Rear main seal

Yes. You must drain the oil & remove the oil pan, then remove the rear main bearing cap & bearing. You then GENTLY push out the old upper seal half and reinstall a replacement. Remove the old lower seal half at the rear of the rear main bearing cap, install the new lower seal half , torque the main bearing cap in several steps to the factory torque, reinstall the pan with a new gasket, torque all pan bolts evenly and you're done.....But wait, there's more!

What leaks as often as the seal is the pan gasket at the rear main bearing cap. When you reinstall a new pan gasket get the one piece unit sold by the dealer (it's gray rubber.), put a good RTV bead on the groove in the rear main seal where the pan gasket seats, plus put some on the pan surface all along the rear of the pan, opposite the rear main bearing cap. Be sure to install the gasket FIRST, holding it in place with a few studs in the oil pan bolt holes (these keep it in place while you install the pan. If you do all this, and if you didn't FU the new seal putting it in, the fix will last about 25k - 40k miles before it starts to leak again. Live with it, it's part of owning an old Jeep!

Also if you have never had the oil pan off, the original gasket is a major pain in the rear to clean up and get off. Prepare to spend a LOT of time getting it cleaned off. KH

remove the transmission and the flywheel, it's lighter than an engine and there's less stuff to unplug

Either you're a real optimist or the luckiest guy around, unless your'e definition of GENTLY is a whole lot different than mine! Mine took a brass drift and a 4 pound hammer on top of lots of cussing to break that top half-seal loose! Of course this was an '88 but a '91 has had time to cook in, too.

Just be sure you get a brass drift punch - welding rod or a stick of brass from the hardware store just a little under a quarter inch will do - so you don't bugger the crank surface. It also helps to loosen the main bearing caps a bit but be sure you support the tranny on a jack to keep stress off the crank. You need to use a small amount of silicone sealer on the rear bearing cap ends of the seals so that they mate right - see the shop manual and I think even the Haynes manual mentions this.

Besides getting the pan off (it grows on, too) you will need to pull the starter for working clearance. The first time I had the pan off I spent a lot more time getting the old gasket scraped off than the rest of the job combined, including the time it took to finally bang the upper half of the seal out.

A little research will also make the job of gett> Yes. You must drain the oil & remove the oil pan, then remove the rear main

Dave Milne, Scotland '99 TJ 4.0 Sahara

Why?

It's a two piece seal...

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's

"MudPuppy1976

Yes.

You simply remove the oil pan, loosen the bearing caps, and remove the rear bearing cap.

That said, you have a leaking valve cover gasket, not a leaking rear main seal.

Most of the time the upper seal half comes right out, UNLESS some moron decided to use sealer on it, which may have been what caused Will's to be so stubborn. But, YES, be very careful not to nick the bearing surface while you're working the upper seal half out. I use an old chopstick to knock them loose, then pull from the other side with a pair of needlenose pliers.

Good idea.

The factory manual calls for Loctite 551 or some such sealer, turns out to be a high temp RTV, or so the dealer tech tells me. You are also supposed to seal either end of the cap itself with a very small amout of sealer.

This isn't necessary on later ones with the little Chrysler starter. It is on CJs', etc. with the larger Ford-type unit.

The factory YJ manual suggests making 1" studs to insert into the larger pan bolt holes on either side of the block. They suggests taking 1" long bolts, grinding the heads off of then and cutting slots in the ends. (Whew, lot of work!) You put the studs into the bolt holes on either side the block and slip the seal over the studs before installing the pan. They hold it in place while you muscle the pan back on. Not wanting this much work I simply went to the local hardware store & found some some threaded studs with slots in the ends and used them. Worked like a charm.

One last thought, be careful not to over tighten the small front-most pan bolts. They are very short and seat in the aluminum front cover. If you strip them out you'll have to pull the damper and replace the fron cover, which won't be fun..

Like I said, your definition of GENTLY... . Every one of these things I've ever done on on heaps has been pretty tight and there's usually a ring of hardened (baked?) oil on them. Once it moves even a little you're home free - it's that first little bit that's tough. For mine, I put a good half inch mushroom on the head of a 7/32 brass rod getting it out and almost that getting the one out of my son's '91 XJ. Definitely beyond the chopstick working range.

Slightly afield, but I don't recall any tabs on the seal halves - what keeps them from spinning over time? Just the friction in the groove?

There are tabs on either side of the lower half.

sorry, not thinking, you are right. i tried to cancel that stupid reply of mine, but it wouldn't do it!

What? Maybe in a lexus, but in a Jeep you just pull the bearing cap. KH

"MudPuppy1976

Wrongo. The lower half of the seal has tabs on either end that fit in grooves in the bearing cap. This is what differentiates the top half from the lower. If you use the factory pan gasket it's one piece. The older, 4 piece (POS) pan gasket has tabs for the front & rear pieces. I'd run from that version like it had herpes!

That four piece pan gasket bites the big one. It is the hardest thing to get on right I have done in a while. I wish I knew about the one piece when I did mine. Holy crap between removing the stock gasket and installing the four piece It was one heck of a miserable job. KH

Yep, permatex ultrablack is one of my best friends. KH