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MG MGB Technical - Rear Axle Offset problem

I have just noticed that one of my rear tyres is hitting the inner wing.
If I measure between the tyre and arch I get about 1/2" one side and at least 1 1/2" the other. The axle is not sitting in the centre of the car.
I have fitted new springs some time ago and have also fitted Spax Shocks instead of the lever arm units. I have also lowered the axle 1".
I believe the rear axle is only located on the springs.
What can I do please?
Would one solution would be to swap the springs over to hopefully get the axle better centered.
I am not happy with the new shocks so I might replace the leverarms which I believe help sideways location on the axle.
Any help would be appreciated.
Dave
D M Tetlow

Dave. you need to search the archives. This problem has been discussed at great length in the past. Changing the springs and shockabsorbers from side to side will NOT alter the position of the axle relative to the body. Some say that they have found the position of the spring mount plates welded to the axle incorrectly though I have never seen one of those. It always seems to be errors in body assembly. Unless of course someone knows differently. Jim
j soutar

Thanks Jim
D M Tetlow

Check your springs with a straight edge, they may indeed have been made to compensate for the common half inch offset found on MGB's. I have heard of this being done. Try loosening the u bolts and retightening while applying a load in the direction you want. Check that the front hangers are straight, they may have got a knock at some time.
Here's a thought, that some one might like to commercialize-
You have one inch blocks currently. It would not be too hard to make up a set with an off set in them.
Go buy a chunck of aluminium from ALCAN, or some one like, It should not be hard to make up a set that can locate securely and be bolted down hard. I would imagine that one of the U bolts would pass though two holes in the wider block, and it would need a small step if it goes over the edge of the perch on the other side. I can't see that coming adrift at all.
Peter

Despite the offset which seems universal (closer on the left, although some claim to have it on the right) it *shouldn't* be a problem if you have the correct wheels on the correct axle, and that goes for lever-arms or tubulars. Wire wheels on a steel wheel axle will almost certainly have problems, after-market wheels with the wrong offset can have, and very wide wheels can rub on *both* sides of the tyre. Personally I haven't found tubulars result in any better axle location, although a rear anti-roll bar does.

And remember that as long as the chassis and springs are straight, doing *anything* that moves thw axle across the car will result in the car 'crabbing'. As Jim says, the offset mainly seems to be something to do with the original body panels and jigs.
Paul Hunt 2

I have measured several axles, and found the mounting pads offset by varying amounts on every one. If your carful to make sure the axle is as far to the right sid as poss. while tightening the u bolts, you can make a slight improvement. Don't expect to gain much, because there is not much movement to take advantage of. BTW how do you change your e-mail in here. I've change it in my profile, but it won't change on my posts.
Robin Meier

What offset did you measure, Robin? I've checked mine but they are all less than 1/4", but the offset at tyre and arch is several times that.
Paul Hunt 2

Can anyone at Heritage shed any light on this? A lot of their jigs are (or at least were) original.....

Dave.
Dave Smith

I am struggling with the same problem. My left rear wheel wants to rub against the fender, my right wheel has at least 1.5 inches gap. I raised my car, and hung a plumb bob from various points under the car eg front and rear spring hanger eyes, inner lower A-arm bolts etc. I tried to make sure I was hanging the plumb bob from comparable points on each side of the car to make the measurements as accurate as possible, and marked the locations on the garage floor (my wife wasn't crazy about this...!) Then I took a string, tied a loop at the end, and using a marker in the loop and holding the string on each point marked on the floor, I made arcs on the floor, and found the intersecting points of arcs made from each direction. Then drawing a line down all the arc intersections, I found that they all lined up very well. The missallignment was too small to explain the difference in the location of the axles.
You can also measure diagonally between all the points to see if everything is square.
Then I used a small ruler and measured the difference in locations of the spring mount plates on the axle, and it was 1/4 inch different, but in the direction that actually helps my gap problem!
My conclusion is that the left fender does not bow out as far as that of the right. This may be from a bad fender repair job - there is evidence of body damage on that side of the car.

HTH, Erick
Erick Vesterback

Dave,

the things Paus is refering to must be checked out. Wrong tyre size and too large rims with wrong offset are often offered nowerdays and anything more than 5,5 rims and 175 section tyres do not help to give dramatic improvements although thy are more eye catching than the standard sizes.

The wheel arches can be flared for having a further 1/2" of room, otherwise a torsion bar kit from the MGOC will help to keep the axle in position.

A change of the springs from one side to thge other normally does not show any changes and the shocks do not help to keep the axle into position.

If the front bushings of the springs are O.K. and the rear shackeles are straight and their bushes are not worn out, considre upon tyre and rin size and if there is nothing wrong with it, i would try a panhard rod kit.

Keep us posted, please.

Ralph
Ralph

Re Heritage - I wish I had thought of that a couple of weeks ago, I was at a run talking to someone with a recent reshell, I could have done a quick measurement. It's the New Forest run this weekend (lousy weather forecast) but I doubt I'll be lucky enough to come across another.

Erick's careful work does seem to prove the point that if you move the axle so the tyres sit central in the arches, you will cause the car to crab. Looking at my roadster the left wing seems to bow out *more* than the right (both half-wings replaced at some point), but that is still the side with least clearance, meaning bthat whatever *is* out, is out *more* than the tyre clearance would suggest.
Paul Hunt 2

I have been reading the threads on this problem for a long time now and I have done many things to reduce the problem on my V8 conversion which has standard diff housing, 15 x 195 x 60 tyres on centrelock minilite replicas.

