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MG MGB GT V8 Factory Originals Technical - Antitramp, different easier approach possibly
|Although fitting antitramp bars is not particularly difficult I was thinking about how they function. You've got a solid bar running from below the spring eye and attaching below the middle of the spring at the axle. So how is this different from just clamping a length of steel to the front half of the spring?. The answer could be that although there can not be forward and backward movement in the spring above the bar, there is just a little curve flexing going on.|
This seems to indicate to me that if you were to attach a length of steel above the spring from the axle to directly behind the eye of the spring this would allow the spring to flex as per the usual antitramp bars but woudl prevent any forward movement. Also this would very definitly prevent the spring from ever reversing.
Also, rather happily, there is already a projection on the axle in just the right place to attach a link, it even has a hole drilled in it!. This is the U bolt locator (you know that bit on the underside of the axle that has the rubber bounce strap bolt on the back and that unused projection on the front). I envisiage bolting a length of channel steel (walls downward, directly to this projection and clamping the front of the lenth of steel directly behind the spring eye. The steel should locate tightly behind the eye and a bolt under the spring between the walls of the channel steel would hold it firmly to the spring. This would allow the spring to move but prevent the axle pushing forward and flexing the spring under power. Could even bolt up to the spring eye bolt if wanted, although without the isulating bush more vibration might be transmitted. The advantage of doing is is that it is very, very easy to do ie cut a lengt of steel, drill a hole in one end and a hole in the other, done!
Also this does not hang below the spring and cause any ground clearance issues.
What do people think? am I on to something here?
What are the problems , if any?
|You'll get some interesting bump behavior and I'd be worried about the point load on the spring over time. Thoretically you'll be triangulating the axle so it "could" work but I'd not want to be the first to try ;?)|
|Peter, a semi-eliptical spring effectly changes length as it bends, hence the need for a shackle on one end to accomodate this change. An anti-tramp bar should be the same length as the front half of the spring measured from the spring eye to the center of the axle. It should also be mounted parallel to the spring and have rubber or urethane bushings to allow for this length change for a street driven car. If the bar is not parallel and doesn't have some sort of compliant bushing the pinion angle is changed as the spring moves through its arc. It also imparts a twisting force on the axle housing as one side is compressed and the other is not. |
This compliance does theoretically allow for some axle tramp, but in practice on most street driven cars it doesn't seem to make any difference and the improvement in ride more than offsets this factor. Your design would indeed prevent axle tramp, but I think the ride would be very harsh, effectively removing any spring action from the front half of the spring.
Valid point about point load however bearing what you say in mind the front of the bar could be shaped a little to locate tightly up against the spring eye and the other end is attached to the axle, so there should be no point load on the spring. Possibly even wedge a bit of rubber in there. There is a triangulation kit that the MG owners association sell for around 100 pounds except that one clamps from spring to a point about one foot inboard on the axle and apparently causes the roll center to move up. I'm not attempting to triangulate but to simply keep a straight line so there should be no roll center issues.
You'd need bushing if the thing was moving about an independent axis (like traditional antitramp bars) but this is not. There are no axes of rotation 'cause the front is fixed behind the eye of the spring and the rear is fixed to the axle. Your very valid question about the curve in the spring changing the straight-line length is also applicable to traditional antitramp bars. There is a possibility that the off-set to the traditional antitramp bars compensates for the spring movement, that the front eye of the bar is off set a little (i.e. on the top of the bar) then as the bar swings downward it moves forward a little, but I do not see any evidence of that. I suspect that there is negligible spring length change at the front of the spring, which is how come the traditional antitramp bars work. Anyhow what I'll do is tie/fix a trolley jack to the rear spring and compress and release it over the length of suspension travel to see if there is any significant change in straight line distance compared to the location points of the traditional bars.
|Well, that didn't work at all!. The "top of the spring" locations moved about 5mm closer as the axle travelled through it's arc. The usual style of antitramp locations below the spring stayed exactly the same distance apart throughout suspension travel. It took a while but I realize now why this is so. If you think of the axle end of the tramp bar location as being at right angles to the surface of the spring and roughly 5cm below, then as the spring goes from flat to more curved this point rotates toward the back end of the car, just a little, infact this rotated distance is (or rather can be if carefully set up I hope) the same distance as the distance the axle moves closer to the eye of the spring because of the spring going from flat to curved.|
So I'm off to make some standard type antitramp bars.
