowered rear springs. Hopefully there値l be sufficient travel for fast road driving. |
| Kurt Barker |
| Taken measurements!
With the F/line bracket the designed way up I have 5mm of available drop on the axle, but when the bump stops hit I have 17mm further movement before the damper bottoms out. THis of course is unusable as the bump stop is fully home. Turning the bracket the other way up (which is how it was on my car), there is about 48mm available to drop the axle below its running position (excessive) but the damper bottoms out 23mm before the bump stop hits top. Hence the problem I am experiencing. So, rubbish either way. The sweet spot is obviously in between and is about 25mm below the higher position or 19mm above the lower. I could achieve this by dropping the bracket (in it's original orientation not the F/line way round) with 25mm packing but this means extended U bolts and they are overlong now because of the lowered ride. Can't find any. Alternatively I will have to chop the existing brackets about to reposition the damper mounting hole. Unless anyone has any other suggestions? |
| Graeme Williams |
| Kurt, just be aware that the top check strap mounting will probably need strengthening in order to take the extra load. They are designed for a fairly infrequent snatch from the rubber check strap, not the continual pounding from a tube shock.when I fitted mine they lasted a couple of years but eventually needed some extra welding between the triangular support plate and the floor.
David, John. I am still puzzling over this! Travel along the hypotenuse has got to be longer than on the adjacent side. The only thing l can think is that the axle doesn't move in a straight line, but an arc though that then becomes very complex if the curve of the spring flattens and lengthens under load and that would move the axle rearwards. And then, what if you have anti tramp bars fitted! Too early in the day for brain exercise! |
| GuyW |
| Gents
I also run Mini rear dampers (Kyaba GasAdjust) they were the ones with most closed -open travel IIRC its about 5.5" .....I have the exact numbers somewhere I can look them out if anybody wants them. I made up some adaptor blocks for the top pin mounts they are shown in the attached photo and attach into the check strap space, although the check strap was always fitted inside the axle tunnel on a long through bolt on 73 RWA. I was running the Frontline rears but never liked the fact that they don't have anything like enough travel and bottomed out what ever combination I tried , IIRC the rear suspension on my car has about 5.25" of travel and now I can achieve that with these dampers , and the check straps have been reinstated which makes me happy. I have never needed to strengthen the top mountings in the chassis, been running telescopic dampers in that position for about 15 yrs. Ian  |
| Ian Webb 1973 GAN5 |
Bottom mount
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| Ian Webb 1973 GAN5 |
Rear damper complete
 |
| Ian Webb 1973 GAN5 |
| Hi Ian, I'm glad you put you've not had to strengthen the top mountings as my FL kit still hangs off the strap brackets. As you know there's no way I'd defend FL's wrong doings but I don't think I've had problems with bottoming out of the rear damper kit that they supplied and installed (problem with their front kit and problems with them and many, many problems with their 5-speed conversion and installation). |
| Nigel Atkins |
| This is the damper I used as in the photo : Kayaba Gas A Just. Part No 552019 Extended: 368mm / 14.5" Closed: 222mm / 8.75" Stroke: 146mm / 5.75" Pin + Eye Supplier: Mini Spares Cost ｣29 ea Frontline Type AVO Midget CD430 kit Extended: 352 / 13.8" Closed: 250 / 9.8" Stroke: 102 / 4.0" TOO SHORT eye(special offset) + eye Ian |
| Ian Webb 1973 GAN5 |
| Guy, I've mocked up the damper being upright and inclined to demonstrate the reduction in required travel due to inclining the damper. The damper has 368mm extended length (14.5") and 127mm (5") travel as an example. The same damper is then inclined by 40 degrees and attached to the same points 127mm vertically apart to indicate the travel extremes as would be the case on the axle and a fixed top mounting. It reduces the damper travel from 127mm to 85.2mm.  |
| David Billington |
| Impressive drawing David! Seems a lot of effort to go to to prove me wrong - it usully is much easier than that! ;-) But seriously, thanks for the visual explanation. Acceptng then that the vertical mounting, as mine is, has a longer travel, does this then make them relatively stiffer as well, assuming like for like units? Longer travel means moving more oil? |
| GuyW |
| Don't know whether this will be readable (or comprehendable)! These are my measurements showing the two bracket positions (standard and inverted) and then both repositioned as if the suspension is against the stops. THe open and closed lengths are 352 and 245 and the suspension movement is 87mm approx from sitting on wheels unloaded to fully compressed.
