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MG Midget and Sprite Technical - spax replacements

I'm replacing the rear spax shox on my midget at some point and was wondering if anyone had recommendations for alternative units? I'm looking for straight replacements so please don't suggest the frontline kit ;-)

Graeme
graeme jackson

What, No frontline kit for you? HUH, next you'll tell us your yearly bonus from work is less then 5 million pounds...LOL

Here is a great site about a rear tube shock conversion that I understand to be vary good and seriously in line with the common mans wallet

Just a note Id try and keep the brackets, those are hard to find and I think add to the strenght of this type of mod job.

any chance you can make a paper copy with good specs and sizes for here on the BBS or at least for email, id certianly love to make a pair of the brakets for when I do my lever to tube conversion

http://82.44.126.36:76/shocks.htm

Prop
Prop

A temporary installation which has worked so well it's now become permanent. G-Max mini fronts off fleebay for a couple of shillings - washers and bolts were pennys.

Andrew Dunn

Well,,, thats one way to build a spacer LOL, please tell me the hardware is at the vary leaste grade 5.

even grade 8 is scary with 30 flat washers


Prop

Prop

hI, I followed the instructions on the site suggested by prop and it massivly improved the ride. i used a pair of standard mini front shocks. i was advised not to use uprated shocks on the rear cos the ride will be too harsh.the rest of the bits i already had in the garage, i also turned the bottom leaf of the springs upside downand put it on top, it dropped the rear about half an inch sits much better now and cheaper than a lowering kit, good luck.
p sewell

We currently have AVOs from Frontline on the racer (albeit these are not compatible with your SPAX).

I am in the process of replacing them with a set of Pro-Techs which is what I use on my Ginetta G15 Racer (and which are factory fit for the Ginetta G50 racer).

http://www.protechshocks.co.uk/

I'd give them a call on 01225 705553 and discuss it with them - if you can send them on of your old SPAX units they can copy the damper open and closed lengths, as well as the 'eye' sizes, and also set the damper up to what ever rate range you require.

Last time I bought a set (about October last year for my mgtf) they worked out about 70 GBP each (so cheaper than SPAX).
Deborah Evans

"Well, that's one way to build a spacer LOL, please tell me the hardware is at the very least grade 5.

Even grade 8 is scary with 30 flat washers"



ESPECIALLY given that the mounting bolt is in single shear!

Failure waiting to happen I'm afraid.
Deborah Evans

Looks like a mod from the Dangerous Brothers, good job you don't live where i do, you'd never make it to the end of the lane!
Brad (Sprite IV 1380)

Going back to my original point that I want to replace the spax exactly, i.e. using the brackets that are bolted where the old lever arms were, can anyone tell me if the GMAX mini fronts are a direct replacement? Unfortunately I can't measure the old shox as they were totally shot when I stripped the shell and went out with the rest of the rubbish.

Graeme
graeme jackson

even if (i don't know) they are the correct lenght i would never use mini Gmax shocks on the rear of a midget
they are way to hard
for a good handeling car you want a rather soft rear end and Gmax's will not give you that.
if you go mini go adjustable or std
Onno Könemann

cheap mini standard shockers

mine cost about £14

they fit inside the upper rebound strap location and drop down directly to the spring mounting bracket which you have to take off the one side, switch to the other side and turn upside down. So you have nearside platform upside down on the off side and vice versa

The problem you have then is that the upper strap location isnt designed or stressed to take the effort involved and needs reinforcing I did this by welding a large washer to the outer faces of the mounting bracket and welding a reinforcing brace to the inner section

After the upper brace section STARTED FALLING OFF THE BODY I had to spend lots of time upside down, "working in the dark dahn below!"

The picture shows the results of unstrengthened fitting

That handy U section is only spot welded in place because it wasn't designed for any other, harder task

The shocks are my cheapo Mini ones

bill sdgpm

The wear and tear shown after tapping the section back up into the arch, before welding the brace...



thinks.. plan A isn't always the best way :(


scary stuff

bill sdgpm

OK. Do the standard mini front shockers fit in place of the spax shockers USING THE SPAX BRACKETS?

graeme

graeme jackson

Well nothing is going to be a direct exact replacement to the sprax.