Can anyone who's done this tell me what size tubeing they used for the bars?, what wall thickness and diameter?. I don't want to go too heavy with the unsprung weight issue. Also crucially what distance below the spring eye and shocker mounting plate (below the axle) did they mount the bar? Are rose joints necessary at one end of the bar because of axle movement twist, or is there enough flexibility not to notice a need?
|I use 25mm diameter aircraft tube (25CD4S), 3/8” rose joint and polyurethane bush for triumph|
I do not have problems, the system work very well.
|Michel, beautifully engineered bars. I used 1" thick wall steel tube for the bar and found tube which would house stock rear spring eye bushings which I welded on either end. No problems if the initial measurements are precise. Adjustment is nice, but not absolutely necessary.|
|I'm just finishing up mine, 1" OD, .06" wall thickness. I ran the buckling equations for the length, they will take lots of rear end torque and not fail. I welded junk MGB front A arm bushing mounts and turned a threaded insert for a heim joint on the other end. Pics at http://www.et.byu.edu/~jmv/rear_suspension.htm|
|Thanks gentlemen, 1 by 0.06 it is.|
Immaculate undercarrage , Michel, I wish mine looked as good (I can't access your pictures Jake). I do like the idea of using front bushes as I could just go and buy a set off the shelf however I think I will check out the price on rose joints first although I get the impression that they might not be necessary (just very nice to look at, which is not such a bad thing) I need to think about it awhile. I can always add them later if they realy prove necessary. Any signs of stress due to their absence Bill?.
Interested to note the reinforcement around the spring hanger Michel. My car is an EX-rubber bumper and I've lowered it by blocks and redrilling the front spring hanger. This leaves a hole below the spring eye that very frustratingly is just not quite far enough down to fit the tramp bars on, so I must add in an extension. How far along the body of the car does your bracket go Michel?, or anyone else if they've done this. I had considered that the reinforcing around the rubber bumper hanger sufficent and that I would just bolt on a couple of triangular plates either side . However I notice that there is some signs of strain around them already. No bent or torn metal or anything like that but the rustproofing bitumen around them has cracks in it indicating some stress/small movement going on there. That stess is not going to get any less If I add tramp bars I figure.
The alternative is to brace all the way to the jacking point cross member. I saw some metal shelving material in a hardware store that seemed about right for the job. I would have to rivet it up as my welding skills are not up to overhead work with an arc welder, Alot of work all the same!
|Check out http://www.theautoist.com/RearSuspension.htm#Top%20Hats:|
(Tony Barnhill's site) This might give you some ideas.
yeah, sometimes the server at school is down, you just have to check back later.
|Jake, piece at a time it bids to out do Michel eventually. The rose joints do look good. That bounce strap point does look a good place to weld on a pan hard mount/bracket, or I might possibly even bolt something to the aluminium block below it(I've got blocks as well) Can a panhard rod be too low I wonder?|
Wayne, that welding look about the same standard as mine! However I think it would not be easy welding over head. I think I'll stick to allot of largish rivets, if it's good enough for aeroplanes it's good enough for me.