My conclusion is that Guy's "sweet spot" as he describes it is almost mid way between the hole position with the bracket one way up and the hole position with it inverted.  |
| Graeme Williams |
| Graeme, if there is some compromise needed, then I would err towards giving adequate clearance on bottoming and be less concerned about full suspension droop. The reason is that on undulating roads and speed bumps the car will squat down onto the bump stops far more often than taking off. I also think there is more energy in downwards movement onto the stops, than in upwards movement when lifting off. |
| GuyW |
| Ian, that's a very neat solution. You could market it, especially as you have proved it to be better than Frontline's option. No welding required like mine and a huge choice of shocks from dirt cheap std replacement to top quality adjustable. Guy, by my reckoning the same rated vertical shock will feel stiffer than an angled one. |
| John Payne |
| Guy: totally agree. While looking at this I realised the potential damage to the sheet metal at the top of the mounting. When it bottoms is hammers it!
My current plan will give me 7 mm beyond the bump stops before the damper bottoms and 28 mm "drop" on the wheels. Do you think Guy, if I just used the existing lower mounting hole, which gives me 17mm (bump) and 5mm (wheel drop!) margin, that would be enough? In this case it's the limited wheel drop traded against an over-generous bump stop that concerms me! |
| Graeme Williams |
| Guy,
I'm not trying to score points just illustrate what's involved. The drawing only took about 1/4 hour while my tea was cooking and is only 2D which I'm fairly proficient at, don't ask me to do it in 3D as that would likely take me a week as it's not something I do that often. Regarding the upright dampers being stiffer I would say yes as as you say for the same valving more fluid is shifted so more energy converted to heat. Make me wonder with electric cars regenerative braking is often used to capture the energy from braking I wonder if anyone does regenerative dampers. An interesting demo of magnetic fields and induced currents interacting is to drop a magnet, especially a strong one neodymium type, down a copper tube. It takes far longer to come out the other end than you might expect as the moving magnet induces current in the tube which counters the magnet fall. |
| David Billington |
Guy: Thinking of chopping about a bit of 30x30x4 t section and fitting as per cardboard model (why do some pics come out upside down?). THe new hole position is 20mm higher than the old one and also forward, making the damper advantageously more vertical! I would hold the angle in place with the two u-bolt securing nuts currently covered by the "t section" |
| Graeme Williams |
| David, I was being light hearted, not serious! Some individuals do try and score points, but I know you are not one of thrm. It's very common on some forums, but the BBS has never really been prone to that.
Graeme, I don't know, but your 17mm excess bump stop sounds the better choice. You could always trim a little off the rubber of the bump stop to give slightly more travel and I think this would reduce - or make use of- part of that 17mm? Or, for that bottom plate how about welding a long bolt of suitable diameter along the forward edge of the plate, or along one surface. Probably more robust as a damper mount than a bolt through a hole in the plate. |
| GuyW |
| Gents,
I realize after consulting my notes that I posted some incorrect damper info' the damper I used is in fact a Kayaba EXCEL G part number 342002 NOT a Kayaba Gas-Adjust .I did buy Gas Adjust in the first place but the stroke was not correct as per the suppliers website, the Gas-Adjust is about 20mm less stroke at 368/243 so only 125mm stroke where as the Excel G has 145mm stroke, which is what I wanted. John, not all the Mini rear dampers have the same stroke and so they aren't all really suitable, I found that some of the information available online regarding open/closed lengths is incorrect ; important if the suspension is to work fully through its stroke.( I originally planned to use Mini Bilstein dampers but the stroke was actually less than the suppliers website said) The "sweet spot" that people are trying for is wrong IMO and will cause problems in the long term , mainly caused by inappropriate telescopic dampers supplied with some conversions, which will if set up so that they don't lock up before they hit the upper bump stop then they will allow minimal droop/rebound of the axle The Mini rear dampers feel good in use, softer than my old AVO Frontline dampers but still well damped , BUT I cant help thinking that the actual damper setting must be way off kilter for a live axle car as opposed to the mini suspension. Ian |
| Ian Webb 1973 GAN5 |
| Graeme I have some square tube with a wall thickness just short of 4mm from which you, or I, could make two suitable extensions to the original bracket which I can then weld on to make a neater and stronger job than your bolt on suggestion as per the picture. Alan |
| Alan Anstead |
| Ian: I believe the Frontline AVO dampers will work ok as long as you have lowered suspension. With travel of around 90mm a reasonable sweet spot can be found but without the spacers reducing the travel then they would be a bit more of a problem.
