Rear drivetrain inspection questions.

[Timothy B.]

Rear suspension is apart with the bearings sent out for rebuild. I removed my half-shafts and am inspecting the U-joints. These joints are probably 20 years old, but have probably only a few thousand miles on them. Per posts on this site, I inspected some of the end caps and rollers and the grease is good and I see no apparent wear. Rubber seals look OK too. These are the type with grease fittings. I know some folks say replace them anyway, but I'm thinking that these are just fine to leave in place. What do you guys think?

Also, on another note, is it normal for U-joints to create a small grease pattern on adjacent fiberglass surfaces? The last time I greased the joints I tried to avoid over-doing it, but they still fling a little grease. Is that typical? For joints with fittings, how much grease should you inject?

I will probably replace the drive-shaft joints since I am not sure when they were ever done, unless of course when I take them apart they look fantastic.

Lastly, on the differential: I am planning on leaving it along for now since there are no leaks, front seal has been replaced as was the clutch pack some time ago. How much in-out play should there be in the yokes that attach to the half-shafts? I can pull in and out of the yokes and feel some slight play, with one being greater than the other. Should I be able to notice that play by feel?

Thanks!

[Duke W.]

Re: Rear drivetrain inspection questions.

It sounds like the U-joints are serviceable. Given the mileage you accumulate there is virtually no need to grease them. That's why GM used joints with no grease fittings. It's would be tough to not "overgrease" them, and if you do they will likely fling the excess. At a few thousand miles a year, greasing them about every 10 years should be adequate.

There is no differential side yoke end play spec, but a properly assembled differential with dimensionally conforming parts should be less than .010". Once end play increaes to about .030" the Positration clutch pack is worn, or the yoke ends are worn, or both.

Use a dial indicator to get an accurate measure of yoke end play. Since the rear suspension is off, it's not that much work to drop the differential cross member, remove the diff. and remove the back cover for an internal inspection, including removing the yokes for inspection, checking differential gear backlash (which, if excessive, indicates clutch pack wear), hypoid backlash, and smooth running of the bearings.

Duke