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MG MGB Technical - Rear Axle Location

I recently discovered on my 68 MGB-GT I had purchased, that the lateral location of the rear axle is offset to one side by about 1/2". This became evident when I replaced ther rear tires and noticed that one was closer to the inner fender edge than the other.

Is this a simple fix by lossening the U-bolts and just sliding the axle over the requisite amount ? Or is there a location pin that determines the axle location on top of the spring assembly ?

My service manual is unclear on this detail.
Colin stafford

Colin, there is a locator pin on each spring, but you also have a rubber spring pad which surrounds these pins and could be worn. It's not unusual for most B's to have the axle offset a bit, midgets also. Don't know why. There was a thread a few days ago about finding springs which were not straight and caused some offset. Check the archives, this subject has come up before.
Bill Young

Colin,

If you measure the location of the wheels relative to each other you may find that the 4 wheel are correctly placed and that it is the bodywork that is not straight!

Most people just accept it.

David
David Witham

I will get out my laser level and check the alignment,
It does not seem to effect the cars handling.
In the past I have seen people get axles back in the wrong position (longtitude direction) in T Cars.

Colin Stafford

"In the past I have seen people get axles back in the wrong position (longtitude direction) in T Cars."

Colin--you mean with the drain plug on top!! lol


Paul Hanley

Colin, the offset of the bodywork is frequently mentioned in the archives. In fact, I believe it has even been documented in the heritage shells.
Regards,
Dennis
D F Sexton

Yep,

I bought a Heritage shell, and the axle position was offset.

It's not too difficult to centre if you need to (wider wheels in my case) but sideways location is a problem, as the axle can move considerably, harder bushes and spring pads help somewhat, but to fix the position requires a Panhard rod.


Mike
Michael barnfather

Mine is offset to the left by approximately the same amount. Stayed this way forever, including after a rear spring replacement.

Since this offset is so prevalent in MGB's and even occurs in Midgets, there must be a reason for it, although no one has been able to decipher a reason for it. If it has been documented in the Heritage shells, obviously the factory intended it to be this way. I just can't see a carmaker making a car for years on end having the same mistake in it. It must be for some purpose. There may some engineering considerations that none of us have though about. It may even be something as obscure as a torque issue - maybe the offset compensates for a natural tendency for the axle to offset the opposite way on acceleration (note that the springs are the only locator for the axle and springs flex and twist). A full analysis of the forces involved might provide an answer. Just a thought...
Richard Smith

Good point Richard. I think the other thread about "IRS" says exactly that. Just off to check....
j w mcglynn

Here you go,

"Engine Torque: Engine rotates the driveshaft counterclockwise (viewed from the rear). That rotating force is transferred to the axle. As a result, the axle also tries to rotate counterclockwise and weight is transferred from the right rear wheel to the left rear wheel.

Therefore, if all other conditions are equal, there will be more weight transfer at the rear wheels in right turns because the weight transfer from engine torque is added to the weight transfer from cornering forces. This increases the tendency for the car to oversteer in right turns. There is relatively less weight transfer at the rear in left turns, because the weight transfer from engine torque tries to rotate the axle in the opposite direction of the weight transfer from cornering forces. "

Not sure if that is the reason or not. Got to try and absorb that now and have a think !
j w mcglynn

One of the most oft discussed topics relating to an MGB, along wih whether to use the spacer tube and shims in the front wheel bearings (yes)! They are pretty-well all like it, and most with the left closer. Mine is the same after replacement axle and springs (for other reasons, and a four-wheel alignment shows the rears tracking the fronts. If you get the wheels equidistant in the arches you will be crabbing.
Paul Hunt

This weekend we had a MG get together and I checked 7 MG-B's and found that all of them had the rear axle offset by about 1/2" to 3/4".....much to the suprise of several owners.
Colin Stafford

JW,

Had to let what you wrote about engine torque sink in a bit. With the increased weight transfer to the left wheel during right turns, it stands to reason that the left rear wheel will have more traction while turning to the right. The increased tracion might cause a tendency for the axle to shift to the right during a right turn due to the increased reaction provided by the left wheel. Does this make sense? Since the opposite is true on a left turn the DECREASED right wheel traction has less chance of offsetting the axle to the left. Using this logic a permanent slight offset to the left seems logical. Am I missing something here?
Richard Smith

Colin, I had the same problem -- only with new leaf springs. Turns out they were not straight which caused the axle to be offset toward the LH side about 1/2 inch or so. Assuming that the springs are correctly mounted, you won't be able to shift the axle back because it is fixed in position by the springs.


