My rear axle had a whining noise. Not real bad, but noticeable. It would make the most noise while coasting, neither decelerating nor accelerating. I suspected a pinion problem and found it to be loose. It turns out that the pinion shim was breaking and being squeezed out.
The pinion shim sets the depth of the contact between the pinion and ring gear. Preload between the two pinion bearings is reduced as the shim squirts out. That leaves it loose.
It is hard to say if the same thing has happened to others. There were a few reports of leaking pinion seals. I am not sure how many might have just tightened up the pinion and moved on oblivious of the shim being displaced. Heck I might have even done something like that not knowing what was really happening. I am smarter now.
Why did this happen? The shim looks to be hammered out.
A little bench racing with a friend we proposed that the smaller diameter of the 7.625" ring gear may have been a contributing factor.
The second gen trucks with the standard transmission and those with the ZR2 high wide package received the larger 8.5" and later 8.625" axle assemblies. Rumor has it that was because of the shock loads applied by the clutch operated trucks and the larger tires if the RPO ZR2 option.
Could it be that the smaller ring gear diameter of the 7.625" axle delivers more force forward into the pinion? The bearing is smaller in comparison so the surface area of the applied loads smaller as well. I have not compared the angle of the twist on the pinion gear, but it does seem to make sense that a smaller ring gear could offer leverage and more force applied to a smaller surface. I have added larger tires and added shift firmness. Both may be taking a toll and hammering that pinion.
What would it have cost to fix this? nothing had been hurt. The bearings were all in good shape. When you are in this deep it makes sense to replace all the seals. Gasket and all three seals will cost under $20. The large pinion bearing will need to be pulled and will likely not survive the removal. That adds another $20. The shim is not expensive but may be difficult to find by itself. I am going to guess that it will be under $5 even less if you can get it from other than a dealer. You will also need a new crush sleeve $4. All together that should be under $50 worth of parts.
Could you fix this with out specialty tools? I think so. Carefully measure the remnants of shim that are left and choose one of the same thickness. You will need a torque wrench to set the pinion preload and a large dead blow hammer to install the carrier. Other than that everything should go back together with out too much difficulty. the pattern and depth should be as set up before and not need adjustment. You could use a dial indicator to measure clearance just to check if you like. I think you will be fine though.
Ok, mine went bad and I did not fix it why? I think the 7.625" axle is a good one. I have one in my older S-10 and with few problems in the last 200k miles. I treated it about the same as this one and it has held up just fine. It may not be a great comparison as it is a 7.5" differential running 4.10 gears. That could offer just enough difference.
The repair to this axle was not what I would call extensive. I had a good truss cover on it to help support the strength. I can not say I had a great reason to bail on it. If you still have the stocker and are not REALLY rough on it. You should be fine.
