Quote:
Originally Posted by Henn28
...The car developed a slight but very distinct whine from 30 to 40 mph only. Very much like alternator whine through the stereo but only after a cold start and it would stop when the brakes were tapped (drive side versus coast side of the pinion/ring gear maybe?). I'm pretty convinced that this is from the new diff, and must either be an output bearing(s) or the backlash. The backlash was at the very upper end of what Quaife said was acceptable, but I didn't want to pull the pinion. I suppose it could be the pinion bearings too, ebay donor differentials being what they are. I've read that its tough to put too much pre-load on output bearings, but I suppose it could be coming from there too. At any rate, I'm going to drain it next week and look at the magnetic plug. If it is relatively clean with no chunks, I'm going to close it up and live with it for a while. My 1993 grand Cherokee has had massive backlash issues and bearing whine from the rear diff for 15 years and it still makes it to the X5 rescue scene every time. The good news is that I've got the OE diff than came out of my X5 in my shop so I can break that down at my convenience and learn how to rebuild a pinion, set preload, etc....
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If yours isn't too loud, and only whining on coast, then I wouldn't be too worried. I've had 3 whining differentials on my old Chevelle drag racing car, caused by setting them up where the "drive side" pattern was perfect, the "coast side" not so much. But, my diffs weren't the new-fangled Quaife, so I might be comparing apples to oranges.
The first one (a 3.73 Richmond gearset, with Eaton LSD, to be used on the car while it was still street/strip capable) was set up that way by a professional shop, that dealt only in drag-race diffs and axles. They said that the sound (when coasting) was normal for their diffs. I learned to like it, and that diff was still working fine (in another car, after I sold the whole rear end) 20 years later.
The second differential was set up by me and my master mechanic friend, at his home shop. It was a 4.56 set, again with an Eaton posi. Also, again, the diff whined on coast, but the Eaton was too weak (started slipping), when after I blew my first 427 engine while racing, we built the second (441 c.i., 14:1 compression, solid roller cam) BBC engine for it. That second BBC was too strong for the posi unit.
At that point, the Chevelle was race-only, so we installed a Moser (or Strange) full-spool differential (both axles are locked together), 4.88 gears, C-clip eliminators, and Moser 33-spline axles. It whined on coast, also, but that
harmonized well with the gear-drive (instead of a chain drive for the camshaft) in the engine.
It was a head turner when returning through the pits, with the engine loping and the camshaft geardrive whining (and 2.5" open headers) all making a great sound...everyone always looked.
Here's a post on
https://www.thirdgen.org/forums/tran...ons-drivetrain that gives some good info about gear whine
Also, heres a chart with gear teeth patterns, as a reference