With a 6 or 7mm "overshoot" to allow for compressing the bumps stop, I can still have a 28/30mm allowance for the wheel to drop below it's normal position. Alan: we can talk about it on Sunday. I'm not sure how you could use box section. My scheme used steel, not paper although we do have some pretty good carboard which is quite hard to tear. |
| Graeme Williams |
| Graeme It is 63mm square section tube from which we can cut some L-sections to suit your purpose. I will explain on Sunday. Just going off thread a tad, but whilst you have the rear wheel off, can you measure the distance between bolt centres of your radius arms. I think they are 11" ? See you on Sunday. Alan  |
| Alan Anstead |
| Alan: Semi-elliptic....... ? |
| Graeme Williams |
| Too much on my mind. Alan |
| Alan Anstead |
| Alan: Ah thought it was a trick question! |
| Graeme Williams |
| Graeme, the bump stop compresses more than 7 mm when hit on a good bump, 12 is better. Ian, the way your car goes speaks for itself, doesn't appear to be a shortage of damping. |
| Paul Walbran |
| David's drawing very well shows the problem with angled shocks: as the axle is deflected towards the bump stop, the amount of damping reduces. Quite significantly in some set-ups. This is at its worst when touring two-up with a boot full of luggage. The car is heavier, so needing more damping, but sitting lower (and approaching the bump stop more often) so actually getting less damping. The result is quite noticeable. |
| Paul Walbran |
| Paul: 12mm is probably a safety margin I can't afford, not with these dampers anyway. I can make the damper more upright when I modify the mounting. BTW Paul, do you have any thoughts about how much the wheel would drop from it's rest position in the event of going over the top of a bump or on hard cornering? When you look at the way a semi spring is constructed and fitted you can't imagine it can drop very far, particualrly as the loads in play are quite low. |
| Graeme Williams |
| Graeme, a good start for working out the drop is the length of the rubber check straps |
| GuyW |
| Guy: No check straps because they were removed (by po) to fit dampers! One test I can do would be to jack the car under the front spring anger and see how far it lifts before the wheel starts to follow. As far as I can see, the only force on a wheel drop is the "dangling" weight of the wheel and any interia as the body lifts leaving the wheel weight to accelerate behind. |
| Graeme Williams |
| Plus the "push" of the spring itself as it is suddenly released from its compressed position at lift-off? |
| GuyW |
| Why not just get some shock absorbers with some more travel or a different length
They aren't expensive really Do it properly once and it's done None of these aftermarket kits mount them properly anyway To do it right the shock should never reach full travel in either compression or extended positions-They should stand as close as possible to straight upright from a side on view and at normal ride height the bottom mounting point and the top mounting point should be equal distances from the roll centre I think I used Mk3-4 cortina front shocks for the rear if I remember correctly but not 100% certain willy |
| William Revit |
| Just reset and remeasured and low and behold one or two critical dimensions have changed as the springs have settled and this is the other end of the axle too. The bump stop distance now measures 93. In reality , how are these supposed to work? The instructions say allow 10mm or more overshoot so tha makes the baump take up 103 and the full travel of the damper is...107mm!