And I doulbt no one here can tell you with 100% certinty that the mini front shocks will bolt on the the sprax hardware and brackets trouble free...Its rare that someone will convert from $500 shocks to $40 shocks

But for $14 GBP, Id order one and see what happens, if it dosnt you can re-sell it on evil bay and try agian

My personal opinion is yeah I think it will fit, it might take some love and hate mod work, but I think it will fit.

Its 14 gbp. try it and see... and let us know


DEB...
If your just upgrading Heck maybe our friend might like to purchase your used AVOs with a pair of matching brackets after all I think those are a 10 point adjustment
Prop

Graeme
To try and answer your question directly. I have the angled Spax brackets on my car and have been using AVO shocks bought directly from AVO. The part no. listed on their website is TE548, but it's worth a phone call to check. (I tried looking for my invoice to verify but couldn't find it!). They are £70 each though!
Regards
Keith
Keith Nelson

"ESPECIALLY given that the mounting bolt is in single shear!

Failure waiting to happen I'm afraid."

Throwing the numbers at it says it won't fail in either bending or shear. Even if it does it won't be catastrophic - I'll just loose the damping effect and have a lump of shocker banging against the axle casing for a few yards. I'm cadding up a permanent fix but until I can get the welder fired up I'm sure it will last.
Andrew Dunn

if the axle is on the body you can meassure
just jack it up until the axle hangs in the straps and meassure from mounting point to point.
the put it on it's wheels and load up with lots of weight so it hits the bump stop and meassure again.

now you have the max and minimal size if the mini shock fits in these specs than you're okay

please pay attention that the minimum of the shock can not be bigger than the minimum of the suspention
and that the max is not smaller than the max of the suspention
Onno Könemann

Graeme,
You didn't mention what year you have - they are different for pre 64, 64-74 and rubber bumpers.

I posted the dims for a '64-74' set and from the archieves thread G736/180 14-02-07. search under 'spax rears'.

Spax shock units G736 CZ2

260mm centres closed
380mm centres extended.

HTH.

R.
richard boobier

>>>>>>>Throwing the numbers at it says it won't fail in either bending or shear. Even if it does it won't be catastrophic<<<<<<<<

catastrophic??? As in the planet crashing on its axis and catching fire killing all life forms on earth? No of coarse Not! Will all still be here to go WOW did you see that, Un-Beliveable!.... I knew ol andrew, he was a great guy, Im gonna miss him. LOL.


Prop
Prop

A few thoughts on the above:

Bill's observation on the upper mounting:

"The picture shows the results of unstrengthened fitting

That handy U section is only spot welded in place because it wasn't designed for any other, harder task"

Agree - but observe that said spot welds weren't even up to the original task as I have seen that sort of failure even on cars which have only ever had the check strap there (though to be fair they are likely to have been driven vigourously over some of our gravel rural roads and may have left the ground occasionally!)

Onno gives good advice about the desirability of matching shock travel to suspension travel.

The Midget has a bit over 6" on the rear, IIRC the Mini shocks are somewhat less. They will probably be fine (certainly going by Bill's experience) until you hit some very lumpy stuff, then it will run out at one end or the other or both, depending on set-up. Main problem will be if it bottoms out before contacting the bump stops, which will stress that upper mounting and ultimately shorten the life of the shock unless it has a built-in bump stop. You could overcome this by packing the bump stop or its landing plate so they contact about 10mm before the shock bottoms out.

At the rebound end, losing an inch of suspension travel is unlikely to be too dramatic unless hitting a bump while cornering hard. Theoretically if the inside wheel lifts off the road suddenly while still making a significant contribution to lateral traction you might find the tail wags. In practice this was never an issue with the first set of Bilsteins I tried on my MGB until I found one with more travel.



Andrew is completely right about the loadings.