|The car is for track day use with much modifications. The new bracket for the antitramps is welded to the origin leaf spring bracket. On the MGRV8 the bracket is much more long to the front of car. Sorry for the shot quality, it is a scan. I have fitted also a Panhard rod.|
|Some very nice welding Michel, you must have a mig or Tig (plus some talent) I think. Photo exactly what I wanted to see. I might just try it with the simple triangular plate aproach first because (A)it seems to work for you and (B)the rubber bumper car is already reinforced around that area and the plates will make it stronger and (C) I'll keep a close eye on it at first then if necesssary add on some bracing. (and (D) I'm lazy!)|
Very interested to see the orrigional chrome bumper rubber bump stop location(confusing sentance!), in the rubber bumper cars there is a section welded in that virtualy comes down to the bottom of where your stop is and the pededstal on the axle is far shorter. You can really see how that area was orrigionaly designed to take a a coil spring. That reminds me Jake, if you find that you've suddenly aquired a lot of oversteer after you finish lowering the car simply cut about 20mm off the bottom of the rubber stop. I came across this simple easy cure quite recently. Used to be that about half way through a turn some, sometimes alarming in the wet, sudden oversteer would mannifest. Achording to various sources this bumpectamy gives the ideal suspension travel of between 2 and 2.5 inches (2.25") as opposed to the 1.5" you'll get otherwise. There's no danger of the shocker links contacting the bottom of the car but I silicon glued a bit of rubber up into the centre rubber bump stop hole afterwards anyway just to firm them up. (Used recycled bump stop)
Michel is that orrigional chrome bumper bump stop pedestal on the axle? It looks ideal for the makings of a very easy solution for a light weight bolt on point for the pan hard rod (rotated through 90 deg).
|I've been thinking about this some more and it occurs to me that with a pair of tramp bars and a panhard rod I'm three fifths of the way to a five link set up. All that needs be done is to put a pair of coil springs in the place they were designed for (bump stops). The question is what do you use for the upper links without embarking on a major undercar reconstruction.|
Then it struck me that I could possibly use the rear shock absorbers as the upper links. They are very strong and are already in the right place.
As you know the horizontal rear shock absorber arms are located 4 or five inches above the axle and point backwards. I could easily make a short extension that could U-bolt to the axle. A piece of shaped angle iron with a bush on the end to bolt to the shocker.
Obviously the bottom "tramp bar"/link is about four times longer than the shocker arm and moving through a much more shallow arc than the shocker arm. This implies that at the top and bottom of the suspension travel the axle will rotate forward just a little; however since the suspension travel is at the most 2.5 inches total this could only be one or two degrees at the out side. Especially when you concider that the shocker arms will be attaching to "towers" that locate roughly 5 inches above the axle. I will have to work this out and check exactly, it should be easy enough to calculate. The point is that currently with leaf springs I must be getting far more movement that a couple of degrees. Just general suspension movement and more extremely axle tramping.
The big advantage is that I can throw away all that unsprung weight of the leaf springs. The short shocker arm "tower" should weigh about the same as the shocker links and (in my case) spacer block and bottom U bolt gear. I would imagine makeing a clamp on arrangement that locates the bottom link under the axle (where the tramp bar goes and on the top of the axle the short tower (displaced a little to the centre)
I under stand Coil springs are also more responsive than leaf and I also kind of like using the shocker arms as a link, just like at the front. Consistent.
What do people think about this?
Does anyone who has put in a five link coil sprung suspension system have any information on the springs they used, height, strength/heaviness/ compressibility etc. This is figure will be my major expence, and hopefully not too major.
|Peter, remember that the suspension does not move equally on both sides. If you impart a rotation to the axle housing from movement on one side and the other side is stationary something will break. The axle housing will not twist! That's the reason suspension components for live axle cars must be set up so that the locating arms are equal length and parallel. |
Major changes to the suspension will require a lot of reinforcement of the chassis where the new components attach. As you stated in a previous post, you don't weld, so I'd advise sticking with a simple set of anti-tramp bars. Remember that a suspension failure could well put you off the road at speed, so make all modifications with high quality welding and with a safety margin in the materials selected. Light weight stuff is for race cars, not the street.
|What year is your car? I have been thinking on this issue of a 5 link as well, what about using the rear anti roll bar chassis mounts to hold the upper bar? Making another set of tramp bars, same length and all, should be sufficient for the upper links. You would just need a way to tie them into the axle housing on top. |
When I determined if my tramp bars would buckle, I purposefully neglected any stiffness from the leaf spring with that idea that some day, the leaf springs would be gone. Its still a little ways down the road, but should work when its ready.