If my axle wasn't lowered so much it would increase the bump stop distance and then what? Put it all back with the bracket with the mounting point underneath. THat will stop the bottoming out but 1mm free "drop" movement. Tried a short run seemed ok but no hump back bridges! Might put lever arms on! |
| Graeme Williams |
| Graeme. Rylan has some rear lever arm shocks for sale and is expected at tomorrows meet. If you want some lever arms, bell him tonight, and he can fetch them with him.. Alan |
| Alan Anstead |
| Graeme, in answer to your question about how far does it drop:
I haven't explored this on a Midget, but have on a B, where the situation is quite similar, and the answer was not as much as you'd think. The first set of Blisters I used on my own B had only 130mm stroke. By the time they allowed 12mm for bump stop compression that allowed only 45mm of drop from the rest position. Because the car was being set up for rallying, that was an acceptable compromise as I was looking for good bump control and less worried about rebound. |
| Paul Walbran |
| Haha, limitations on doing this on the phone, something hung. To continue:
On the unsealed rough stuff it worked brilliantly. However, on tarmac. Where cornering forces are higher, I was less confident and was concerned about sudden loss of lateral traction should the inside wheel lift while still providing useful cornering grip. As it turned out, in 20 years' hard use, including track work and tarmac stages, this never happened - the inside back wheel has always stayed on the ground. I would qualify that outcome by observing that suspension set-up has a big influence, and mine is soft rear/stiff front. |
| Paul Walbran |
| (by soft rear I mean the spring rate - standard - not the dampers, which are firm-ish.) |
| Paul Walbran |
| Sigh, I see auto-correct struck again. For blisters read Bilstein.... |
| Paul Walbran |
| Thanks Paul. On further googling I came across Daniel Stapleton's book and the section dealing with this topic. He specifically mentions the F/line setup but gives the impression that you set up the bump stop and let the rebound look after itself. Reading the F/line fitting instructions yet again it creates the same feeling. I currently have between -1 and 6mm rebound depending on which measurement I go by although putting it back today and having to lever up the suspension to get the bolt in, I would go by the -1mm!
|
| Graeme Williams |
| It's not much droop really-
As a guide you really need the shocker in the middle of it's travel, so "if" your shocky has 5" travel you would have it at 2.5" at normal ride height and adjust the bump stops to suit If it's a racer the aim is for 2.25-2.5" recorded travel after a race on the rear so really you would need to fit the shocker with 3" available compression stroke and 2" droop at normal ride height to allow for that and adjust the bumpstop to suit The mini shocks are only just long enough at 110mm stroke and will require carefull placement of the mounting brackets as you are finding out willy Anyone know the rear spring rate of a midget mgb springs are 90-135 but can't find the spec for midgets |
| William Revit |
| Willy, I have it noted down so where but can't find it. From memory, 85 +/- 2. Agree about ideally being in the middle of the damper range at rest, but given the choice of mud point or bump travel in rally set-up, the latter is even more important. And I found in practice the reduced droop wasn't noticeable on the road. |
| Paul Walbran |
| Found my notes. Mk 3 is 80 lb/in, mk2 75, mk1 98. I didn't record where I got them from, but I recall quite a search. Measured a new spring at 90. And the w/s manual gives working load 375 lb, free camber 4.45. As I recall camber is still 1/2 inch positive at rest, that works out very close to 90. Take your pick I guess... |
| Paul Walbran |
| Thanks Paul
Where I was going with that was to determine how far the suspension drops with a couple of pilots on board--so taking the springs to be 80-90 each, just roughly, with the crew on board at say 140 each the car is going to squat around 1-5/8" giving an extra 1-58"(40mm roughly) of available droop, so with Graeme's 1-6mm estimated droop empty, in real life with 2 up there should be roughly 41-46mm available droop which would be ok , -boarderline too short with one up at 21-26 but if it's just for road use it'll depend on the terrain and how angry the driver gets Bit of suck it and see really--I think it might be ok with the shocks in that position just--If it starts a habit of a new found wheelspin coming out of tight corners, you know what will be causing it, shocks running out of extension travel willy |
| William Revit |
