Car pulling to the left very badly? Diff?

[Wildfire]

I've just driven my brother's car, which is pulling very badly to the left and has been doing for a while now. But we have had all the geometry checked on the front. The car pulls very badly, but is particularly bad when you let off the throttle, where you get a sharp yank to the left. The gearbox was rebuilt recently, but at the same time the geo was out.

Could this be an incorrectly shimmed diff?

All the tracking etc. are spot on?

Could it have something to do with the rear geo?

[baller11]

could be worn steering rack....that was the problem with mine.
or track rod ends worn.

To check the rack,undo the track rod end nut, pop the joint and the steering arm should be pretty stiff to move and hold in whatever position you leave it. If it flops about then its ****ed.

Dave

[phumy]

The OP already stated that he had had a Geo check, that would have picked up any track rod end deficiency/failings.

I would look at subframe mounting points, does the car appear to "crab" when driving? this would give an indication that something is not all square.

[Cooperman]

The rear geometry is particulary critical for optimum Mini handling and steering. However, with a sharp pull to the left it seems unlikely to be that, although it's worth checking. Get someone to drive behind the car in a straight line and see if it is 'crabbing'. Remember, though, the rear th=rack is 2" narrower than the front, so you have to look to see if both sides are the same. We did a Mayfair recently and it was about 3/4" out front to back. You can check and correct this with a long straight piece of wood, a square board of plywood about 18" square, a ruler and some thin steel sheet (email me privately for more info on this).
I do seem to remember this pulling/snatching problem following a gearbox/diff re-build many years ago and it turned out, if I remember correctly, to be an over-tight diff output shaft bush which had not been honed out sufficiently. The problem cleared itself after about 200 miles. That must be a rare occurance, but these things do happen sometimes. Try jacking both front wheels up and running the car in gear to see if both front wheels turn freely together. Switch it of and with the car in 2nd gear, hold each wheel in turn and turn the other one - in fact you could do this first. Is the same effort needed to turn each side? That might just give you more of a clue to the problem.
I hope all this helps,
Peter