89 rear end troubles

[Bard Skye]

I have a stock 89 Cherokee Laredo 4.0 liter with auto / selec trac and a Dana 35c rear end.

Immediately after deer season, (I was using L1 and L2 a lot for speed control on the logging roads) I started hearing a noise coming from (apparently) the left rear axle. I thought that an axle bearing might be going south, but I could see no oil leakage and there was no play or rotational roughness that I could detect. Within a few days, this changed to a rumbling, pulsing noise that pretty much went away while accelerating and would immediately return as soon as I let off the gas. The last time I heard a noise like that was just before the rear end of the truck I was driving siezed up.

I pulled the diff cover, expecting to find broken teeth and metal shavings, but found a nearly perfect looking diff. The oil level was a tad low, but everything was well coated with oil, so I don't think this was a problem.
There are slight burnish marks on the ring and pinion teeth, but nothing beyond normal wear. Tooth engagement is good, and there is no play in the pinion shaft. Lash is minimal, although I can't find my feelers to get an actual reading.

I pulled the axles to check the bearings, and they're fine. No roughness, pitting, and they rotate smoothly.

With the axles out, the carrier rotates very easily and smoothly with no play in the bearings.

The spiders feel a bit stiff, but nothing unusual. U joints are well lubed and mobile with no play.

I'm stumped about this noise.

Any ideas?

[fredjacksonsan]

Sounds like a driveline issue for sure. I've heard of sounds seeming to come from the wrong end, how is your front driveline?

Also, is your transfer case definitely out of 4wd? If it's stuck IN, then it would cause driveline noise.

How many miles?

[Bard Skye]

The ol' girl's got 223K miles showing on the odo. Considering I bought her used, who knows what the number *really* is. (and I'm not so impolite as to ask a lady a question like that!)

I haven't really checked out the front end yet, although I know the axle u-joints need replacement. (They click in turns while in 4wd)

The transfer case is definately in 2wd, however. So at least *that's* not the problem.

I guess I'll hear what it sounds like when I put it all back together tomorrow.

BTW, I found a tag attached to the diff bolts next to the ID tag. It said to use limited slip diff oil, even though it's an open diff. I don't know what it was filled with, but would this make a difference?

[fredjacksonsan]

When you said the spiders were stiff, you did mean the spider gears in the diff, right?

You said it's more of a rumble now; if it were Ujoints it would be more of a chicka-chicka-chicka noise, so those are likely ok. Rumble could be a lot of things, from the diff to axles but you've already inspected those. It may be time to check the output shafts, but I'm thinking that it's the front.

Can't be sure of what it is though, but you might be able to locate it more precisely by either putting another pair of ears on it, or jacking up the entire vehicle and seeing if you can reproduce the noise while it's up - if so, it should be easy to locate.

[LittleHoov]

How fast are you going when these noises happen? Or does speed make a difference.

How about turning one direction or the other, any change in the noise?

Front hubs can act like what youre describing, no noise when accelerating, but when you let off and more weight goes back to the front, they start making noise again.

[Bard Skye]

>How fast are you going when these noises happen? Or does speed make a difference.

Gets louder at speed, pulse frequency increases with speed.

>How about turning one direction or the other, any change in the noise?

No noticeable effect.

>Front hubs can act like what youre describing, no noise when accelerating, but when you let off and more weight goes back to the front, they start making noise again

No noticeable acceleration required. Just the throttle changes neccesary for maintaining highway speed.

[Bard Skye]

Found out why the spiders were stiff.

Called up the local dealership and ran the numbers past the parts guy. He tells me that even though it *looks* like an open diff, it's actually a limited slip. The clutch packs are hidden down in recesses in the ends of the carrier. Never seen anything like *that* before.