Tom
Tom Custer

On my '67 gt I've gone to a '75 disc wheel rear axle assembly. I'm using fiberglass springs, with 6" x 15" alloy wheels - 195 55 15 tires. The fender edges are stock and not rolled under. I am planning to- but have not gotten around to it yet -- install a panhard rod. In the meantime I have found that a 1/4" wheel spacer on the left side and no wheel spacer on the right results in almost no fender rubbing at all even under extreme conditions. This would suggest to me that my axle is offset to the right side.
The car has not been damaged and any bias would seem to be from the manufacturer.
Barry
Barry Parkinson

I cannot comment on whether the MGB body is straight or not with regard to the rear spring hangers, but what I can say without question is that most of the problems are caused by poor quality springs. I have just had a conversation with the sales manager of a
spring maker in UK and he admitted that they could not guarantee any better than 10mm side twist in their springs. I have looked at and measured several springs and every one was twisted the same way, throwing the body to the left, the best I could find had 7mm deflection at the centre. Obviously this is a problem inherent in the production procedure and since it appears to be in one direction, you would think it could easily be corrected, but no because, "we are a mass producer of springs and thats what you get, if you want straight springs, go to a small specialist maker."
This attitude seems rife within the spares market and until we start returning unsatisfactory goods, it will remain.
The company has the unfortunate name of BRITISH SPRINGS, their website is www.british-springs.co.uk and on their home page they state "Our focus is on quality from start to finish" The problem is they obviously don't know what quality is.
This company supplies springs to Moss and MGOC amongst others, so when you buy them look carefully and if they look bad don't accept them.
An easy check is to stand them up side by side, when the gap between them should be equal in the middle and at the ends, then turn one around so that the eye end is opposite the shackle end and the gap in the middle should still equal the ends. If it is wider they are bent.
Publish what you find, and lets get better quality.
Graham
Graham Cherry

Graham, that's interesting! And it's what I suspected. I purshased springs from BritTek and Moss and they both looked the same, like they were made by the same manufacturer. And they both had similar amounts of side twist -- enough to shift the rear axle and cause the RH tire to rub the inner body.

I returned the Moss springs yesterday. Still need to return the BritTek springs.

Thanks for your post,
Tom
Tom Custer

Forgot to ask a question!! I wonder if the side twist can be removed by a spring specialist!

Thanks,
Tom
Tom Custer

Tom, yes I believe it can, but you'de be looking at around $100 extra on a new set of springs. You may actually be better off having your old springs rebuilt and specify that side twist is a problem with these. In the long run, a rebuild will be cheaper, and you can have them set the ride height where you want it.
Jeff Schlemmer

My own opinion on this, especially from reading about how the Heritage shells are put together from the original Pressed Steel dies and still require large amounts of body work, is that Pressed Steel or MG screwed up the set-up jig from day one of production and never went back to fix it. It does not seem reasonable that MG discovered some hidden mantra about weight transfer axle offset that would only apply to the MGB and none of their other cars, nor any other car manufacturer in the world for that matter. Both the Magnette and MGB were semi-monocoque/monocoque construction and I have not heard of the offset problem with the Magnette.

When you think about the stock tire being a 145 mm width, the offset would never have been considered a problem. I run a panhard rod, quarter inch spacers on both rear wheels, and rolled lips on the fenders in order to fit the 195/16 x 15 tires in my '66 B. Without this, there would have been constant rubbing on the left hand tire and it would have been cut through in a matter of a couple of hundred miles. I guess the bigger issue is that we are now running maximum width tires and exposing a fault that has always existed.
Ron Kluwe

This thread was discussed between 18/05/2005 and 30/05/2005

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