Increasing the length of the mounting bolt as he has done will not change the shear, as SHEAR on a canilever depends only of the load and the cantilever section and is independent of the load position.

It will increase BENDING moment substantially. However, this is mitigated to a large extent by the un-pretty but wrongly maligned flat washers. Done up tightly, they will act strongly in compression to resist bending of the assembly but have no contribution at all on the tension side, which is handled by the bolt - which must be strong enough to do the job, so the comments about bolt grade are correct in this sense. This will be the same whether it is 30 washers or one large spacer.

It is hard to say for sure without seeing the whole thing, but the washers are of sufficient diameter to make the assembly (of bolt+washers+mounting) perhaps more rigid than the plate they are attached to, since it is only about 1/4" thick and narrows as it forms the mounting eye. Ultimately fatigue from flexing could be an issue. If you have to have the shock that far displaced from the mounting plate a stiffening gusset might be worth thinking about in the permanent version.

My hunch is that the top mount would be the first to fail unless it is reinforced, the fatigue from flexing would probably be greater around those few spot welds than in even the extended lower mount.



Paul Walbran

one day I might build a proper strong upper mount and remove the flimsy one but to be honest I would want the car turned on its side first, 'cos I am crap at welding UP wards

But it could happen, at present though I have added stiffening webs off the boot floor alongside the U channel

I think it'll do for now

The lower shock link bracket seems OK to me, I dont rally Lara, but Paul is right about the mini shock when in use as bump rebound, not properly up to the job 'cos it's too short. That is why the upper channel failed I believe

I may put the old levers back on, they worked.
bill sdgpm

Bill

I repaired one of the floating upper mounts I referred to with a couple of through bolts, 3mm plates to spread the load, as extensive udersealing had turned a welding repair into a major. Worked fine for the check strap application.

I dont recall seeing a pic of how you have reinforced it, but what about a similar approach using a top plate about 4x3" but weld around the edge of the top plate which would be nicely accessible inside the cockpit and you'd be welding down, not up. That way it would spread any upwards bump loads over a good area (and also into the chassis rail as one side of the plate would lie alongside it)
Paul Walbran

In this picure you can see the bracket addition I blobwelded in place to hold the shock upper end.

I'm not even slightly tidy welding uphill as you can see

I would like to whip the U-channels off on both sides and Paul's suggestion strikes a chord with me, could be the way I go

But for now the bracket is sitting still and behaving, though it gets looked at far more often now.

MOT in a couple of months I'll see if THE MAN thinks its OK then

There's a large diameter washer welded onto the other side of the bracket to prevent cracking re-occuring, yes it cracked that side too, which is why I have a "plan A" for that entire section

bill sdgpm

Sorry Paul, But NOT!!!!

If your argument is logical, then hip hip horray we can now all use 10, 20, 30, heck Unlimited number of flat washers as wheel spacers so long as the wheel stud dosnt bend ... Just put them between the hubs and the wheels and run longer studs thur them...Or in keeping with your argument when can just use PVC plastic plumbing pipe with just a flat washer at both ends to spread the load of compression and get rid of the flat washers... Thanks Man that solved several problems Im playing with...You do the 1st high speed test drive into a hard corner okay, ill run the video cam...LOL


you said ....
>>>>>>>Increasing the length of the mounting bolt as he has done will not change the shear, as SHEAR on a canilever depends only of the load and the cantilever section and is independent of the load position. <<<<<<

(yeah Im not buying that)


think of andrews tube set up as a swimming pool diving board... If a 600 pound fat kid dives off the end of a normal length diving board, its gonna bend, you put an 5,000 pound fat kid at end of the diving board its going to break, and its going to break not at the end thats unsupported but where the board is mounted....now take that same board and make it 1000 feet long and put the 600 pound fat kid at the dive end ... did it break, Im sure it did, now make the same board 6 inches long and put the 5000 pound kid on the end... did it break ... probably not.

