Rear Differential Question

My rear differential is leaking around the plug area so I've got a new plug to replace it with. I don't know what kind of fluid is in the rear diff but I'd like to top it off since I've lost a little bit. I had it changed a couple years back (~20k miles ago) but I don't know what kind of fluid they used. If I'm just topping it off to replace whatever seeped out (it's not leaking a ton) does it matter if I use a synthetic blend? I have a bottle I bought with intention of changing the front diff but ended up paying someone to do it (was in the shop for a slew of things). It's the right weight but it's synthetic..

Thanks!

This may not be the easy answer, but since you are at 20k since the last change, I'd drop the cover and change the oil completely. I think the cycle for oil changes to the diffs is supposed to be every 15 to 30k depending on level of use. You're right in that range.

yeah I think you are right, but I don't feel comfortable doing it myself. What do you think about for the short term ~ 5k miles.. that will get me till we have to put it in the shop for a few more things.. fyi we drive about 10 - 12k miles per year

Gear oil is gear oil, mix and match as needed.

Following proper maintenance schedules allows you to diagnose and repair little problems before they become big problems and also extends the service life of your vehicles.

Emerscape said:

yeah I think you are right, but I don't feel comfortable doing it myself. What do you think about for the short term ~ 5k miles.. that will get me till we have to put it in the shop for a few more things.. fyi we drive about 10 - 12k miles per year

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It's actually quite easy to change the oil, all you need is one socket an oil catch and some RTV and your good to go. Plus you'll be that much more familiar with your XJ. As for the gear oil, I've mixed and matched gear oil with no I'll effects however if you have a limited slip diferential you need to stay with a specific weight that has friction modifier added to it. Chances are it's an open diferential though so you shouldn't worry about it, top it off, put in the new plug and hit the road Jack!

As everyone else said, it's pretty easy. You're not actually working on the gears so no worries about precision really - buy yourself two or three cans of brake cleaner and a crappy set of plastic putty knives, pull all the bolts out of the cover (except the top one, loosen that one but do not remove yet), put a large drain pan under it, whack the side of the cover a couple times with a rubber mallet, let it drain. Pull the last bolt, then swab the cover down, hit the edge of the cover and case with brake cleaner, scrape what's left of the RTV off, hose everything down pretty well with brake cleaner (make sure you get any sludge and metal powder out of the bottom of the case), let it dry out, then put RTV on the edge of the cover around all the bolt holes and between them, slap it on, bolt it finger-tight, wait till the RTV is cured, crank the bolts down to 10-15lbft, fill er up and you're all set.

When you have them serviced at a quicklube (definitely) or the dealership (I believe) they use a vacuum line to suck all the old gear lube out of the case without opening it, then fill it back up. If you can get a suction setup that'll work well enough to suck used gear lube through a 1/4" poly line, it'll work great.

Thanks for the help guys. I think I'll go the "suction" route due to the fact that I live in the city and it's pretty hard for me to find a place that I can work on my jeep. I do have a parking garage where I keep the jeep that is pretty empty during the weekends so I could probably suction it out there, although I'm pretty sure they wouldn't be happy with me if they caught me.

Good luck sucking gear lube in the winter! It get's VERY thick. I warm up the new stuff in the house before I try to refill it. Synthetic probably won't be like that.

If you are just leaking a little around the fill plug, I wouldn't worry about the oil being low. The fill plug is also the level plug. It can't leak out if it is below the full level anyway.

Sorry to thread jack but W(where)TF do you buy a new rear fill plug for a C8.25?

Junkyard, they will look at you funny and tell you to take it.

Or buy 5207 0428AA at the dealer, it'll run you 4-7 bucks.