| WillY: indebted for both your all all the other contributors' contribution to this rather lengthy thread. I have come to the conclusion that my best option is to leave it as I now have it - only the absolute minimun movement on droop but a reasonable safety margin on bump-stop. I think that is the best I'm going to get without changing the units. I may have a chat with Frontline about it and will report back. |
| Graeme Williams |
| Willy, that's a very good point which I constantly remind people about myself. The car can't be driven unladen so you always need to consider where it is withe the wright of at least the driver and some fuel, nominally half a tank. In light cars like the Midget, especially with the weight of the driver well biased towards the rear axle rather than in the centre as saloon cars are, the extra weight makes a big difference. |
| Paul Walbran |
| These keep appearing on eBay but I don't know where to get the conversion kit. https://www.ebay.co.uk/itm/123226089358 At this price (single) I don't think the conversion kit is supplied. I have emailed them and asked whether they sell the conversion kits. Still waiting for an answer. Rob |
| MG Moneypit |
| Rob, The heading does say "with conversion kit" No photo though. |
| GuyW |
| Willy, Paul,
If in order to determine the "bump" length needed for the shock, one measures the clearance between the lower eye fitting point (usually an adapted spring pan plate) and the car's bump stop, (allowing for compression of the rubber) then it makes no difference whether this is measured with the car laden or not. It still gives you the length required to avoid the shock absorber from bottoming out under full compression. You then subtract that figure from the design data for the full movement of the shock to find the length available for rebound. Clearly if the calculation is done with an unladen car it is already sitting higher on its suspension and less is needed for the rebound clearance if it goes airborn. |
| GuyW |
| Rob, It also says for 1 gas damper only (with conversion kit) so I guess the price is probably about right at ｣145 an axle set. |
| GuyW |
| It also says:- Dampers are for Models with Converted Rear Suspension Only Telescopic Damper So I guess the Gaz ones only fit if you already have a conversion kit fitted. Whether that be the vertical kit (frontline) or the inclined kit (Spax) it doesn稚 say. Simon |
| S Holt |
| Guy, no issue with that, quite correct in determining how to avoid bottoming out. What Willy and I were discussing was how to evaluate the amount of droop available once that mounting position had been found. This is the distance from at-rest to fully extended, and what we are saying is that the at-rest position should be ready-to-drive, not unladen, as the car will have at least driver and fuel when on the move. Unless the handbrake was left off... |
| Paul Walbran |
| Ah, I get you Paul. How does that relate to the amount of droop on a lever arm damped car, when this is limited by those rubber axle check straps? I recall complaints that they encourage wheel lift which I suppose to mean they are too short. On a standard car, driven hard, that is. |
| GuyW |
| Paul
when I was working out my current setup a couple of years ago I wanted to measure full droop so I did the measurements that i think you are refering to; with the car on axle stands I had 75mm between the rubber bump stop and the chassis bump platform ( the spring is more or less flat in this static condition), I then jacked up the chassis with 8.5" check straps fitted (no dampers of any type fitted) then when re measured I had 135mm so therefore 60mm of droop . I also measured without the the check straps fitted and it was only 6/7 mm more. My damper selection was based on this 135mm plus +13mm for bump stop compression, so 148 mm . The KYB damper I used has 146mm of stroke , not quite enough ideally when including 13mm of bumpstop compression but I decided to risk only 11mm of rubber compression. I have thought to fit some 1/2 shorter check straps to make it well within the damper operating stroke. Ideally a damper of 150mm/6" of stroke would be perfect but I cant find one that id short enough when fully closed , and will fit into the standard chassis. It would be necessary to fit a small turret for the top mount for a 16"/10" damper....which we discussed before. Ian |
| Ian Webb 1973 GAN5 |
| Got into the shocker catalogue today, just to see if there was something there that would fit straight in----------bingo
