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MG MGB Technical - Rear Suspension Question

I'm working on my 1980 LE and encountered a question for the MGB gurus here. It has new leaf springs and once I dropped it off the jack stands, it rides high in the rear. I got the Moss lowering kit and am installing today, but ran into a question. Once the lowering "block" is in place, its "male" part strikes the "female" part of the axle slighlty forward (toward front of vehicle). It's likely that I can remove the axle straps and all will meet up, but I have a suspension geometry question. The 80 LEs have the rear anti-sway bar attached to the axle. That means that the axle essentially is restricted to an arc (moving closer to the front of the vehicle when the rear rides up and further when it "bottoms") instead of a vertical up and down movement. I hope this makes sense. Thus, when adding the lowering blocks between the leaves and axle, I'm at a different point in the anti-roll suspension arc and should increase the length of the anti-sway bar accordingly (adjusts just like tie rod ends). It's been 45 years since I took Analytical Geometry and Calculus. Does anyone know how MGB fitted the suspension with the anti-sway bars? What was the "default" position of the suspension when fitted? Were the car's leaves compressed to normal resting position and the anti-sway bars adjusted accordingly or were the leaves extended (car raised by points on the body)? The point being that for least resistance to the drive train, the driveshaft should be in perfect alignment with the rear of the transmission reducing resistance caused by U-Joint flexing. If I don't adjust correctly, I increase the U-Joint flex as well as over restricting the upward "bounce" of the car while reducing the car's "bottoming" restrictions. I hope this makes sense to someone.
Rick Penland

What actual height are you trying to achieve at the rear? Is it lower than stock? In which case I would say lose the rear ARB altogether.

If you are fitting the lowering blocks to compensate for too high rear springs then I am not sure. But you shouldn't need to do that. There is quite a bit in the archive about rear springs being too high. I saw that myself with new springs so when I lowered my 78B I had the original springs rearched to be lower and fitted lower and stiffer springs at the front to drop the height of the car all around. The rear bump stops were cut down to make sure I still had enough travel. I fitted telescopics at the rear and they work well but I think that's because I also increased the stiffness at the front at the same time.

I fitted a uprated front ARB and removed the rear one completely. Car handles nicely although to be honest I don't push it much.

Simon
Simon Jansen

The 80 LE was level (front to rear comparison) prior to the new leaf springs. The old ones were in awful condition and I found them on sale a while back and replaced them. All I'm trying to do is get the front (no modifications except performance bushings) and rear level with one another. I'm reluctant to pull the rear sway bars and can likely figure it out, but curious if someone knew how British Motors set them up. I suspect the adjustment is made with the car "at rest" which means I'll have it on the jackstands with jacks under the leafs to the point that I see the car begin to come up on the jackstands and then adjust the anti-sway bars so the mating point on the axle drops right into place. At present, it's not aligned correctly, but was fine until I added the lift blocks.
Rick Penland

Rick-
Rather than using blocks, just get a set of rear leaf spring hanger assemblies for a Chrome Bumper model from British Motor Heritage Ltd over in the UK. Cut off the old ones and then weld the new ones on. That will lower the rear of the car. They're part# BMH9002 (right side) and BMH9003 (left side), 24.63 UKP each. Click on this: http://www.bmh-ltd.com/p61r.asp
Stephen Strange

I over complicated this one. I'm sure you can spend a while determining angles and side dimensions of a scalene triangle based on the measurements I could determine and come up with an exact length, but I don't have all the specs needed, so I just "eyeballed" and measured some things. My conclusion was to rotate each end of the anti-sway bar ends 6 full turns shorter. Thus, I reduced the length of the anti-sway bar ends about 3/8ths of an inch. All falls in place perfectly, the rear differential is pointed directly in line with the rear of the transmission (as I can best tell), one side is bolted up and I'm doing the other side. Cars without the anti-sway bar won't encounter this when adding the lowering blocks. It's not very mathematical or scientific, but hope it helps someone. The end result will not be a car lowered to chrome bumper height (been there, had one and picked up exhaust system from road after speed bump more than once), but a rubber bumper with even height front and rear.
Rick Penland

If the rear rides high with new springs, i.e. the rebound straps are taut or nearly so, then the springs are wrong and this is very common. They should be nearly flat with a fully equipped car, a distinct bow in the rebound strap, and the rear shackles angled backwards.

Surely the 'fixed' end if the anti-roll bar is forward of the axle, so whilst it may move in a slight arc around that point the fore and aft movement is a relatively small amount compared to the up and down movement.

If you really can't get the axle and spring aligned properly to fit the U-bolts, then adjust the front eyes of the anti-roll bar accordingly. I've recently changed springs on one of these and whilst I had to give the drum a kick on the 2nd side it did then just drop into place. The first side is easy, just rotate the axle casing.
PaulH Solihull

Dropped the car down on my shop floor with new leafs and adjusted lowering kits. Measures less than one inch difference between floor and bottom of chrome front to back. Up to half inch is likely difference between rear wheels (tires removed, wheels stripped and new POR 15 Clear Coat applied) and front wheels that tend to not hold air pressure as well as rear does now (next step is same as rear wheels). I'm happy with the solution and about 30 days to go before it goes on E-Bay.
Rick Penland

You should measure between the centre of the axle and the bottom of the chrome strip, as that ignores any differences in wheels, tyres and pressures. An inch front to rear is quite a lot, they should be pretty-much the same.
PaulH Solihull

You are correct about proper measurement. I simply used a tape measure for a quick measurement. The actual difference is just under 3/4ths inch front to rear and I find that quite acceptable. The entire suspension has been upgraded with Energy Suspension's prothane bushings (front and rear) and I'll loosen and retorque the shackles on the rear now that the car is off the stands which may adjust a fraction of an inch or so. All in all, it's a significant improvement to the car, but I haven't driven it yet. The engine needs to come out next to replace the front transmission seal before firing up. After replacing, cleaning and repainting almost everything under the car, I don't want to ruin all that work with more leaking oil.
Rick Penland

This thread was discussed between 24/08/2010 and 27/08/2010

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