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MG MGB Technical - Composite or parabolic rear springs
I had in mind for quite some time to do something about the rear suspension of the MGB. I've had fun working out all the details however before I go off and spend a couple of grand on non standard bits like coils, (possibly coil overs) exhaust replumbing, trailing arms, engineer certificates etc I think it would be senceable to look at the off the shelf alternatives that will not compromise the car and might infact be cheaper.
The light weight composite springs (and anti-tramp bars plus panhard) seem to fit the bill. They would be a lot lighter and so much more responsive. At the moment the Australian dollar is strong and now might be the time to buy them.
I've also heard recently that you can get flatter arch composite springs (fiberglass) that will adjust the ride height from rubber bumper to chrome height. Something I wasn't aware of previously.
What do people know about these, pros, cons?
Where can they be bought?
How much can I expect to pay?
Also I've heard a little about parabolic steel springs. Are these really any lighter or better?
Can they be got in a flatter arch?
Where can these be bought?
This is a V8 by the way.
I'm using MGOC parabolic rear springs on my 1978 MGBGT, which has an Rover V8 in it. All seems to work pretty well. You have a choice of springs from the MGOC - chrome or rubber bumper for a start - and I think there are lowered ones availble, too. The fitting kit also allows you to 'fine-tune' the ride height by putting spacers either on top or below the axle.
Personally, I'd contact Roger Parker at the MGOC and ask for his recommendations as to exactly which springs, by part number, to use. He's one of the good guys and is aways happy to advise.
I have a V8 Roadster which I fitted with steel parabolics,adjustable shocks and anti tramp bars - different car (for the good !) and a slightly harder ride -it pays to check the nuts regularly -as they tend to loosen on the bars , I run 185/14/ 70 tyres with 4 pot calipers onthe brakes but the best thing for roadholding etc is 4 new tyres !
|I've heard of composites fracturing in heavy use, something which shouldn't happen to parabolics. Since the standard springs are the only thing that hold the axle to the car I certainly wouldn't want to use composites without positive fore and aft and lateral location. Both require telescopic dampers with more damping action than the standard lever-arms.|
|Paul Hunt 2|
Parabolic spring are by far the best to have. Doug at MG motorsport can change the shape of the springs to the best ride hieght.
You should be able to find his website, the springs are around £300
Last time I spoke with Doug at mgbmga.com, he was not sure if composites were going to be in the works anymore. I would contact him and see if there was a chance that something was going to happen or if he has sold the line to another supplier. Personally, I really like those.
Second- I have heard but have no experience with teh parabolic springs. I would like to get the chance to experience these at some point.
There are also IRS setups manufactured in the UK and fastcars may have something as well. Don't recall what it is off the top of my head.
Bill Guzman of CCE ( classicconversioneng.com ) is almost finished with his suspension setup which may also interest you.
|BMC Brian McCullough|
|Thank you for your replies all.|
I checked out the site at British Automotive http://www.mgbmga.com/
and the composites were listed, but under the category of “finding a new supplier and I can’t get through to Doug on email email@example.com <firstname.lastname@example.org>. Various other composite spring ancillaries were still being sold. I will have to telephone him some early AM. The MGOC had composites listed, but no price or other information. I wonder if they were getting them from Doug.
As an alternative, I would imagine that the parabolics would have to be far more responsive than the standard springs. Going by appearance, I would guess that they would also be about 2/3rds the weight of the standard 6 or 7 leaf springs. I shall certainly get those if the much lighter composites aren’t available. Apparently Doug has sold around 80 pairs of these so they are past their ‘trial period’. Mind you if he has stopped selling them they might have failed the test and this is the primary reason for my post. I might also post a question over on the engine conversion thread.
I would like to try the Armstrong shockers before going to tubular. I can’t see why armstrongs in good condition would not be as good as tubular. Reduction in un-sprung weight is one of the main objectives of this exercise and Armstrongs are excellent in that respect. Mine are in good condition. You can also get 30% stiffer armstrongs or use a heavier weight fluid if that is an issue. Some of the silicon oils might also be a possibility. Something with a constant viscosity over a wide temperature range. I had a hunt around the archives and the main articulated objection to them was that the armstrongs would over heat with the more responsive spring and boil their oil. One person tested this out and found that they didn’t, because he believed that the car was acting as a heat sink. This heat transfer effect could be much amplified by making a good thermal contact between the car and the shocker by removing paint and simply bolting a largish, thin piece of aluminum between the shocker and the car. Plenty of room under there. If in fact it becomes a problem, and I can always change to tubular later on if it is a real issue.