2011-2013 Hyundai Elantra rear shock Same ring/sleeve fitting on both ends- Unsure of the bolt dia and sleeve length but that sort of thing is easily worked around c/c lengths 248-389 So by your measurements with the bottom plate inverted of- 17mm into the top bump stop and 5mm droop with your 107mm stroke 245/352 shocky If the Hyundai shocker was fitted with the brackets in this position the result would give 10mm into the bump stop at full compression and with the longer 141mm stroke and different starting point 46mm droop which is within a couple of mm of the droop you had with the bottom brackets the other way up Best of both worlds really Might be worth a look at if you were thinking of new shockers This was in the Monroe direct replacement cat.-other brands could vary I guess The only other one that went close was an early VW beetle 251/391 but slightly too long compressed (but still 7mm past the bump stop)BUT plenty of Formula Vs racing so having a chat to someone with one of those might be worthwhile as they sit a bit closer to the ground than your average beetle and would possibly run shorter shocks-- there would be plenty of aftermarket racey shocks laying around amongst those guys to choose from willy |
| William Revit |
| I got a reply from that ebay seller. They no longer sell the conversion kits. Pity, they would sell a hell of a lot more if they still did the conversion kits. They didn't say if it was the the SPAX type brackets or not. A while ago Charlie Chapparell (if that is the correct spelling) suggested EMPI for VW Beetle rear ends. I can't remember the part number though. I think it was a coil over shock without the coil. Rob |
| MG Moneypit |
| The GAZ units are 15" with 5" stroke- 127mm c/f 107mm on F/line. Would need fitting keit because they would not fit using the check-strap mounting. Apaprenlty Midlans Sports and Classics do the complete set up |
| Graeme Williams |
| Midland sports don't list a kit for Sprites (but for B's and C's) and neither do Rimmer, the other suggested reseller. What a minefield for mis-sold parts! |
| Graeme Williams |
| (Sorry about the patchy posting)
It stands to reason (lol!) that the mechanical interiors are not going to be vastly different betwwen one telescopic or another. Ok, maybe one maker will squeeze an extra 5mm compared to another but essentially telescopics of the same length are going to have very closely the same stroke! The Gaz are 15" with 5" stroke; the AVO are 14" with 4" stroke and I bet Maker X's 14" are also 4" The answer seems to be somehow fit 15" or greater and put it on the tilt to effectively increase that stroke. Which is why mose use the original mounting points and not the check strap hole! |
| Graeme Williams |
| Graeme, I don't think that is strictly true.
When I first fitted shocks to my car I just bought some mini front ones off e-bay. I don't remember the brand. After about 15 years of use the shrouds began rusting and looked pretty scruffy so I bought another cheap mini set, only to find that they bottomed out. I then bought some Monroe branded ones, still fairly cheap as I recall and they had a longer overall stroke but still fitted directly to the car with no further modification.(i.e between rubber drop strap top mounting and inverted bottom spring plate) So there are construction variations between brands. |
| GuyW |
| Guy, I have been assuming the std droop, limited by the check straps, is the baseline for all this. Rear wheel lift usually doesn't occur unless the rear springs are harder than normal. There is a wonderful period road test comparison between Spitfire and Midget showing great photos of both cars at their limits! And the Spitfire showing what wheel lift really is. :-) |
| Paul Walbran |
| Ian, good info on your setup thanks. Willy, we had the VW shocks on at one stage, dims right but rate too harsh. The suspension shop guys said that have different bump/rebound characteristics due to using torsion bars. I gave up trying to get that, but they were horrible to ride and made the car twitchy on the track. We are now using Bilstein 46-0296, has 140+ mm stroke iirc, and a reassuring rate. Car now feels much better balance with good ride. |
| Paul Walbran |
| Just searched Google images for Triumph Spitfire wheel tuck: www.google.com/search?client=firefox-b-d&channel=trow&biw=1920&bih=938&tbm=isch&sa=1&ei=DQsSXZH5ENGua63BvfAE&q=triumph+spitfire+wheel+tuck&oq=triumph+spitfire+wheel+tuck&gs_l=img.3...265109.265865..267101...0.0..0.170.357.2j2......0....1..gws-wiz-img.......0i24.5vGiGt0yZO8 Enjoy ;-) |
| Jonathan Severn |
| All good Paul-thanks for the info I wonder how the Elantra shocks would go, the measurements are good ,but-? I really like Blisters - lol I used to run them all round my midget,the fronts were mounted inboard operated with rockers and a 5th whopper big one from the floor up to the top of the diff housing to control axle tramp ,it worked a treat without binding eveything up |
| William Revit |
| I have spoken to four companies this morning.
