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MG MGB Technical - Rear Spring & Damper Upgrade

After trying combinations of new leaf springs, parabolic springs, SPAX dampers, new leaver arm dampers, I've settled on a combination that suits me and my car.

I've made some new leaf springs, interleaved with nylatron and fitted new modern dampers.

The 'kits' for the SPAX dampers, hold the damper at an angle, putting a high load on the seal, so they don't last too long and perform poorly, often too stiff.

I believe the MGB feels better on the road with softer damping, similar to the original leaver arms, but the modern dampers are evenly matched, dyno-tested and provide consistent damping with temperature and over time. You do need to mount them correctly, so a made some new mounts too.

I also had to fit new spring hangers, in order to centre the rear axle, after measuring seven axles, no two were the same!

Car now feels exactly how I wanted it to, a total joy to drive.

For information, I've uploaded some drawings and photos to www.d2sys.co.uk.
MGMike1

Wow! You must be a very handy fellow. It makes some of us other fellows feel a bit inadequate! You've don a great job. Mike
J.M. Doust

Very interesting, I too have been playing but not to your degree. What did you think of parabolics? I look at the club ones and can't say that they inspire me.
Why do the telescopic kits always mount them at an angle? I've always assumed there must be a good dynamic reason to do with the arc of the springs movement!! I've had 3 attempts at getting decent cart springs and given up! I'm still using the old saggy things. I've still got the lever arms on the front, but I spent a long time getting a decent compression and rebound rate AND getting them to match! I also use synthetic motorcycle fork oil, which doesn't suffer the same performance variations when cold/warm/hot.
Allan Reeling

I had two sets of Parabolics (possible three - read on!!). The first set from MGOC, looked ok to start with, but did not match as a pair, I tried them on the car and they sat very uneven, and when fitting them you could tell that they where different spring rates, so they went back. Second set came fro Jones Springs in the midlands, very helpful, but the springs took about 6 weeks to arrive, when they did they looked great, good quality, well made......however, when fitted they car sat 2” too high at the rear. I checked the spring rate (force/deflection) and it was nearly 1.5 times too high. Jones springs said that their rolling machine could not go any lower, but they would try an alternative. The alternative turned out to be some very poor quality springs, I suspect that they came from the club or Moss.

Anyway, cut a very long story short about the spring makers in india, the price and design (I actually managed to get some original drawings for the springs from BMH on the strict instruction (and promise, not to distribute), I decided to make my own, quite easy in the end, the tempering was done by a firm in Manchester, total cost is about £400 so far, not accounting for my time !! I'll upload some spring pictures and info too if anyone is interested.

No idea why the dampers are mounted at an angle, from an engineering point of view, they should be mounted to follow the arc of the travel, the damping reduces with the cos of the angle, no reason why you would want that!! mine are also inclined fractionally inward to follow the arc of travel and add stability to the location. it also puts a sideways force on the shaft and seal causing them to fail, the seals are not designed to take a load, that is why most people end up going back to reliable lever arms.
MGMike1

A pal is on his second set of parabolics from MGOC, the second with no guarantee, as they say he is using too much power and winding them up. But at the same time they were too high as well! It seems an awful lot of time, trouble and expense to go to.
PaulH Solihull

And the second set are showing signs of distortion after 2000 miles, with one side now slightly lower than the other.....(Same side as before-nearside/UK passenger side

One option is to have an extra "short" leaf mounted under the lower leaf that "should have no effect under normal use but will prevent wind up". A forge known to the UK V8 register says it can repair, re-temper and fit the extra leaf. At the moment I am living with it and will see what its like late autumn. I know nothing about springs so any comments welcome! I just want a more comfortable ride than with cart springs. I have Koni Classic tube shocks.
Michael Beswick

I had 2 sets of springs from Jones Springs, both settled on to the bump stops within 5 miles. They went back. So still looking!! As for the spax top mountings, I think i'll make some brackets up to re-orientate the "tubes". Is vertical the way to go?
Allan Reeling

Many motorcycles with swinging-arm rear suspension had (external) damper/spring units at an angle, and in the case of Velocette that angle was variable to adjust the damper/spring rate. That's not to say it was ideal.

If you make your dampers vertical I would have thought that you will harden the damping slightly, and many telescopic dampers are reckoned to be usable only on the softest settings.

Hopefully not tempting providence, but I've got parabolics and Gaz on mine, and after 4000kms I'm still happy with the set-up...

I suppose you could always ask Spax why they're not fitted vertically?
John Bilham

Isn't it sad that, after in excess of 100 years of producing leaf springs in this country, we can't get decent replacements. Even more surprising that the Owners Club, who you would think would have a vested interest, and have the buying power, would make an effort to find a reliable source of coils, carts and parabolics. Not to mention commissioning properly rated and matched telescopics. Nothing like a good moan!!
Allan Reeling

This thread was discussed between 11/08/2011 and 27/08/2011

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