I have knocked the lip up a little and ground some of it away. I do not wish to change the appearance of the car by flaring the rear guards. I have also fitted the shorter splined hubs designed for use with a disc wheel axle housing and wire wheels.

I am sure this has all helped but the problem persists especially with 2 up and some spirited driving.

I am tempted to shorten the diff housing on the left side by about 10mm. I would need to remove the housing and have the job done by a differential specialist.

I am hoping that the drive axle shaft will not need to be modified, ie it will move 10mm further into the planetary gears and I will only need to shorten the housing.

It is a lot of work for a small gain, but now I have done so many other things I think it would be worth it on a life car. (40 years so far)

What do you think?
Ian Buckley

It is funny i think, this problem is never discussed for racing cars but comes up for normal road going B's every season.
Just think about the original tyre size Abingdon 'felt' to be adequate for the B and you might considre to a change from 155/165 SR 14 to 175/70-14.

O.K, these size does not look that sporty than a 195/60-15 size, but it is more in tune with the geometry of the axles (front and rear) than 'more modern' dimensions are.

If you want to keep these wide tries, take a WW axle and modyfy it for four stud rims. Narrow spacers for Nissan or Honda cars (5 mm) used in conjunction with rims from the Reliant scimitar GTE will give you enough clearance and restore the basic dimension good enough to cure the problems even with 185/70 on a power slide with the V8.
After trying 185/70 tyres i am back on 175 size ones and there is no dramatic difference for roadgoing cars, not with the roadster and 118 RWHP, nore with the V8 with 183 RWHP, although more than 130 MpH is no fun anymore.

Ralph

Ralph

Dave, some of the new springs are not straight and will produce an offset. Find an original set (must be straight!) and have them rebuilt at a spring shop.

Tom
Tom Custer

Paul, I measured from spring mount to backing plate on each side. I got my axle centered to within less than 1/8 inch of offset(can't remember exact amount). I run 205-50-15 on 15x6 rims for autocrossing, and need to use a 1/8 inch spacer on the right side to keep from rubbing the inner wheelwell. More careful measurements I think would show a combination of things offsetting the axles, not just the mounting pads, because my tires are more offset than the axle measurements would suggest.
Robin Meier


Move the spring perches, if it's a problem.
Or jack out the guards. Car jack, piece of wood to spread the load. Easy to do and you will not notice 5mm.
Peter

Moving the spring perches *isn't* the cure, that just causes the car to crab, by destroying the alignment of the front and rear wheels.
Paul Hunt 2

Paul - I agree with you that in many cases the rear axle is in good alignment with the front wheels and the underbody of the car, and its likely the fenders that are out. Moving the axle to one side to solve the clearance problem would missallign the rear wheels relative to the front, causing the crabbing. My question is, how much does moving the axle to one side by .75 inches affect the handling of the car - would it be significant? Would the improvment in handling of the car with wider wheels/better tires not be significantly greater than the loss in performance caused by the small misallignment? I have seen lots of cars over the years - various makes - that look like they are crabbing by 3-4 inches as I drive behind them.
It seems to me that rectifiying the body situation with fender repairs could be alot tougher to do.
Erick Vesterback

Hi Guys
I understand this is an inbuilt problem, some MGBs the axle is longer on the near side or offset making it longer, if you have the normal crap springs the body is low, this is why the arch rubs on the tyre.
My 72 GT was the worse, I fitted Avon 338 tyres they only do them in 185, I fitted them to the fron with no problem, when fitted to the back the arch was rubbing te digets off the tyre wall, I fitted spring helpers obtained from the states, this cured it, it lifted the rear of the car some 2 inches.
Hope this may help.

Colin
Colin Lanning

Hi Colin
Thanks but I need to do the opposite. I have a Rubber Bumper body with chrome mods, that was too high so I have beeen trying to lower the car as much as possible!!!
I have 15" 185 MGC wires which also flex when under load.
Regards
Dave
D M Tetlow

Mine rubs the right tire, also more with 2 up and when being a lunatic. I tried grinding the inner lip and turning a baseball bat along the tire front to back to ease out the arch (an old Porsche 356 trick). No improvement.

Gently, or thrashingly if you like push/pull the rear of the car sideways (or get someone else to as you play spotter from below) and you'll likely see much motion, probably from the rubber shackle bushings and the puny springs themselves. The cure as I see it is urethane bushings and a panhard rod.

Art Dodge

Gents,

As so many before me, many have been at the same point before. Talking to the technical support group of the MG Owners they said that an offset of 1 inch was the maximum during the original production. At this point I mean the offset of the spring attachment points underneath the body.
This would be compensated during assembly by installing a rear axle having the offset the otherway round.
During the rebuild of my car with a heritage body I came across this point.
I removed the axle mounting points by grinding and installed newly made supports by welding.
If anyone is interested I can submit both drawings of one of you who did the same excercise before I did.

If you really start measuring there is hardly a thing symetric on a B. We are in good company, however, just check the dooropening on a early Aston-Martin of Ferrari. Differences in excess of an inch are easily found. It is a car from period where these
matters were considered differently.
Have fun in life.

Kind regards

Frank
Navest

I had my 2003 BMW loaded with 750Kg of sand yesterday and as the wheels had nearly disappeared into the arches I thought why not check the clearances.
One tyre is at least 10mm closer to the wheel arch than the other.
I assume that even today geometry’s of the wings cause differences.
I am going to centre mine as best I can with clearance in brackets etc, and get the wheel alignment checked. If the man from Tyre Fit says YES then I will leave all alone.
Dave
D M Tetlow

This thread was discussed between 27/05/2007 and 15/06/2007

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