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MG MGB Technical - Rear shocker rating

What is the rating on the rear shockers?
Actualy I'm not even sure how shock absorbers are rated. Can anyone inform me?
The reason I ask is that I am looking at fitting pnumatic shocks and I have read that the spax shocks are too hard even on their lowest setting (what is their lowest setting, by the way?). And this from people who have just spent alot of money fitting them and are unlikly to admitt they've done their money. 'Way way too hard' would probably be closer to the truth.
Why not keep the existing?, because this is going to be part of a three link trailing arm coil spring set up. Getting coil springs to fit up into the orrigional locations is turning out to be very difficult. Space availiable is;
Ride loaded (400lbs) height 5.5 inches, Solid height (max')- 2.75 inches, free height(min') 9.5 inches and therein lies the problem. fitting anything up into there will have a very high spring rate and is unlikely to be much of an improvement. So I'm having to look at coil over shockers (which aren't cheap) and I want to get this right. I'm thinking that if I bolt up to the current shocker locations I'll have plenty of room, with the advantage of being able to adjust the ride height if it isn't perfect. It also makes setting up this three link much easier, which it should given the cost of coil overs!
Ratings anyone?
Peter

Dampers have a ‘damping characteristic’ a value between 0 and 1 (ie .35) sometime referred to as a percentage (ie 35%). The ‘damping characteristic’ is also frequency and applied force (load) dependant as a ‘mass/spring/damper’ system. Car designers and manufacturers spend many hours of both engineering design and subsequent testing to ‘tune’ the dampers to the vehicle.

The over damping often referred to regarding the MGB is due to the cumulative function of the tube dampers and the damping provided by the leaf-spring inter-leafs. The frequency characteristics are also different between the springs and the tube dampers adding to the problem.

All that said, there is no doubt that the tube dampers provide better damping. I recently dyno-tested six leaver arm dampers from Moss, and not one was satisfactory. So I too have gone for GAZ dampers all round.

The damper compression values for road cars should be between 30..50% of the re-bound value, to avoid ‘reverse jacking’ under breaking or acceleration. The adjustable type dampers like Spax and GAZ give you the opportunity to tune the dampers to your car, with a fixed bump-to-rebound ratio. So my advice would be get ‘adjustable’ dampers and ‘tune’ them in yourself as your car will be virtual unique.

Two final points, for road use; over damping is bad ! under damping is OK, don’t go too hard.

Lastly, to be correct, the shock absorber is the ‘spring’ part of the mass/spring/damper system, what is often referred to as a shock absorber is actually a damper! Even the manufactures of this thing get it wrong. I hope that helps.
MG Mike

Mike - were these recons or new lever arms, and what did Mr Moss say? (you did tell them didn't you?!)
Dave Smith

My V8 came with adjustable Spax and a teeth-jarring ride, I had to put them onto their softest setting to get it acceptable. Then one of them started leaking oil and I had to replace both - at a cost of about 10 times a single recon lever arm. Then several tens of thousands of miles later I become of the rear getting softer and softer and bouncing when going over speed-ramps etc. Attempt to stiffen them up only to find the adjusters are seized. At that point I go back to standard lever arms, and some consistency. Comparing the Spax and lever arms off-car the Spax are extremely easy to move. Now I have the Spax off and they are junk I attack them with hammer and releasing fluid and do manage to free the adjusters. I find that whilst the adjusters do add some stiffness in one direction (possibly compression) they are still as soft in expansion, and much softer than the lever arms.

Conclusion? They are junk. Unless you are going for a wholesale redesign of the rear suspension tubular dampers are a pointless expense, and even if you are my experience is that they are very inconsistent. By comparison lever-arms seem to work consistently until the seals fail and they start leaking hydraulic fluid, at which point replacement is no more than a few quid. Yes it's possible to get a poor rebuild that fails withing a few thousand miles, but they are cheap, and I have only ever had one like that in two cars over 15 years and 110k miles.
Paul Hunt 2

Dave, yes I returned the *new* 25% up rated dampers to Moss with the results from the dyno test (we have one here where I work, very handy!), I must say that Moss were very helpful in supplying numerous replacement items (albeit none of them any good, not a matched pair amongst them) but they did refund my initial payment and came and collected all of the duff units. A familiar story with Moss, good service, but the customer (me) is doing the QA not the supplier!

