maxflex540

275,000 miles. Front bearing/seal on the rear diff is leaking gear oil, I can move the input shaft up and down slightly by hand. Also there is a ton of gear noise at about any speed over 10 or 15mph when I have my foot off the throttle and its just coasting. There is so much gear resistance, that it slows the pickup to a complete stop as if I was braking, then after stopping it will roll backwards a bit as if you bumped into a parking curb or something. This all started very suddenly as I was driving at highway speeds.


So my question is how difficult is replacing the front bearing? I am looking for a parts diagram/breakdown somewhere I can look at. With the apparent high gear resistance and gear noise, might there be more wrong inside than just the front bearing? Or would the bearing having gone out dropped that shaft enough to change the gear lash enough to cause all the noise and resistance? Also, I don't know what gear ratio I have, and I might need to know for when I order parts?

Kawabuggy

the "front bearing" you are referring to is called the outter pinion bearing. Under acceleration the pinion gear is being forced towards the front of the vehicle and that small outter pinion bearing is unloaded. However, under deceleration, or when you are off the gas, the angle cut of the ring gear teeth is trying to pull the pinion gear towards the rear of the vehicle which loads the outter pinion bearing. That's why you hear it when you are OFF the gas.

This is not something an average mechanic can fix at home. The differential needs to be torn down and inspected by someone qualified to repair differentials. The bearing being that bad means most likely there is metal contamination throughout the entire diff. It *might* need all new bearings internally, new crush sleeve, new pinion seal, new ring & pinion set, and then be set up professionally so back-lash, and bearing pre-load are all correct.

Or, you *might* get lucky and just need to replace the outter pinion bearing & race, new crush sleeve, all metal cleaned out, new fluid and be on your way..

The only way to know which option is for you can be determined AFTER tearing the differential apart. Again, not a job for an amateur. Requires a host of shims, and special tools, and dial indicators, to properly set up a rear diff. Here is what I would do;
1. Open up your diff and determine how bad the damage is.
2. If damage is minimal and you think the other parts can be saved, then repair existing diff.
3. If it needs everything internally, just buy a used diff from a salvage yard and replace the entire axle as an assembly.

Keep in mind the China gears (ring & pinion sets) that are being advertised everywhere are JUNK! That's why it might be a better option to just stay with an ALL GM rear diff from the salvage yard, and it *might* be cheaper than repairing/rebuilding your existing axle.

You have an 8.6" rear diff and I rebuild them quite often-2-3 a month, every month. If you have any specific questions, please feel free to ask.