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MG MGB GT V8 Factory Originals Technical - Centering the rear axle

I see that the thread "speaking of wheels" has developed into an exchange about centred axles. I'd lke to know more and felt it would be worth having a dedicated thread. I've just returned from visiting Paul who kindly let me try his 195/15 spare wheel on my V8 - thanks Paul. I can see that my SD1 axle would have to be centred to be able to use that size tyre.
Why are B axles off centre in the first place?
If you centre the axle, which I can see is a fairly simple job involving moving the axle pedestal and strap brackets, what happens to the propshaft/differential alignment.
Anyone in the UK who can do this job?
Any other info?

I have a factory V8 and with the original springs my axle was about 10mm to one side. I carefully took measurements and moved the spring mountings by welding plates onto the originals. I ordered a pair of composite springs and installed the axle.
Expecting the axle to be slap bang in the centre I was surprised to find it was way out. In the end I removed my modification and the original location was perfectly central. ( all that work for nothing ).
I cant explain why the composite springs centered things up.

Worth a try but expensive.

Mark Rawlins

Since the brackets on the axle are symetrical about the true centre of the axle (i.e. they are equidistant from the ends) then any misalignment must be down either to incorrect body dimensions ( unlikely unless badly repaired) or the springs being out of shape or the bushes/hangers being off centre.

It does not surprise me that the composite springs have centred the set up - they must be stiffer laterally than all those layers of steel!

Also I suspect you replaced the bushes - I found that poly bushes helped tremendously.
Chris Betson

I haven't checked the rear axle centering on a lot of B's, but every midget I have seen has the rear axle visibly off center. I suspect that the factory didn't use very accurate jigs when welding up the tub.
Bill Young

This was a concern for me also. I took a carefull look and without pulling out the calipers etc, the HUBS are set equally inside each wheel well. The DIFFERENTIAL itself is skewed to one side, but the hubs are centered in the wells equally..
Larry Embrey


Good to see you, exchange visits can be thought provoking, hope you had a good lunch.

As the SD1 axle is a cut and shut job it may be worth measuring dimensions of axle to check diff is in fact in centre of axle. Also worthwhile to get B axle dimensions. Would be useful to have access to blueprints. If it is in centre what are the factory tolerances for Prop to gearbox bearing in mind SD1 arrangement.

My email is playing up but will get back to you on your other points.

Paul Wiley

Seems to be very common on B's at least to have the axle offset to one side. On both mine (roadster and V8) it is about 1/2" to the left. When you consider how many panels there are between the spring hanger and the lip of the wing and the relative crudity of panel location in those days - and particularly after restoration - I can't say I'm all that surprised. There is a significant difference in certain dimensions even in pukka front wings between left and right, can't see any reason why rears should not also have differences. The relative lateral stiffness between steel and composite springs should not be an issue if measurements are made while stationary (is there any other way?) and on the level, if there was a difference between them then one of them must have had a lateral bow, or the rubber mounts were causing it.

Larry Embrey - did you measure to both inner arch panel i.e. chassis rail and outer panel?

Paul Hunt

Time for a chassis drop test where the main datum points of the car are transposed to the ground. Then using fixed points on the axle to also mark the ground the combination of marks can provide the final answer whether the axle is true to the 'chassis' or whether it is the external body panels that are out. Perhaps even a combination of both since the 'chassis' drop test often shows up misalignements to the frame of the car.

Roger Parker

This thread was discussed between 24/02/2001 and 26/02/2001

MG MGB GT V8 Factory Originals Technical index

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