Took my car out for a spin as it hasnt seen the light of day for a few months. Havent had the car out since I took it to the track in the spring.

Anyway, it has major diff whine on decel that it didnt have before the last trip to the track. 8.75 w factory r&p. Cone sure grip that has been cut and shimmed. Took the 3rd member out expecting to "see" something obviously wasted. But everything "looks" normal. Backlash eyeballs correct. Pinion nut tight.

Ideas on what it could be?

Most drag diffs are set up so that the wear pattern is more towards the inside(stronger)of the tooth. They do tend to make a lot more noise then a diff set up to factory specs. Maybe it wore in a little more and you are now noticing the noise? Using the Redline anti shock stuff helps. The ultimate "green goop".

Check the pinion nut, sometimes it can work it's way loose and give you a noise.

I understand the more noise, but this is past more noise. This is so loud that i thought the diff was coming through the floor it is so loud. My richmond geared chunk is not even close to this loud.

Nut is tight.

FWIW, the Dana 70 under my '01 Cummins Ram started whining bad on decel a while back. It had gotten noticeably worse and then I noticed it leaking from the pinion seal. The pinion bearings were worn real bad, along w/ the carrier bearings. When I crawled under it to drop the driveshaft, there was noticeable side to side movement on the pinion yoke due to the bearings...the yoke and pinion nut were tight.

Replaced the bearings, new pinion seal, all's good.

Chip.

I really thought pinion bearing when i first heard the noise. Bearing was replaced when I went through the 3rd member, for what little its worth. But no play and bearing "looks" good.

Guess the best thing would be, take it all apart, replace the front bearing or look for cracks in all the parts then re-setup with a good mesh pattern.

If the pinion angle is wrong, it will whine on decell also.

Make at least a .010" shim change. Set the back lash a little on the tight side - .006".

489 case? If so, standard pinion crush sleeve or solid (non collapsible) aftermarket replacement? Putting a bunch of hard launches on a 489 with an OEM-type collapsible spacer will eventually start to loosen the preload, from my experience.

489 with solid replacement.

Just don't let off the gas...... Problem solved

Does the wife-girlfriend ride with you? Make em mad, noise goes away.

I would replace the ring and pinion you did say last time out was the track.
1. How good was the traction on that day?
2. It is a 8-3/4 know to have ring and pinion failure.
3. Stock racers are replacing their ring and pinions ever 50 runs

A LOT of the gears made lately have been
making noise.. a buddy had his 8 3/4 done
3 times now in the last month(a pro shop doing
the set up) and each has been noisey as hell.
they kept saying bring it back and so far its
been 3 different gear companies... I dont know
about the last one that was put in.. that was
only a few days ago and I havent talked to him
EDIT
I havent had any problems with my 8 3/4 and its
been in the car for a lot of runs.. over 400(742)
with the alum housing