1990 Cherokee Front Differential Replace/Rebuild

[KirkLipscomb]

My 90 Cherokee has converted itself to 2WD. I took it to a tranny shop and they figured it'd be about $1200 to rebuild it. Now, since the car is not worth much more than $1200, that is pretty much out of the question.

I haven't worked on differentials before, so I have some questions about doing the job myself.

1. Can you get kits to rebuild the differential and is a very big deal to do? (I'm pretty good with engine repairs but have no experience with differentials or transmissions)

2. Should I look for a replacement at a wrecking yard? How hard would it be to swap them out?

3. Any other hints would be greatly appreciated.

It would sure be nice if we were back to 4WD land by winter!

Thanks,
Kirk Lipscomb

[Saudade]

You should probably 'splain a few things.

What symptoms are you having?

Are you sure it's the diff and not the Transfer case?

What did the tranny shop tell you is wrong?

[KirkLipscomb]

My daughter was driving on the highway and heard a "pop". After that, no more 4WD. I took it to the transmission shop, expecting to hear it was a transfer case problem. But, the tranny guy says it is the front differential.

[KirkLipscomb]

I forgot to mention - this breakdown happened during the winter on icy roads, so the vehicle was in 4WD mode at the time.

[Ray H]

Originally Posted by KirkLipscomb

I forgot to mention - this breakdown happened during the winter on icy roads, so the vehicle was in 4WD mode at the time.

Dont spend any money until you have a better idea what you are dealing with. Its highly unlikely the whole front end needs replaced. Its most likely one broken part and there are several parts that can easily and inexpensively be replaced. Here are a couple things that you can check if youve got an hour, a socket set, some gasket sealer, jack and jackstands, a flashlight, some diff oil and something to catch used oil in.
Look at your axle u-joints. You can use a flashlight but if one is broken, it should be easy to spot.
Start the Jeep and put it in 4WD then shut it off. Put the front end on jackstands. Rotate one wheel. The other wheel should rotate backwards. If this happens youve eliminated a problem with anything in your front axle except the ring and pinion.
If it fails that test, its time to investigate a little deeper.
I believe 90s had a vacuum disconnect on the front pass axle tube. You can id it by the two vacuum lines and a wire going into it. If these vacuum lines are leaking or disconnected, you wont have 4X4. If you pull the cover off that vacuum motor you will see how it works. Some oil will run out. Look to see if the sleeve and fork are not broken. With the cover off you can start the Jeep and move the transfer case lever back and forth from 2 to 4WD to make sure the fork moves.
Pull the diff cover. Lots of oil will run out. Look the ring and pinion gear over for damage Look to see if there is metal laying in the bottom. Look at the spider gears in the diff. If your spider gears are busted, you can easily replace them in your driveway but if that is the problem you should do a real good check for damage to your ring and pinion.
To check that one of your axleshafts arent broken, you will need to rotate each wheel while someone watches for the spider gears in the diff to turn. On the pass side you need to have someone watch in the vacuum disconnect cover for the outer shaft to turn, then reach in and turn the inner shaft and watch it at the diff.
These checks are free and will tell you exactly what is or isnt wrong with your axle. If it all checks out, youve got a transfercase problem and you now know your mechanic is full of crap and you should avoid him in the future.

[Saudade]

Like Ray says, it's easy and cheap enough to check a few things yourself. For all we know, you lost vacuum and the pop was just the differential disengaging.

[KirkLipscomb]

Thank you very much for the tips. I will try to have a look this weekend if my daughter can turn loose of it for a day.

[KirkLipscomb]

I finally got a chance to tear into this project.

First, there was a problem with the vacuum switch. One of the vacuum lines had gotten brittle from age and had cracked. Got that fixed and the fork moves like it is supposed to now.

But that didn't solve my problem so I opened up the differential. Sure enough, there were bits of metal all over the bottom. The ring gear has some broken teeth. None seem very bad and it turns fine when a wheel is turned. The problem is with a gear in the back of the differential, where the drive shaft attaches. This one has disintegrated.

Any thoughts on how much trouble that gear would be to replace? I'm going to dig through the service manual tomorrow, but it's always good to hear from someone who's been there.

[AlohaBra]

Yeah..that is the pinion gear...see if you can get a whole 90 XJ front axle from a salvage yard...or internet search.
Swapping in other years can be done also with a little more information....it has to do with vacuum switching, linkage, etc.
Replacing the ring and pinion can be done also... Now...find out how much used or new stuff will cost. The job is easier but heavier than engine work. Added cost for rebuild...oil, seal, bearings...tools, like torque wrench....also sealant.

PS...taking the axle out to work on it or laying underneath to do it depends on how your body likes working and doing contortions while working on machinery upside down. With air tools and no lift, I would take it out. With a lift, I would leave it in.

Best regards,

[MrEleven]

Check into NAXJA.ORG It is the biggest cherokee website i have ever been to. Everything you have ever wanted to know the have already discussed it. Chances are that someone may live close by and you can go pick up what you need.