Setting up a three link trailing arm and coil springs system is not difficult to do. The key to it is the upper link. I had planned to bolt a bracket to the top of the Diff’ housing. The bracket would have a section that hooked over the back/top of the diff’. The Salisbury diff’ is slightly more than one quarter of an inch thick (at the thinnest) and even has a flat spot on the top , a little to the right, which is ideal. A single large bolt with a large thick plate/washer coming up from inside the diff’ would hold it all together and the ‘Hook’ would distribute acceleration forces evenly over the entire back of the diff’. A couple of pieces of steel bolted in and around the top right of the transmission tunnel would take care of the body end.
However, you must then ask would I be saving any un-sprung weight? The third arm, brackets and coil springs would be heavier than the composite springs and possible even the parabolics. The tiny amount of weight that you might save is simply not worth the expense and effort. Unless of course you simply want to try something different.
A true IRS (like Hoyle or Jag’) would reduce the un-sprung weight certainly, and make for a much more comfortable ride, however at the expense of adding sprung weight to the back of the car. The weight distribution in the MGB is exactly 50/50 and I don’t want to change that.
Yes, there were some composite springs that failed but most worked well and the reasons for the failures was diagnosed to the best of my understanding. Doug is retiring and last I spoke to him, the supplier of the springs was so slow that he was looking for a new supplier -IF- I remember correctly. It was not that they were bad. I have two more pairs to install. One for a client that is supposed to be in here next week (they have been waiting for quite a while!) as well as a second pair for my own car. I still need to purchase a set of antitramp bars from Doug or the new supplier before I install these. I am going to install all this on a narrowed GM axle in my MGB.
|BMC Brian McCullough|
I have had parabolics on my CGT from the moment the MGOC introduced them (3-4 years ago?). Much more confortable than the originals. Last year I changed from telescopic dampers back to Armstrongs (on the advice of Doug at MGMotorsport). On my car the tele's weren't very good at absorbing small bumps, levers are much better. I know some people swear by their tele's, I would say: try the levers first , If you don't like them change to telescopics. There is no NEED to use telescopics.
BTW, I use heavier oil in my levers, but that is against Doug's advice (and I fear he might be right and the set-up could be even more comfortable).
What I have noticed with the paras on track days is that I think I can feel the rear axle move sideways a bit in really fast corners. Can't remember if it was the same with standard springs an have been to cheap to buy a panhard rod...Something to consider.
Good luck in deciding,
|This is good to hear Rufus,I'll go in stages.|
The Armstrong's are unfairly criticized I think. They are a very clever solution to reducing un-sprung weight. The second most important function of shock absorbers. Kudos to Mr. Armstrong. Who ever he was. It's just that most of them are 40 plus years old and even the most mediocre replacement is going to look better then. So long as they are 'as new' and both bushings are good (not 40 years old) then they must be better. After-all one link and half an arm is better than the weight of the entire shocker.
It is a pity Doug is letting it slide, I would have thought the business would be worth selling. Anyway I'm buying one or the other and I'll let people know.
|Paras do have a wind up issue with a V8, composites need helpers, there is no perfect solution, but probably with the dosh Hoyle IRS.|
Doug prefers the rear axle movement.
I recently fitted a pair of reverse spring eye 110lb rear leaf springs to my rubber bumper GT MGS40721 from Moss at £146.00 per pair 93lb available for roadsters.
This was initially going to be an interim measure as the intention was to fit a Jag IRS but I am so impressed with the new springs I may not bother.
Moss state that the springs are made to a far higher spec than the usual offerings, and that the spring rate and ride height will be correct and I can confirm that having fitted the springs that they were telling the truth.
I retained the telescopic dampers that were part of the original Moss handling kit, Gabriel non adjustable which we tested and found to be in good condition and have an acceptable damping rate, we removed the rear anti roll bar which I felt was causing snap oversteer especially in the wet.
The outcome is that the car now sits 2" lower, the rear suspension now works, the ride is very acceptable and the transformation in handling and grip simply amazing.
