From the responses received it sounds like pinion alignment is something that should be investigated. How do you check for it and how do you correct it?
To give you slightly flippant answers:
- The way you check for proper pinion alignment is to listen to the differential. If a howl occurs when you unload the drivetrain by cutting back on the gas or giving no gas and coasting, but does not happen during acceleration, then you have an alignment problem.
- To correct it, you put it back to the way it was when it left the factory. Repair manuals give some specifications.
As an aside, a slight amount of misalignment won't cause damage, but will drive you nuts. With significant misalignment and enough miles, the differential gears will wear prematurely. Not having heard your differential, it's tough to say where you are on this scale.
When replacing the pinion seal, you DO NOT tighten the pinion nut back to new specification torque settings. You tighten it back to the same as it was taken off.
I think what Roadtrip is saying is that the nut needs to be returned to the same position the factory tightened it to; not set to a specific torque value. Finding that position isn't too hard, as the factory staked the U-joint flange to lock the nut. You can see the old stake marks, and set the nut to there.
the problem is as simple as the shop over-tightening the nut, and the remedy is backing it off to where the factory had put it. (admittedly this may be hard to understand without photos/diagrams).
Hmm - or is there a "crush washer" on the pinion shaft, and once it's over-torqued, the washer can't recover?