spinning a differential

[pappentl]

I heard a popping and then a steady tic - tic - tic that changed with speed yesterday. I brought the car back and ran the car with the rear wheels off the ground. Only one side of the open differential spins, the other just sits there. Is this a bad diff? I thought both sides should spin unless one is stuck. If it is a bad diff, how much of a slug will it be if I install a 3.07 LSD? Or how awful woth a 3.91 be?

...tom
81 528i

[Mike W.]

I doubt the diff is your problem, normally both wheels will spin, and I suppose a bearing could be going, but it generally doesn't take much to stop one either. It could be a CV joint or maybe even a wheel bearing, but none of those things including the diff fail very often.

As to how it would be with a different ratio, I don't think the 3.07 would be too bad, except 5th would be useless in town, and performance would be down somewhat all thru the ranges, a 3.91 would have you skipping gears a lot and might get a little buzzy, but I put well over 100K on both a Bav and and E12 with 4 speeds and it wouldn't be nearly that bad. Do remember your speedo will be off with either as it's assuming a 3.45 diff.

[Karl in KS]

As mike said, it doesn't take much to stop one wheel if you're running an open diff--just a little drag on one brake will do it. You can turn each wheel by hand to see if you can hear or feel that click as it turns over.