hum or howl in 4wd

TrybalRage said:

I used my 4wd for the first time in a while during a snowstorm a few weeks ago, and these symptoms don't give me the warm and fuzzies after reading this.

In 4wd hi or auto - slight growling low vibration under acceleration, stops when foot is off the gas.
Goes away completely in 2wd.

Crap.

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Yeah, sounds pretty familiar. I just took my carrier out tonight and tomorrow will put in the replacement unit from LKQ. I split the two halves and looked inside, but haven't seen anything crazy obvious yet. I'll do some more checking tomorrow and report back.

Guys - I'm thinking since I have the diff out a second time, I'll go ahead and do the oil pickup tube o-ring. My oil pressure seems to be getting worse. It's just over 20 psi at highway cruise RPM now. Seems pretty low. I bought a Fel-pro oil pan gasket and o-ring today, so I think I'm ready. How hard is it to drop the oil pan? I know you have to get the timing cover off to get to the actual pump, but it looks like you DON'T have to do that if you're just replacing the o-ring? I know you do have to lower the steering rack to get the pan off, but that doesn't seem too crazy....

If anyone has any thoughts or advice for this one, please let me know.

You should not have to remove the timing cover, no.

I put a junkyard 5.3 in my C10, and I replaced the pickup o-ring on that before I put it in the truck - I never took off the timing cover. That was a gen3 motor but I don't think it should be different.

I have no idea how hard it would be to get the pan off with the motor still in.

Everything put back together and voila!, no more noise from front diff. Can't hear the difference between 2wd and 4wd (auto or high) at all. And as discussed previously in this thread, this time I went the extra step of dropping the oil pan to replace the pickup o-ring. Now my oil pressure is a good 5-10 psi higher for a given rpm/temperature. The trifecta would be if replacing the pan gasket (Fel-Pro) resolved the small oil leak that has annoyed me since I've owned it. I'm optimistic since I'm pretty sure it was in the corner where the oil filter is, and it sounds like leaks there are common.

swathdiver said:

Sorry Dave. I'd go with them again too. Lots to choose from and reasonably priced.

I "think" the difference is that older one has a single seal flange and the other a double seal flange. In the grand scheme of things, who cares? Get whichever is most convenient with the lowest miles and in the best condition.

I was fortunate to get one from Suburban a year older but with less miles than mine.

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James, in looking at them side by side (sorry forgot to grab a pic) I think you're correct. The hub where the stub shafts slide in was a good bit bigger on the newer version, so a double seal is probably a good bet. I'm pretty sure the passenger side extension is swappable between the two, so I COULD use the newer if I ever need to, but I seriously doubt it.

I took apart the removed carrier, expecting to find obvious damage, but I don't see anything ground up. The only thing that seems no bueno to me are the bearings the diff rides on are loose, but they're fully intact. If I needed to get this one going again, I'd replace those bearings and probably the ones for the stub shafts and put it back together. No damage to the R&P, and the pinion bearing seems solid, smooth, and tight. There are some weird marks on the open faces of the diff, but in closer inspection (and thinking about it) it seems that are just indicative of some not great factory machining.

bearing looks like it got hot. IMO change it and any others that look like it.