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MG MGB Technical - Suspension upgrade

I'm planning to revamp my MGB (78 rubber bumper) suspension. Current plan is to lower it, go with rear Spax conversion and replace all bushes front and rear with poly bushes.

What else would anyone advise? What's the best way to lower the rear - new springs or lowering blocks? Are Spax the best rear conversion?

For background, the car is currently stock performance spec and I don't really have any plans to change that.

Thanks, JH
JeffH

Hi Jeff,
I lowered mine a few years back.
I had read that new springs are of a low quality so I wanted to keep the orrigionals which were in perfect condition. I also wanted to keep the softer springs because the word on roadholding is to make the front as stiff as possible and leave the back soft so as to allow the live axle to follow the road surface and keep the max' amount of rubber on the road. Some people even take leaves out of their springs to soften them up. The lowered springs availiable then were all of the uprated stiffer variety.
On the front- Lowered uprated, stiffer front springs and a 7/8 ths antisway bar. Bigger the better. No antisway bar on the back.
On the back I began by redrilling the front hanger (of the rear springs) moved the hole up as far as it would go, back to the chrome bumper location. It is quite easy to do this so long as you use a centre punch, drill small pilot holes and use new sharp drill bits. Other wise you might easily go off centre and make a mess of it. Took me about an hour to do including removing and replacing the wheels, so a quick job. This was not enough, I also had removed that big heavy rubber bumper (around 25kg!)which raised the car up a bit further. So I then fitted one inch blocks. This got the ride height at chrome bumper, level with the front. I did not just use two inch blocks to begin with because I'm running a V8 engine and two inches struck me as too much leverage on the spring. This approach also ment that I did not have to change the shocker links for chrome bumper ones, which you will have to do it you use flatter springs.

I've kept the armstrong shockers. I can always put a heaver weight oil in them (ie 30weight) if I feel the need. I also have read lots in the archives about how spax are way way too hard, even on the softest setting. A few people say they like them though.
Also there is less unsprung weight with the armstrongs. Less $$ involved as well! Armstrongs are also suprisingly well designed. They have two sets of valving in them so good condition armstrongs are superior in action to the majority of shockers. A negative is that I've read that some rebuilders of armstrongs often don't do a good job. As turned out to be the case with one of my front ones.

I've used the poly bushes. The blue, or standard road use grade. These are very good. When I bought the car they had just fitted new rubber bushes in the front, so I have a good basis for comparison. The poly bushes are firmer, keep everything centred better, but are less harsh than the rubber. Less crash and rattle going on. I belive it is because of the way these fit, the two halves of the bush are squeezed together (over a stainless centre tube) as you tighten the nut. The result is a very tight tensioned fit. Do use the special grease provided,lavishly, otherwise they will sometimes make squeeky noises and you will have to pull them apart and regrease, as I did with one. There are two harder grades of poly bushes availiable (race track use) but the only comment I've heard about these was negative. So hard that one person took them out again. However, I do have the harder "yellow" grade bush on my front antiswaybar, which is what it came with. Seems OK there.
I also put in new poly bushes between the crossmember and body but could detect no real difference for those, so if you don't have to don't bother with those.
One thing you must do, is reduce the height of the bump stops. As they are with chrome bumper ride height, you will have about 1.5 inches of suspension travel. Not enought. This is not just a comfort issue. I found that about halfway through a corner a great deal of oversteer would suddenly appear. The outside bumpstop was contacting and then levering throught the outside wheel to lift the inside wheel a little. At least that is what I think was going on. I simply cut about one inch off the rubber bump stops with a hand saw, and the problem went away. Another approach is to remove those grafted on cresents of metal and relocate the bump stop base back back up into the chrome bumper spot. It should be quite easy to do because the chrome bumper metal surface is still in place under the rubber bumper add on. You would need to either spot weld or perhaps just rivet the bumpstop "mushroom" base to the newly exposed surface so you have something to attach the bump stop to.
Peter

You will find a lot of information on shock conversions in the archives, but the general concensous is that the levers are as good if not better than tube shocks on MGBs. If you need the adjustability, you can order adjustable lever shocks from Peter Caldwell. Then you won't have to modify the car, and your shocks will last another 30 years.
Steve Simmons

As others mentioned before me, stay away from the telescopic shocks (Spax, Koni, ...) as all they seem to do is make the ride harsh, even on the softest setting!
The best handling mod on my car is definitely the 3/4" front anti roll bar.
Alexander M

And even when the adjustable Spax *have* softened up, over the next 70k or so, you will find the adjusters have seized. And even when you free them up you will find it makes precious little difference anymore.

The only time you need to depart from the standard lever-arms is if replacing the multi-leaf springs with single leaf or parabolic, which *do* need more damping as there is significant damping in the standard multi-leaf springs.
Paul Hunt 2

Very interesting indeed on the Spax front - just assumed (from my dealings with midgets) that they were a good way to go on the B.

What about thoughts on lowering blocks vs. new lowered springs on the rear? Is there a significant difference?
JeffH

Lowered springs is probably more rigid. Whichever, you will need CB axle straps, bump rubbers and lever arm drop-links to keep damper travel correct.
Paul Hunt 2

I think that it's likely that the blocks will lower the roll centre a little, a little like moving a panhard rod further down. This is a good thing insofar as grip at the rear goes.
I've no proof and I haven't heard this mentioned before so I say it expecting to be corrected. What do people think?

By the way I do intend fitting a panhard rod fairly soon (as well as three trailing arms and coil springs)
Peter

http://www.fastcarsinc.com for the front suspension,

http://www.advanceautowire.com/3-link for the rear (from Fast cars as well)

These two items are about as good as you'll get.
Dan Masters

Don't blocks and lowered springs have the same effect as far as the roll centre goes? If they both end up with the same ride height? Unless you mean that with blocks the weight of the springs is lower, which has got to be pretty marginal short of F1 territory :o)
Paul Hunt 2

Peter

The front and rear of the car can't roll independently of each other and contrary to what many textbooks either state or imply, a car does not roll around its roll centres or roll axis.

Roll axis inclination affects the “feel” of car during transients. A roll centre is not a centre of motion, but can be considerd as a force centre. It determines what proportion of suspension forces are transmitted via a "fast" mechanical route and what proportion are transmitted by a "slow" suspension spring/anti-roll bar/damper route.

A high roll force centre gives more load via the "fast" route and less via the "slow" route. Thus for a typical vehicle with higher rear roll force centre than front, the rear tyres load up faster during turn-in which is usually considered beneficial. Adjusting roll centres are therefore a handling tuning tool.
Paul Wiley

Does anyone have any pics of what a rubber bumper B lower to chrome bumper level looks like? I've just seem a very low RB model on the road and it didn't look good! I just want to make sure that I really do want to lower :-)
JeffH

I have Ted Lathrups Fast Cars set-up on the front of my 1979 MGB and John Hoyle's IRS on the rear with the car set to chrome bumper ride height and I think it looks great with my rubber bumpers (Mine is a MGB LE so the car is all black)!
Frank

This thread was discussed between 16/10/2006 and 19/10/2006

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