I can rule out Bilstein (sorry Paul) as a) not terribly helpful and b) "no we don't do one for Sprites, only Minis" Spax use a 15" to achieve 124mm movement and mount off a special braket mounted on the original lever arm mounting holes. Gaz use a 15"/127mm shocker The F/line is 14". Their suggestion is to set it up to avoid bottoming out and were rather vague about the other end of the movement range. My conclusion therefore is that mounting a damper in the check strap hole is always going to be a compromise if a 14" damper is used. You can avoid bottoming out or topping out but not both. That can only be achived with at least a 15" unit which could be fitted Frontline style and with a small adjustment of the lower mounting hole could give a 40mm wheel drop. Still not a lot! Don't know whether there is a 16"! That would be even better. Perhaps lever arm has a lot going for it! |
| Graeme Williams |
| >> . . . and were rather vague<< - I very much doubt it, must be your lack of comprehension, you not a being an expert like they are. "All Frontline's new upgrade packages have been conceived, developed and rigorously tested by Tim." You must have an old development, buy a new one from them and all your problems are over. https://www.frontlinedevelopments.com/about/meet-team/ |
| Nigel Atkins |
| "Perhaps lever arm has a lot going for it" Personally, I prefer lever arms to angling the shocks due to the drop off in damping from the latter when the car is loaded and further down on its suspension - right when you need it. For that reason I reverted one of our cars from Spax to lever arms and found the result to be much better overall.
I should have added that to fit the Bilsteins we made a new extended bottom bracket with the attachment point 40mm lower than the upside-down standard bracket. Doing so is a relatively simple way of increasing the range of options for fitting vertically mounted shocks. |
| Paul Walbran |
| When I close my eyes at night I see dampers rather in the way that Microsoft used the "flying toasters"! |
| Graeme Williams |
| Paul,
I agree about lever arms and have experienced decent ones on my Austin A40 Farina, while they failed the bounce test initially, refilling with EP90 made them sweet and normal and they were mechanically tight and worked well unlike all the ones I had on my Sprite where the recons were no better than the ones they replaced. That lead me to designing the front damper replacement upper arm and telescopic arrangement, the rear of my frogeye has upright telescopics and the difference between them and worn LA dampers is very noticeable as I'm sure your aware. I considered rebuilding my LA dampers but thin wall bushes were not available and I didn't have the kit to make them at the time unlike Peter Caldwell. Rebuilding the A40 steering box revealed that Vandervell had at one point made 1/32" steel back bronze bushes which is what I removed from the steering box, if I could have gotten some I might have tried to rebuild some LA dampers with them. |
| David Billington |
| All this jumping between imperial and metric is doing my head in---can't we just do one Graeme Mounting in the checkstrap hole isn't a compromise, you just need the right shocker Did you check out the 2012 hyundai elantra rear shocker 248-389 ---(15.3" x 5.5" stroke) I suspect a Kia Rio same year would be the same -? I cross ref'd Pauls Bilstein No and it's from a 2 series Volvo rear |
| William Revit |
| Willy: I gave the number to Bilstein when I spoke to them yesterday and they said there weren't enough digits! but they couldn't really be bothered to check anything out.