Apply the same principal to andrews flat washered tube design... removing the washers and shortnening the bolt is the same as making the dive board 6 inchs long. the washers are filler only and provide no structral support just filler, in addition making a proper spacer that makes the 3 joint(3 parts of the tube design)into a one whole single piece instead of 3 peices will make it stronger and Bend resistant

In my world when something is bending, it means something is wrong ....get out of the way


Prop.


Prop

Sorry Prop if you don't know much about stress analysis, we have a household full of qualified engineers here and they all agree the shear stress doesn't change. Your diving board analogy confirms you are thinking about bending which is defintely not shear. That is the very point I was making - bending is the issue here, not shear.

When something bends, one side stretches the other compresses. If these bending stresses exceed the tensile or compressive properties of the item you have trouble. The washers will have good compressive properties if they are properly tightened, not as good as a solid spacer for sure due to surface irregularities, but in this case my pick is that suitably pre-tensioned they would be well up to the relatively minor loads involved (provided that the shocks are doing damping only and not acting as a bump stop)
Their tensile properties are just as good as a solid spacer - both are zilch because neither are continuous the mounting bracket. If they were welded to it, yes there would be a tensile contribution, though the welding process produces undesirable stresses of its own.

Extending what I said to absurd extremes as you did doesn't help either as the comparisons are not apples for apples (eg PVC plumbing pipe has nowhere near the compressive properties of steel)

The big problem you get when cantilevering things out is often not the strength of the cantilver itself, it is the strength of what it is attached to and other downstream effects. That I suspect is the case here and going to a solid spacer won't change that at all.
Paul Walbran

well we do agee (I think) that if the shear is rated at 500 ftlbs ... that is a continouis fact that will never change its manufatured into the bolt.

but I have to disagree with you that the length of the bolt and the amount of wieght on the bolt does not influence the constant 500 ftlbs shear

As an example recently I had difficulty un doing a bolt on a crank shaft pulley I started with a reg 18 inch long wrench, we finished with a 10 foot cheater bar and 2 large men pulling like mad... the point is the break point of the crankshaft bolt was always constiant, it never changed, what changed was the perception of what the bolt was feeling meaning .... the 2 large men applying pressure needed to apply far less pressure to the 10 foot cheater... maybe 600 foot pounds if I was going to I loosen the nut with the 18 inch long chater bar it would have taken me 600 ft pounds X 100s to accomplish the same feat


what im saying is the shear breakage point is the same on that bolt of andrews tube shock no matter what ... But the length of that bolt can influence how much wieght is needed to shear that bolt off at the mount,,, the longer the bolt and the futher out the weight ... then the less weight will be needed to shear the bolt at the mount

You got me on the washer argument ...the washers being compressed togather and held by friction Is an interesting dilima... I can see the point and I sorta concede that the added friction of the washers against the mount may increase the level of shear strength the bolt needs to go pop... but in my heart of hearts I still dont want to ride in andrews car in a hi speed sliding turn with those washers used as spacers... and welding the washers togather Id think illrealvent you still have a pile of washers making up one part of a 3 part contraption... if the contraption has to be cantilivered then it needs to be made into one part instead of 3 parts granted you are making a one piece thur friction. 1 the shock, 2 the bolt, and 3 the mount that the bolt is screwed into

If it where me Id make a lipped bushing with extrenial thread and internal thread ..run it thur the tube shock and thur the mating hole on the other side of where it mounts and make the mount screw hole longer, then screw the bolt thur the lipped bushing thur the shock into the mounting hole and make the bolt longer then the theaded bushing... that way you have No Single shear points that Deb evans made mention of.

Sorry paul... even tho you got me stumped on applying friction to the washers, I still have to dis agree with you and say Andrews tube shock conversion is not safe,,, it might be something you might do but not me.

Prop
Prop

Oh I got you Paul on the flat washers!!!

What if the bolt works even a small bit loose... what will happen to the friction built up in all those flat washers?

Yeahhhhh...LOL

I hope andrew remembered to use some red locktite when your driving thur the country side with him flying around dirt curves with jagged 100O foot moutian drop offs just outside your passanger window ... LOL

Prop
Prop

You are still confusing shear with things it isn't. The crank pulley example is all about torsion, again something different. This is not to say that your analysis is necessarily wrong, just that it is not about shear.

