I hav noticed in the last year that my rear end while roar/whine while accel/decel etc. But my question is last year while pulling out my buddys chevy his tow hook broke and put a hole in my rear pinion cover. So i drained the oil and and installed a new cover. I put the called for synthetic oil in it but I didnt know to add any friction modifier. Should I do this or not? It is the 9.75 LS rear. Or maybe my pinion bearings are gone?

 

A whine on coast indicates a pinion problem. Could be bearings going bad, or just worn to a point of having a no pre-load condition on those bearings.

A way to check: Take drive shaft off and rotate the yoke around and feel for any roughness or a drag/ flat spot. If OK check preload on the nut with inch pound torque wrench. Wheels off for the check.

All clutch limited slips to my knowledge need the additive, though the lack of additive is completely unrelated to the "whine."

 

LS rear end requires friction modifier.

 

but not having the friction modifier have caused maybe the bearings to whine? The truck has 96k babied miles on it. But for about 50k miles it has had 35" tires.

 

No, the modifier is only for the clutches. Lack of modifier will not affect any of the bearings.

 

For clarity, the bearings do not whine. The worn bearings, if this is the case here, allow the pinion to drift in the bearing race, causing it make contact to the ring gear to be 'inconsistent' or unstable. In other words the contact point or the *mesh* varies --- it is not rock solid centered.

Hence it vibrates a harmonic like a tuning fork.

If you have the torque wrench and the motivation, the check that was outlined is solid way to find out where you are at.


This is a heavy truck( long bed), with tall tires. Quite a load to haul around for that rear end gear.

This would be a starting point to look.

 

now if i stop on a hill and turn right or left the rear end will shudder. I checked the fill plug and there was a good bit of metal on the end of the plug.What should I do next? Thanks

 

The shuddering could be a by chatter from not having the modifier added.