| Bill is quite right, torsion forces could be sorted out by a couple of rose joints but because the two towers (LOTR!) make a kind of H then there would be an arc transcribed, i.e. no way.|
Jake, my car is a '75 and just missed out on the rear antisway bar. In this site I've seen a variant where there were upper bars using the antisway position. However since the heel board slops backwards the upper bars were still a little shorter than the bottom which would certainly work but not be ideal as says. I also suspect that the antisway locations are too high, like the shocker arms.
I'm now thinking that since the upper and lower links need only be a little more than an axle width apart (one on the top and one on the bottom)it might not be too hard to make a bolt on double mount at the spring hanger. Ignore the spring mounting point as a link mounting point and use it to attach a plate with both the upper and lower link mounting points on it, one above the other so they could be the same length. This could be a piece of channel steel (or two pieces of angle)more or less right angle shape, attach at the top of the heel board (much as the antisway bar location (If I had one!) Goes down, turns right angle around the hanger and then along the floor to the center jacking point cross brace It would be very strong and easy to construct and of course bolting on primarily at the spring hanger (the strongest spot), and at either end. With some fastenings onto the floor. Can't see any problems with that. Of course if I changed my mine (for whatever reason) this arrangment would not interfere with refitting leaf springs and would certainly be useful for tramps bars etc. Would use a set of front bushes on the bars. maybe get them professionaly mig or tig welded after I tack them up.
For suspension, discard the hydraulics and bolt on some adjustable coil over shocks much as the SPAX set up, which would sort out the ride height exactly.
|Just found an article in a magazine "MG enthusiast" vol 35#2 April /May.|
This is a bolting 5 link suspension.
The new take on this is that they cleverly linked the spring hanger with the shocker mounting point so that the suspension is pushing through the frame and would be tremendously ridgid and strong.
I'm sure even I could make up a simplified version of this. Not so pretty, but well out of sight.
This is their web site as quoted in the Mag'. There is likely to be something on it (havent looked yet)
|Just checked, nothing there, looks like you'll have to buy the magazine.|
|I did post some pictures of my set up on Mike Barnes,s site:|
I just tried the link but it doesn't go anywhere. Is there a mistake in it or is my ISP.?
|try this http://www.mgcars.org.uk/v8_conversions/|
|The link i had to the frontline costello front and rear suspension no longer works, however I have an Adobe file 333kb. that I could e-mail to any one that wants it, contains pictures and fitting instructions.|
Will provide you with a number of photographs of the Frontline Costello suspension on my "factory" B GT V8.
The folder also includes copies of a couple of Frontline Costello's documents, including fitting instructions.
I am delighted with the modifications.
|Sorry the link is correct but for some reason it doesn't connect.|
Please try cutting:-
and pasting it into your browser.
Anyone know why the direct link fails please?
it's such a long time since I dropped in on here that I cant even remember the link....
All the interesting details that I wanted to see that the magazine article didn't show. I somethimes think the people who write these things aren't quite switched on. Lots of pointless pictures of cars zooming dramatically about the place with various personages at the wheel but not much nitty gritty.
I won't be home for a few weeks yet and can't get under the car to have a look, but it occurs to me that a simplified version could be very easily made up. I don't see why the top bar needs an offset, that the elaboratly shaped link could not be a simple piece of steel. Have to go look.
Any way it's damn clever linking the spring hanger with the shocker bolt on spot. the suspension is feeding force evenly into the entire car, no weak spots. Infact if you set the links up with a little downward bias they would push the back end down under acelleration and increase grip/traction hence accelleration. Not only that there is no longer a leaf spring bouncing up and down next to the fuel tank and that and opens up new possibilities with respect to fuel supply, lots of room around the fuel tank.
This thread was discussed between 02/06/2005 and 28/06/2005
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