Your comments on Andrew's set-up express concern about bending stresses, not shear - and I agree that ultimately failure if it does happen due to high loads or extending the load application too far out from the support will be due to bending.
I just don't think that the load and point of application will be a problem here.

I haven't done the numbers myself, Andrew says he has and from what I can see I can't see that he'd be wrong. OK the engineering could be a lot neater, but it was a prototype to prove or disprove the point and I don't see anything wrong with a temporary rig for doing that. (Andrew said he was working on the permananet version )
Paul Walbran

Your diving board analogy confirms you are thinking about bending which is defintely not shear. That is the very point I was making - bending is the issue here, not shear.

Hmmmm, (wheels are turning)

Well I hate to sound like a total idiot, but what is shearing? and what is bending?

In my uncouniose preconcived notion (meaning ive never thought about it before)

I would have thought they are the samething but one is the horse and the other is the cart

they are both acting to stress it would seem that shearing is just a more violent form of bending, or maybe benidng is just a slower motion of shearing

then there is the whole melacular thing where in shearing you have a force that would be compressing the melacular stucture extremely tight making it rigid like glass

On bending the stress is built up over time making the molecules on one side of the universe tight and rigid,, but on the other side of the universe they would be relaxed and spread out... thus the bend


Am I even in the same ball park...

Umm you said your a engineer,,, real or just play like me..LOL. if your not Im going to look like an idiot.. with this posting LOL


If your are a real engineer... my apologies for questioning you, Im clearly missing something.

Prop... No dis-respect intended
Prop

okay so shearing would be like a paper cutter with a big long knife hinged at one end and it slices thur the paper as you pull it down thur the paper... your seperating the molicules with a vilont force, creating 2 haves instantly


and bending is like like folding the paper in half with a clean crisp edge on the fold... so what is the molecules doing in the paper fold? are they doig like Im guessing in the last posting

wow....what the heck does that mean as it relates to andrews tube shock? to make shear as where talking

Paul Thank YOu, Ive been needing a good brain puzzle

Okay so how does shear happen? is it a 2 part force... in other words you have the contraction of the moleculs and a 2nd force that seperates them

or perhaps the molicules DONT contract and become rigid... perhaps they stay loose and get pushed to the side

So what the heck is shear?

Sorry if Im behind... typing in one on one form for comuniction is difficult
Prop

OMG... googling shear and bending is some mind altering freaky science, I had no freaken clue it was that complex

JEz talk about taking words for granted... who knew there could be so much to shear vs bend

If there is one thing ive learned in the last 2 years on this board, if you really think you know something...then your as dumb as a box of rocks

when I was 18 I knew it all, Now, Im surprised I can recognise my own name.

Thanks paul...I got a new challange for the brain to play with
Prop

Prop

I think you've tied yourself in one big knot there.

Bending theory can be very complicated or fairly simple. I'm a dumb bridge engineer so I try to keep it simple ie I stick to elestic theory and generally ignore plastic issues unless really necesssary. I'm sure a decent mechanical engineer can prove it will work to far more decimal places than I can.

I did the numbers using simple elastic theory at ULS I used a gamma fl of 10 to simulate dynamic effects and the tensile stress in the grade 8.8 bolt was about 1/5 the characteristic value (I used 830 MPa as a rough lower figure) and compression in the small area of the washer was about 1/4 of the characteristic value(I used 275 MPa as a rough lower figure)- I'll sleep at night - deflection was not a problem at <0.1mm without any pre-tension in the bolt.
I didn't even worry about fatigue as it's not likely to get anywhere near enough cycles before a permanent fix.

