wwilkjr@gmail.com

So, there is a very distinct buzz/whirr/grind noise coming from my rear differential. Took off the diff cover, all gears are scrape/gouge/crack free. VERY minimal glitter on the magnet. My transmission knowledgeable buddy says he sees no reason to rip it apart if there is no damage or excessive wear. A mechanic at a shop says the Only way to truely diagnose it is to rip it apart, and if he does that, I should be prepared to spend $600. He also said the other option is to drive it and keep an eye on it. The Jeep did sit for quite some time, barely being driven before I bought it. My trans buddy says maybe there is a little corrosion on the bearing, and it could work itself out. What do you guys think?

94zjdriver

a few thing to check..
\Does it whirr when giving it the gas or coast, if so very well could be worn gears.
/ Does it whirr constantly or faster with speed, if so very wellcould be bearings
/ does it whirr more or less in turns at speed like interstate on ramps, if so which side, if so will intecate axle bearings left or right.

If it is bearings fix it before something really goes wrong, as in wearing a grove on the axle or Pinon and have to replace thoes as well.. Bearings usually do not get better with time. only worst.

If it is gears it may last 2 days or 2 years depends on if you can stand the whirr and if it gets worst. I have ran whirring gears for a long time and i've had them go in a couple of weeks after they started to make noise. I rebuilt rearend could run 4 to 600 depending on the shop. You can replace the outer axle bearings yourself and save some dough but if you've never did a rear end gear change its best left up to the experts.. Not saying it can't be done, it can, just need special tools and a work shop/

Just my 2 cents.

caged

i'd trust your transmission guy. he has the right idea.

my guess is either the same as the tranny guy, or your wheel bearings are on their way out.

does the sound dissapear when you let off the gas?

wwilkjr@gmail.com

The sound is related to the speed of the vehicle. It is loudest when I'm decelerating, and at low speeds, although it can be heard at higher speeds. It's not a wheel bearing. The sound is definitely coming from the rear differential. No doubt there. I have removed the rear differential cover. There is almost no glitter on the magnet at all. The gears are definitely not worn. I spent almost an hour examining them with a flashlight. That's exactly why Darrin (tranny guy) outright refuses to take the rear differential apart. Harm (mechanic) is afraid to give me advice, based on the evidence. He just gave me two options. 1) Keep driving it and see if it gets worse, or is a phantom noise that dissapears after time. 2) Have him disassemble the rear end, and examine each individual part, and be prepared to spend up to $600 on repairs.

wwilkjr@gmail.com

I have decided to plan for the worst possible situation and search the junkyards for a new rear end. My question now is, how can I tell which rear end will work for my wj?

PatriotGT

I'm tinking 99-05, could be wrong. The jy I used wanted my vin number
to match it up. Just make double sure you get the right ratio.
There are some links on here somewhere, where you can email Jeep
and get the build specs for your GC. If I run up on it again, I send it to
you.

found it:
http://www.jeep.com/wccsapp/universal/J/index.jsp

caged

yup, it sounds like a bad pinion bearing to me.

wwilkjr@gmail.com

Pinion bearing is what I was thinking, but wouldn't that cause damage to the ring and pinion gears?

wwilkjr@gmail.com

My plan is as follows. I'm going to buy a new rear end from a jy, they come cheaper than expected. I'm going to begin rebuilding the jy one, amassing tools and excellent knowledge in the process. That way, if/When the diff goes out, I just replace it.

caged

usually if there's in/out play. but you have two bearings, an inner and an outer. so chances are it could last a while, but there's the off chance it could lock up on ya at any time.

good call on finding a jy replacement. just be sure to get the right one.

wwilkjr@gmail.com

Thanks. I Have a buddy running a vin search for me, and some ears out. Jeeps are pretty common around here, and there are a lot of junk yards. I'm hoping that here is just a little corrosion on the outer pinion bearing and it will burn off after time. But, this way, worst case, I have a back up differential. Nothing wrong with that!