I hadn't checked out the elantra simply because I wondered how the stiffness and bounce specs would suit the car. I'll have a look on a couple of damper manufacturers' sites. I can't see any reason why I can't put a 16" (407mm) unit in the same position as the current ones. I wonder why F/line don't do that? Perhpas it would foul on something i haven't noticed? |
| Graeme Williams |
| 16" could be ok but you would be pushing it to get a suitable compressed length unless you are prepared to manufacture some new or modified bottom brackets---it mainly depends on the stroke I'm thinking you need around that 5"-5.5"-X -15.3"-----which the Hyundai unit has Paul's part no only needed a "B" in front of it-------B46-0296 The Bilstein dude should have known that |
| William Revit |
| On a 1500 the checkstrap hole is considerably strengthened with the additional chassis member.
On a pre-1500 it's different and doesn't look strong enough especially if the shocker bottoms out in compression due to lack of stroke. Also, pre-1500s have a lower ride height. What strengthening is recommended in this area for pre-1500s? Also, why did SPAX develop the conversion bracket that put the shock at an angle? Why didn't they make the conversion plate a bit bigger to make the shocker more (or fully) vertical? Rob |
| MG Moneypit |
| Blimey, bit of brain fade there, thanks for correcting the part no Willy. Also Bilstein have superseded their numbers since I first selected that, another barrier for a lazy sales type. Rob, Spax (and others) angle mounted due to not having a unit with sufficient stroke for the room available. To be fair, short overall length and long stroke is a challenging design issue, doesn't leave much room to fit the valving etc. |
| Paul Walbran |
| Avo tell me the F/line units are specials. Reluctant to say much but apparently the offset top fitting is not standard.
Did 60 miles two-up with no clonks. No obvious issues with topping out either. The ride is still quite choppy (no reason why that should have changed one way or the other), which was just my experience with an MGA with telescopics. Apart from the lowered ride height the only difference between this and my frog are the teles v lever arms. THe Frog rides and handles well which makes me wonder why telescopics are fitted here. Bought two lever arms in need of restoring for ｣15. I'll cost out the couple of other bits I need and decide. |
| Graeme Williams |
| Here is the offset top mount on the AVO "special" rear damper. Ian  |
| Ian Webb 1973 GAN5 |
| I tried a telescopic conversion on my road Frog as few years ago and there was no difference in the handling as far as I could tell. Went back to lever arms. My modsport frog had turreted adjustable vertical telescopics which were superior to the levers but then it was a somewhat different vehicle! |
| Bob Beaumont |
| Bob, I think you must have a rare thing, a decent pair of LA dampers. I found the difference immediately apparent when I fitted telescopics to the rear of my frogeye as it removed the obvious float due to wear in the LA dampers allowing some undamped motion in the suspension. |
| David Billington |
| The dampers were the original ones (dated stamped 1960)! I replaced the damper oil, gave them a clean up and all was well. Fortunately the arms moved without any float. The fronts were not so good with lots of undamped movement and were replaced by a pair of NOS ones I discovered at an autojumble. Vast difference! |
| Bob Beaumont |
| I find the ride with telescopics very "choppy". Have been running a bit on the soft side so have wound them up today and will try tomorrow. On the MGA the telescopics would remove fillings irrespective of setting. |
| Graeme Williams |
| The first set of tele. shocks i had in my midget were adjustable for bump only and the rebound was very stiff, problem with them was the midget springs were'nt strong enough to push the rebound back and as you drove along the bump would push the shockie in but because the rebound was so stiff it didn't have time to reextend before the next compression and gradually the rear of the car got sucked down and became very stiff and skippy---Took a while to pick up on it being a trailered racer until after one session I got back to the pits and jumped out and thought it must have broken a spring ,it was sitting so low. --went off to get the jack to lift it up to have a peep at it and when I got back it had returned to normal height
Just too stiff on the rebound---Got myself a nice set of gas Bilsteins to match the springs and made up some mounts for them and it transformed into a good handling grippy little jigger |
| William Revit |
This thread was discussed between 17/06/2019 and 28/06/2019
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