jon-d

I posted a similar question in another section but not much response since I own a grand.


anyway, i cannot figure out if its my trans or rear diff that is slipping. when first starting out in the morning (cold) the jeep will "jerk" or slip a little when starting out. once it warms up the symptoms are gone. But, when on the freeway going up an incline (not steady throttle level driving or downhill) the RPMs will jump up about 700 RPM then the trans/diff seems to catch (within a fraction of a second) and go back into gear. when this happens i hear a clunk in the rear diff, but that could be from the re-engagement of the power to the wheels. i have changed out the trans fluid and the old fluid was not badly discolored nor did it smell burnt. after driving for about an hour on the freeway when i stopped i check the rear diff and it was really hot, or at least so hot I could not keep my hand on the housing when I placed it there. certainly much hotter than the front diff.


this is a new to me jeep, so i don't have the history, and i don't have any idea what is in the rear (limited slip, locker?). sorry about the long post, what do you guys think? tranny going out or possibly the rear diff?

dave1123

First of all, differentials don't slip. I'd say your trans clutches are shot. The clunk you're hearing from the rear end is probably worn gears taking up the drive when the trans grabs again. My 97 did this, anytime you added too much power in top gear, it would slip or even low gear if you jumped on it. When we took it apart to rebuild it, all the clutches were toast and even the clutch drum had to be replaced.

Check the fluid level in the rear diff. Check the gears for backlash. You should not be able to turn the pinion more than 1/16" either way before the wheels will turn. My 97 had been ridden hard by a couple of soldiers before I got it and they really beat it. The trans was shot and the rear axle whined. They were about to be deployed and the price was real cheap. I should have known! The 4.0, however, purred like a kitten.

XJlimitedx99

Definitely the trans. The differential has gears whereas the trans has clutches.

jon-d

thanks guys. I was afraid that would be the case. I am not that familiar with the rear end so I was not sure. is the temp in the rear end that I described normal?

dave1123

With the 242 t/case in 2wd, it should be warmer than the front diff, but not hot. After a high speed run, I'd say it should feel like a hot cup of coffee that you can hold in your hand. As I said, check the fluid level and condition. Full, it should be up to the fill plug hole or within the first joint of you finger. It should not be black or have shiny particles in it.

jon-d

thanks Dave. it has what looks like a plastic plug for a fill hole, do I just pry that out and is it reusable?

dave1123

Yup, just pry it out with a screwdriver. It can be used until it tears or cracks. If it starts seeping around the edges, it needs to be replaced or it's overfull.

jon-d

checked the rear diff oil last night and had plenty in it. it might have bee a touch overfilled if anything. so I am not sure what to do at this point with the diff.


the trans however, should I look to rebuild it or replace it with something from the JY? I think the rebuild will cost me around 2500 (very good mom/pop shop I know). at how many miles do the trans normally go bad?

dave1123

The trans is only as good as how it was treated and maintained. Some people say the 42re is not strong at all, but mine has 195K on it and is still in good condition. The first 10 years of it's life (125K) it was driven by a soccer-mom, garaged at night, and serviced regularly. It had a full fluid flush just before I got it. I put another 25K on it before I did a filter and fluid change and I found nothing in the pan and no debris on the magnet, just a little fuzz. I drive it hard, but don't abuse it with instant reversals or high rpm engagements. 3 nights a week, it's loaded with newspapers and delivered mailbox-to-mailbox to around 300 customers with stops and starts all night. When I do a quick highway merge, it shifts quick and clean with not even a hint of slippage. Stepping out to pass, it steps out smartly. I use 2nd gear descending steep hills at around 30 mph without problems.

I'd have to say you'd be better off rebuilding the one you have because then you'll know the internal parts are good. Buying a used transmission is a shooting match that sometimes shoots back, lol. Going the cheap way out, you get what you pay for. JMHO. Don't skimp on the repair, install a new torque converter.

About the diff, pull the cover, wash it out, and inspect it for worn gears and bearings. After that, you can make a decision about what to do with it. The D35 is not the strongest kid on the block, but remember the ZJ was designed as a street people mover with off-road capabilities. It wasn't designed to go thrashing thru the woods or mountains. Well, maybe, lol!