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Discussion Starter #1
My 85 p-type had badly worn bearings in differential - had them replaced and now have a high-pitched whine cruising at say 65 mph - whine occurs under slight load, OR when you let off the gas. Appreciate any likely causes, adjustments, etc. Have tried heavier gear oil, no diff (pun intended.)
 

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I only know that diff are the most difficult mechanical component to set in a drivetrain. Hopefully 'piratetip' user here will get you a good pointer. Bur I heard shims are at the heart at the adjustment.
 

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Changing the bearings can cause a small change in the ring gear offset or backlash setup so the pattern should be checked. Also if the diff was run for long with worn out bearings it can cause bad wear in the gears making them noisy once the bearings are fixed.
 

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@Funkycheeze has it right.

You can count on never being able to change bearings in a diff and not having to adjust:
-Pinion head shim
-Carrier side shims
-Solid pinion Spacer shims (if you used that)

The crush sleeve gets sloppy in these over time, they are all old and worn out.
If a lot of miles were put on the gearset in that condition the gear mesh pattern gets really wonky.
If you try to set one up properly, that gear mesh pattern will never be right again and could be noisy.

I've had good success swapping bad gearsets to good used clean sets and new bearings ect..
Most I build are silent in operation when done.
Though there are occasionally some that have a bit of gear noise, I attribute this to the strangely worn gearsets.

Did you use a crush sleeve or solid spacer?
Do you have the specs it was rebuilt to?
-Backlash
-Photo of the drive and coast mesh pattern with marking compound
-Pinion preload
-Carrier preload

I supply all of this info whenever I rebuild one, they require a very meticulous setup process and order of progression.
A mechanic slamming new bearings in one and putting it back together is never going to work right.

Again the previous two replies are on point.
Just adding my info to the mix.
 
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Any Mk2 with poly subframe bushings might exhibit a bit of diff whine around 60-65 KM/H (35-40 MPH) when just barely feathering the throttle even on new gears. Other than that there shouldn't be any noise.
 

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Discussion Starter #6
Any Mk2 with poly subframe bushings might exhibit a bit of diff whine around 60-65 KM/H (35-40 MPH) when just barely feathering the throttle even on new gears. Other than that there shouldn't be any noise.
Of course we did replace the subframe bushings - makes sense I suppose these firmer bushes would help transmit more noise! Thanks to all for the input - checking gears, shims now.
@Funkycheeze has it right.

You can count on never being able to change bearings in a diff and not having to adjust:
-Pinion head shim
-Carrier side shims
-Solid pinion Spacer shims (if you used that)

The crush sleeve gets sloppy in these over time, they are all old and worn out.
If a lot of miles were put on the gearset in that condition the gear mesh pattern gets really wonky.
If you try to set one up properly, that gear mesh pattern will never be right again and could be noisy.

I've had good success swapping bad gearsets to good used clean sets and new bearings ect..
Most I build are silent in operation when done.
Though there are occasionally some that have a bit of gear noise, I attribute this to the strangely worn gearsets.

Did you use a crush sleeve or solid spacer?
Do you have the specs it was rebuilt to?
-Backlash
-Photo of the drive and coast mesh pattern with marking compound
-Pinion preload
-Carrier preload

I supply all of this info whenever I rebuild one, they require a very meticulous setup process and order of progression.
A mechanic slamming new bearings in one and putting it back together is never going to work right.

Again the previous two replies are on point.
Just adding my info to the mix.
Thank you for the excellent advice - just what I was looking for; I am not doing the work myself but the shop is checking all these things. Gears looked great when reassembled but bearings probably had been bad for a while so hoping these can be reused.
 

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All excellent advice given above.

In my experience getting used gears to mesh quietly with new bearings is if not impossible near to it. The wear pattern is set with the old bearings and old settings. For best results new OEM bearings and new gears are recommended. I used non OEM bearings and although the specs listed were the same when the diff was redone with factory KOYO bearings the difference was noticeable which lead me to suspect that there is more to the bearings than the specs listed.
 
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