I do agree with Paul’s post above too, the Spax dampers are junk, not only are the dampers of poor quality, but the installation is not as good as the OEM leaver arm set-up, all due to the drop links in my opinion. GAZ dampers with spherical bearings have both the required damping rate and the lateral articulation to work with the MGB suspension geometry.
MG Mike

MG Mike,
Would you please contact me?

Peter C
Peter Caldwell

Thanks gentlemen,
For the futhur warnings about SPAX and inparticular for the information on GAZ shockers Mike. I haven't read anything bad about these yet. I found that GAZ also sell coil springs to go over their shockers and these might just be the ones to buy. What type did you buy? A quick perusal of thier site seems to indicate that most of their shockers can be fittted with coil springs. For your hardness setting, have you dialed these right down or is there still some way to go Mike?. I noticed reference to a fitting kit on their site. Is that what you used? Do you think that this could also be used for a coil over set up? This would certainly make setting up this three link very very easy if true. Does the bottom end of the shocker bolt up to the MG spot?
Any idea of cost? How long to these tings last do you think?
Paul- although I tend to think that there is nothing too much wrong with armstrongs (at least the 30year ones I've got, good value) Trying to get useful coil springs short enough for the orrigional location is nearly imposible and coil overs are the answer. I was hoping to get some short progressive springs, which would be ideal, but so far no joy. Minimum so far is 100mm solid. If you look at ordinary springs you need to go soft in order to get the supension travel ie <100lbs. Soft spring with about 6-7 coils total and 2.75 inches of availiable suspension travel doesn't sound too good to me!.
Peter

Peter - I'd agree that a major redesign of the suspension would almost certainly do away with the lever-arms. In some cases it is one of dynamics because the original multiple leaf springs have quite a bit of damping effect on their own and so the lever-arms are only designed to bring this up to the required amount, whereas the single leaf springs have virtually none and so need stiffer dampers to achieve the same effect. In others it is probably one of sheer practicality and space limitations as you say. Personally after my experiences with Spax I wouldn't even bother trying anything else like Gaz with an otherwise standard setup, there simply isn't anything to be gained. And it may be that you would actually lose, as the Armstrongs have a 2-stage damping process, with short gentle movements as on a pretty good tarmac surface having less damping and so giving a smoother ride, with stiffer damping occuring surfaces giving faster and longer movements. I've not *heard* of this being the case with any tubulars.
Paul Hunt 2

While I agree with the fact that Spax are a bit too hard even at their softest setting on the back of a B, I've never had any problems with quality, [touch wood] I've had them on the back of the B for 10 years and all round on a TR6 for 5 years without problems. Actually either I've got used to them or the Spax have softened with age but they doesn't seem all that bad now on the back of the B.
I think the problem with the rear of the B is the additional damping of the leaf springs because the problem doesn't happen with the TR6 which has coil springs, and the Spax are quite comfortable on it at about 1/4 way up the settings.
Ron
R. Algie

Actualy I wish I could keep the armstrongs, the main problem with them seems to be poor quality control on rebuilds in many cases. Nothing wrong with the orrigionals I think. My current set now have 31 years and at least 85 thousand on them and they are perfect. When I bought the car I topped them up with oil (the access holes had been painted shut so it had been a while), but they didn't need much.
However from your, and Rons, remarks I gather I actually do need to change shockers if I dipense with the leaf springs, which is reasonable. That makes me feel a little better about the additional considerable cost. Plus the GAZ seem to be pretty good.
Peter

This thread was discussed between 21/07/2006 and 24/07/2006

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