Remembering why I
dislike working on
AO Silver Member
Join Date: Sep 2001
I’ve never seen a bad diff bearing on a manual box, and that assembly is very similar. If they were bad, you’d be getting some serious ‘grumble’ from it. The issue is far more likely the side gear bearing in the carrier and the shaft into the side gear. The side gear bearing is plain steel on steel and the shaft, although a decent fit into the side gear isn’t all that tight and though there is no relative rotation between shaft and side gear of course, there is wear caused by torque changes which cause it to become more sloppy over time.
Sadly, the only way to find out is to strip it I think, although if the 4HP20 manual has a rolling torque figure for the main diff bearings, you could maybe measure that in-situ with just the driveshafts removed and that might give you a clue.
The last manual box I put new bearings in was only because I’d changed the diff for a Q2 and that had none fitted. The original bearings were perfect. The side gears however, not so much. The play visible on your video is pretty bad though, certainly somewhat worse than I recall from my own Sporto when I had it and was messing around that area. That said, the Sporto was worse than any manual box I’d played with up to that point.
What I’m getting at is this. I’m not saying it can’t be the main bearings, just that it isn’t likely at all, and if you do get in there and find the main bearings are OK, the only fix for the issue is a new diff, so be prepared for that. It’s been a while, but ISTR being somewhat put off by the thought of digging into that auto box. Looked like more than a few special tools needed. The manual box holds no terrors though.
A thought. Remove that driveshaft, then see if you can feel how much movement there is between side gear and diff housing. It’s a big enough chunk of metal that you won’t move the diff by gently moving the side gear up and down and side to side. If the side gear moves, there’s your problem. If it doesn’t, see if you can measure the bore of the side gear and the OD of the shaft stub and see how they compare. If that is good then maybe it is the main diff bearings. I appreciate none of that is easy given the location and layout though.