I only recently had the opportunity to try it out on a quiet country road and through some fast bends the car just sat down and gripped and inspired confidence, which is something it didn't do before with the old rigid springs.
I'm also using a 7/8" front anti roll bar and the balance front to rear feels very good but currently no anti tramp bars, and with fairly spirited starts the rear springs seem to be able to resist wind up and tramp, althought I may consider fitting a tramp bar kit with mods to alleviate the conflict between the springs and bars in bump situations.
Hope this is helpful.
I intend to fit antitramp bars and a panhard rod. The local hot rod guys will make up bushed or rose joint links for around $110 each.
Well it looks like Doug has really retired,
I can't get through on
Telephone: 001 (415) 472-1493
and email@example.com <firstname.lastname@example.org> comes up un-deliverable.
Can any of you Americans see that I'm dialing something wrong? Leaving an area code out or something?
Its a pity, I'd like to have got a set of low arch or even standard composites from him, he really seems to know what he is doing. However if the man wants to be left in peace, that's that. It's a pity he didn't sell the business to someone.
I'll try the MGOC tonight. The exchange rate is a bit of a killer though.
Brian, from what I can gather even the standard arch composites set the car about one inch lower than standard steel springs. Is this true? I have lowered my rubber bumper car at the rear by a combination of re-drilling the forward spring hangers and using one inch blocks. If in fact the standard composites are already one inch lower than standard then I would be better off getting those, throwing away the blocks and keeping the use of the re-drilled hanger hole. The original hole would make for a neat antitramp bar bolt on.
|Most times I see a US number written compatible with Euro or UK phones it's rendered +1.415.472.1493 (or would be in this case) The (415) area code is analogous to both the country and city codes. The initial "1" would be your access in lieu of "0" - or so I think, it's been a few years since I've been in the UK. I do wonder if you're punching an extra zero or two. From our side of the Atlantic, we'd start off with 011 for "international" and then 44 for the UK (if I recall) and then dispense with the normal "0" and call the number. |
this may not help - but what you've got isn't working that well either.
From here, international calls can be prohibitive if you don't have a plan that covers them. To avoid a nasty surprise, you might check with your provider.
I would be very wary of fitting a standard anti-tramp bar kit as this could still overstress a composite spring.
With composite springs you are very much in a catch 22 situation, if you don't fit anything to control axle tramp the springs will delaminate with disastrous results, I've even seen parabolics twisted into a figure S by the torque applied through the axle.
The problem with atandard anti-tramp bar kits is the conflict between the spring as it lengthens under bump and the fixed length of the bar.
If you have a look in the V8 conversions section there is a thread explaining what simple mods are required to avoid this and maintain suspension compliance.
|I meant to post a couple of pictures of modified anti tramp bars. Personally I favour the bell cranks that pivot from the right angled locating hole and pivots on the front spring eye bush locating bolt.|
|I thought I'd pipe in with my experiences. I had a set of composite springs on my B for a while - until the dreaded day came that I wrapped them up and shattered the right side. They were NOT from Doug though - I understand his were less likely to do this. The manufacturer of mine did some small batch work, but never produced very many. |
I now have the steel parabolic springs fitted with lowering blocks and they perform extremely well. They're not as smooth and responsive as the composites, but they beat even the best set of stock type springs. I'd guess they're only lighter by 10 lbs (5 kilos?) per side. They make tube shocks tolerable, but I plan to go back to Armstrongs from Peter at World Wide Auto Parts(peter at nosimport dot com) since his re-manufactured shocks are better than any new or rebuilt shock on the market - period!
|Well Ive been using Composites for the last 7 years|
and doing about 10 trackdays a year.
I can be absoluteley brutal throwing all of the 314 ft lb of torque and 282hp in full throttle launches from the tuned 4.6
Handling is superb.
There is not much left of my car that is standard and I believe the composite springs to be the most important upgrade of them all.
To hold everything in place Ive made some anti tramps and a panhard rod with a small rear ARB.
I know some one with a 4,6 GT and he has snapped 2 springs each on the thickest part in front of the axle.
My theory is that the anti tramp bar geometry is at fault.
