Rebuilt 8.75 whining

[64dartgt]

I just had an 8.75 totally done.  Sure-track was rebuilt and new 3.55 Motive gears and grean bearings were installed.  When I let off the throttle I am definitely getting some gear whine.  The Dif guy suggested Motive's over Richmonds because he said that in his experience the Motive's were quiter.  I called him to discuss it and he confirmed that I was hearing gear noise and that it was just the way the gears were made.  It could get a little better as they break in, but if it gets worse to bring it in.  He also said I could bring it in so he could check it out just for piece of mind.

Any opinions?   

[Chryco Psycho]

He didn't set them up right !

[64dartgt]

I hope not!  I went to Mitchell Differential.  They have been around forever.  I appreciate the comemtn though, and will take it to him so he can check it out.  I spent a lot of $ on it and it should be right.  Luckily it is an 8.75 so he can just pull the pumpkin.

[Chryco Psycho]

well the gears have to mesh in exactly the pattern they were machined for , this requires setting the pinion at exactly the correct depth using shims behind the bearing , then adjusting the ring gear side to side , the pattern is usually checked with a lead compound the catch is they load side is one side of the teeth which everyone checks , the coast side is the opposite side of the teeth , both have to be right fro the gears to be silent , he may be off on the mesh on the coast side

[Cooter]

I seem to recall posting in this thread elsewhere about the Green bearings as they tend to not like side loading around turns. Might wanna check into having them "Un-installed" if they are the thinner style, "Ball" roller bearings as well..

As for the gears whining, if I paid the guy and wasn't happy, I'd be going back to him...

[64dartgt]

I called and he is taking the car next week to look at it.  He doesn't seem to think it is his fault (set up), but said he could swap the gears for another set.  We'll see.  At this point I have so much money in the car I'm damned if I am going to listed to the whining instead of the rebuilt 340 for the sake of a few hundred bucks. 

[Brickster]

sometimes you can do everything correct and gears just make noise.

[Nacho-RT74]

sometimes you can do everything correct and gears just make noise.

I think thats my case!

[Challenger340]

I just had an 8.75 totally done.  Sure-track was rebuilt and new 3.55 Motive gears and grean bearings were installed.  When I let off the throttle I am definitely getting some gear whine.  The Dif guy suggested Motive's over Richmonds because he said that in his experience the Motive's were quiter.  I called him to discuss it and he confirmed that I was hearing gear noise and that it was just the way the gears were made.  It could get a little better as they break in, but if it gets worse to bring it in.  He also said I could bring it in so he could check it out just for piece of mind.

Any opinions?   

Some simple diagnostics...

If the whine is only on "deceleration", it would suggest a REAR pinion bearing or Pinion too deep into mesh, because the Crown gear tries to throw the Pinion OUT OF MESH during decel which loads the rear pinion bearing....
conversely,
Whine during Acceleration, is indicative of a Front Pinion Bearing problem or Pinion too shallow into mesh, due to the Crown trying to Drag the Pinion INTO mesh under load.

Your Guy "missed" when attempting to hit the "sweetspot", or reccomended Pinion Depth.
Now,
Depending upon how LONG the gears have actually been driven or "exposed" to wear under load in the incorrect position, they may or may NOT be able to be reset correctly. 

[bakerhillpins]

How do you like that... my 8.75 whines on decel so I guess I have something to look into but ill just live with it for now as I suspect they have been in there that way for a while (just bought it) so a rebuild would probably be required to correct it.

[gtx6970]

sometimes you can do everything correct and gears just make noise.

yep

[64dartgt]

Some simple diagnostics...

If the whine is only on "deceleration", it would suggest a REAR pinion bearing or Pinion too deep into mesh, because the Crown gear tries to throw the Pinion OUT OF MESH during decel which loads the rear pinion bearing....
conversely,
Whine during Acceleration, is indicative of a Front Pinion Bearing problem or Pinion too shallow into mesh, due to the Crown trying to Drag the Pinion INTO mesh under load.

Your Guy "missed" when attempting to hit the "sweetspot", or reccomended Pinion Depth.
Now,
Depending upon how LONG the gears have actually been driven or "exposed" to wear under load in the incorrect position, they may or may NOT be able to be reset correctly. 



The whine is worst under decel, but slight still under weak accel.  He is going to pull it and adjust the pinon depth a few thou, as you suggest.
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[Dino]

Interesting....my rear axle has a slight whine between 35 and 40mph, under or over that it goes away.  When I release the throttle it also goes away.  Weird.  I'll have to fix it cause that's backroads cruising speeds!

[64dartgt]

Latest is that my guy did what was suggested, shimmed it out a bit more...but it got much worse.  My conclusion?  After much online research I am pulling the Motive Gears (tried to talk to them but the Tech Mailbox was full...not a good sign)...and going with either Nitro or Yukon.  A few more hundred is worth it for peace and quiet!