Andrew Dunn

just to be referee between prop and andrew for a min, can i point out whether it bends or shears is irrelevant isnt it?, neither is good for the car or the driver. if it shears its bad and if it bends enough times then it gets metal fatigue and still ends up breaking. DING DING SECONDS OUT ,ROUND TWO!!!
roy j

Most parts of the car are bending or shearing or somehow changing stress and strain as they either sit still or move along - if the material stays elastic then this is usually fine. Other factors come into play with age - fatique, loss of section due to corrosion + others - but these can all dealt with by maintenance/restoration.
If steel in particular goes beyond its elastic range then it becomes plastic which is fine in certain circumstances (eg. some head bolts) but generally not a good idea for the bodyshell.
Andrew Dunn

"whether it bends or shears is irrelevant isnt it"

Not really. In order to know whether a component is up to the job you need to be able to calculate the various stresses. Shear and bending actions behave quite differently in how they generate stress, so you have to examine both. And torsional stress if twisting is a relevant consideration.

Roy is right to the extent that if you get it wrong and it fails, the result is a broken component for what ever reason.

However, as Andrew points out, everything in the whole car is bending, shearing, twisting etc whenever a load is applied. Examples: flexing in the bodywork (very noticable in a convertible)- designed to be rigid as possible but it still deflects a bit over bumps etc,
road springs - designed to deflect a lot, that's their job. But there are limits to a springs elasticity ... remember the rubbish spring steel of 2 or 3 years ago?
1/2 shafts - hit a nerve here with Midget owners - not the strong point of a Midget, but thesy still take a lot of flexing before they finally give up. The Growlerising process actually ends up with the 1/2 shaft flexing more than standard, but as the changed shape results in a much better distribution of stress they last longer.
crankshafts - subject to minute trosional delfections with each power impulse. (Ever noticed those bonded rubber crank pulleys? They are torsional vibration dampers.)

And the list could go on and on.

Provided deflections are kept within accepted limits, the component won't fail prematurely. The two ways of doing it are the "brick sh*t-house" approach, or to design the component within accepted limits allowing for recognised safety factors. The first approach is not all that good for power-to-weight ratios, if we use the second we have to be very careful we have the maths right!

Final thought:
Ever seen the wing deflection in a 747? Up to 14 feet I understand. One enormous long cantilever flapping about with large deflections for hours on end every day of the year. Now that IS scary if you think about it, but they are designed to do that and we all still fly in them!
Paul Walbran

Dug out this info about standard mini front shocks when I was sizing up mt mod:

In the fully compressed position - 210mm between centres.

Fully Extended - 330mm between centres.

These seem to be lower then the spax values above

Also, the top mounting on the 1500 shell looks to be different to Bill's - the hole for the original strap is sleeved through the box section suppert member - there is no U section - or did you cut out the box section to form a U?

Not a great picture but you can hopefully see why I had to use the spacers.

Andrew Dunn

My mini front type ones are mounted as Andrew's at the top, but are angled slightly outwards to meet the bottom spring plate bracket without use of a stack of spacers - just a pair of large penny washers. But mine do have "metalastic" type bushes top and bottom which allow for this slight splayed effect.

Guy
Guy Weller

Hi

Quite a few years ago i owned a Ford Anglia 105e, it had the same dog-leg shocks fitted to the back (Mcpherson strut at the fron i think)..
My dad knew someone that could get replacement (new) dog-legs but didn't know the designation for my shocks and asked if he could take one of mine to match them up..
I removed the ns rear and my dad dropped it in with him, it was a week later when i got the new shocks and fitted them...

I had used the car daily on three shock absorbers and could tell no difference in the ridequality, could this be because the 105e wasn't a performance car in fact it would struggle to pull you off the karzi!!!!

I suppose it could also have been that the shocks were knackered anyow and the removal of one wasn't noticed due to that fact, when i fitted the new Armstrong units, there was still no discernable difference (don't you just hate it when you do a job and there seems to be no improvement!)...

I daresay that had it have been an E-type or a Jensen intercepter with three shocks that was being pushed hard, i would notice the difference in my undercrackers!!!!!!!!!


John :-)
j b biggs

This thread was discussed between 06/05/2010 and 09/05/2010

MG Midget and Sprite Technical index

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