Passenger ride anyone?
|Mark - that's where mine broke is on the RH side at the thickest part at the axle and forward about 6"s. In my case I was foolish enough to run wihtout anti-tramps, but I only have 90-ish hp at the rear wheels. They broke during normal street use - no track time.|
|Thank you for you contributions folks, |
It looks like that these composites are able to do the job, when they are on spec'. They all need antitramp bars. 'm fitting these anyway. I'm very concerned to hear about the set that broke with anti tramp bars. Did you have a chance to see if these were the usual solid body bracket RV8 kind, or the sort that load the front of the spring Mark?. On Dougs site he warns against these.
Specification issue- even Dougs (which have the best reputation) had a +/- 15% variation in spring rating. That implies pretty serious lack of control of the maufacturing process. They should be putting exactly the same glue impregnated material in exactly the same sequence into a heat pressure mold and baking it, such as they do for formula one carbon bits. If this is so they would all be very close in rating. The stunning price reflects this!
Un-fortunately the +/-15% (total 30% variation!)reflects that these are likely laid up by hand using brushed on epoxi by people of varying skill person. Even if you were saturating single direction S glass and then laying it in a pressure mold you still would not be getting that sort of variation.
Basically, if you get a good on spec' set they are fantastic. Problem is that there appear to be lots of marginal springs, that might have used a bit too much, or not enough glue on the brush, or the epoxi started to go off too soon because it was a hot day etc etc..
That's sort of OK if you are using them once in a while for racing. Break them, replace them.
Not alright for a daily driver.
It might have to be the parabolics. Standard springs weigh 20 pounds. Parabolics appear to be half that, which is pretty good. Thats 10 lbs more than parabolics but 20lbs less than standard. Plus of course, they have no interleaf friction.
They don't sell them here. Can anyone suggest a good supplier in America?
The exchange rate is a lot better than England for Australians.
I'd probably try a set of those armstrongs that Jeff mentions as well.
|oops, that should have read, 10 pounds more than composites, 20 pounds less than standard.|
|Peter Yes it was the solid body mounts.|
If you go for the solid mounts I would advise a geometry check is done. Basically measure the distance between body bracket and axle bracket throughout the expected suspension travel range. If this distance changes then some interference and binding will occur.
|Yes, I'd say that the distance between the spring (eye and axle end) and the antitramp bar mounting points (depth of bracket) is critical. The spring is a curved surface and the antitramp bar mount points are right angles to that surface.|
When the curved surface of the spring becomes more curved the right angle to the surface antitramp mount points will rotate away from one another. When the spring straightens, becomes more flat (and become relatively longer the antitramp points rotate toward one another.
The must be a way of mathematically expressing this.
To begin with the antitramp bars must be the same length as the "spring eye to bolt". The depth of the bracket would have to be some function of the length of the spring. My maths are not good enough to work this out!
Any one want to hazard a guess, is is it just trail and error. Perhaps Mark would tell us the depth of his brackets? axle perch to antitramp eye and spring eye to antitramp eye. Herein known as the anti tramp "bench MARK" (ho ho)
Big ask Mark, but given the amount of torque you are putting through these things, you must have hit the nail on the head. Luck or talent?
|Currently no one in the US carries the steel parabolic springs. The MGOC in England seems to be the only place you can get them.|
if you are going to order the parabolics from the MGOC, don't bother with the "free fitting kit". I got the yellow bushes with mine. They started squiking after about a month, never was able to lubricate them often enough to have a quiet ride. In the end, after > a year, I changed to Superflex. Axle and springs are located better and everything is quiet again.
|Moss do parabolics. part no tmg40740 at 100lbs for chrome and tmg40741 at 116lbs for rubber bumpered cars. uk price is £109.94. Jim|
If you intend to go ahead with the Parabolics,I would recommend Moss rather than MGOC and make sure you speak to someone who knows what he's talking about re; springs and ride height, there have been a lot of Parabolics made to the wrong spec and ride height and a lot of customers who have gone through several sets.
My friends chrome bumper roadster on Parabolics from MGOC now rides at rubber bumper height ie 2" too high, make sure they can guarantee the springs will be correct as you don't want to be taking them off the car and sending them back especially from Oz.
I am thinking of buying a set of Parabolics next time I'm in the UK (Moss is only 10 minutes from Heathrow airport using airport transfers sevenoaks).
Does anyone know how much a parabolic spring weighs?
|Jeff estimates about half the weight at 10 lbs each.|
Thanks for the warning Kevin. My bolt on three link is starting to look good again.
This thread was discussed between 21/11/2007 and 15/12/2007
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