Diff whine during deceleration

[nine2oneGT]

Been driving my 2000 GT around to break in my new motor. I had FRPP 3.73 gears/rebuild kit and carbon disk traclock installed. Dyno tuner had noticed that there was a whine coming from the diff when the car is decelerating under load. If I take it out of gear and coast there is no whine, or it is very quite. There are a few rumbly spots in the gears but no other noises or symptoms. I opened up the diff last weekend to check the gears and clearances at my uncle's auto shop. The techs said that everything looked great. I replaced the oil with royal purple 90-175 i think. Whatever came with the FRPP kit, and friction modifier.

Not really familiar with drive train diagnostics and problems so any help would be greatly appreciated. The noise is definitely coming from the rear of the car so I do not think it is the tranny. Idk if there is any kind of break in for the gears or lsd.

 

[nine2oneGT]

BUMP - Anyone?

 

[usaf_branham]

i wouldnt worry about it at this point because your gears have already machined themselves for the pattern it was set at. if you try to change backlash, pinion depth, etc now its most likely going to whine worse.

 

[nine2oneGT]

Any ideas what parts of the diff come under pressure just during deceleration?

 

[nine2oneGT]

Im going to try a diff oil called Redline Shock Proof. It is used in heavy duty and off road applications. Read around on some other forums about guys with the same issue and this oil reduced the noise created.

Ive been reading differing opinions about whether it could be fixed or not. Im going to try this oil and if it doesnt help I dont know what im going to do. The noise is not that big of a deal but I am noticing a pretty good rumble around 1400 rpm in all gears. Everywhere else it is very smooth.

 

[03_TrueBlue_GT]

I have FRPP 3.73 gears and I hear gear whine sometimes when I decelerate, you really have to listen for it though. How many miles have you put on yours so far?

 

[nine2oneGT]

03_TrueBlue_GT I only have about 500 miles on them so far. I think it was louder at first but I can still hear it pretty easy.

 

[vertigasen]

Wait. It is the worst around 1400 rpms in all gears? That is interesting then, because the rear diff does not spin in relation to rpms.

 

[nine2oneGT]

vertigasen ......yeah, I have already been shopping around for trannys. I know there is some weird ass knocking noise in it sometimes. I cant hear it inside or outside the car but I did when I put a stethoscope to it. It goes into all the gears fine but definitely can feel something around 1400.

Im thinking about getting a T-56 with a HD rebuild. I would get 1-3 cryo frozen.

 

[trinity_gt]

During deceleration the outer pinion bearing is loaded more and could be a source of noise on the overrun.

 

[blkstanger]

I don't think I would run the Redline Shock Proof. That stuff is 75/250 or something like that. It's real thick stuff. I use it in Harley gear boxes. It looks like Pepto bismal when you pour it. To thick for a Mustang rear end IMHO.

 

[nine2oneGT]

blkstanger Yeah i know it is rated higher than the normal 175 but Redline claims "Film thickness greater than an SAE 75W250, yet low fluid friction like 75W90". I live down in Texas so it doesn't freeze really. Im going to check it out and see if it helps at all.

 

[nine2oneGT]

trinity_gt That could be it but it is a brand new bearing.

 

[trinity_gt]

That may be but if the setup was wrong -- wrong pinion preload, wrong backlash, bad pattern -- the assembly will make noise.