I can't believe this.....Rear Main Seal!!!

As you have probably noticed I bought bought an 88 MJ almost 2 weeks ago. It did not run, so I hauled it home from SC. The truck had not been cranked in about 4 years, so I expect a few problems. I got more than I expected. The paint is faded, but the truck has very little rust. Both floor pans will need replacing and the gauges / electrical will need some work. It is the major mechanical issues that I was hoping to avoid.

Aside from a new batter and new battery cable, the first problem was that the fuel pump was shot. I ordered one from RockAuto and installed it on Friday. The pump worked and the truck cranked. That was when I discovered that the O-rings on the fuel injectors were shot. Gas leaked like crazy. I also discovered the valve cover gasket leaked badly.

I spent a couple of hours this morning installing a new valve cover gasket and O-rings on the injectors. There was a lot of build-up under the valve cover, but I cleaned most of it out and lubed everything with oil from the top. The new O-rings worked well.

I put 5-7 gallons of gas in the tank plus 1/2 can of Seafoam. I put the other 1/2 can in the oil. I fired it up and let it run. That is when I discovered the leak at the back of the engine. It isn't a drip every minute or two. It is a constant fast drip that leaks so much oil that I had to put a pan underneath it.

I just let the truck set and idle for 30 minutes. I would cut it off, let it set for 15 min and then let it idle again for 30-45 minutes. I just wanted to make sure that oil was getting to the critical parts. I will say that the idle and engine response was much improved. There is very little hesitation. The big problem is that darn oil leak at the back of the engine!!!!

After looking for a Comanche for 2 months, finding one in SC with very little rust (and paying too much), hauling back to NC and tinkering with it for 2 weeks.....now the RMS appears to be shot. :fs1:

I found another MJ that appears to be in much better shape (87 4WD that actually runs) and I plan on buying it on Monday. Should I consider the '88 dead and just park it in the pasture for parts? Should I sell it to someone who can change the RMS themselves and wants a MJ for a project? What would you guys do?

Needless to say I really like these trucks, but at some point a person needs to cut their losses on a project and move on. I have about $1800 in the truck now and I can't drive it. :dunce: I will try to post some pics later tonight. Any advice or comments would be appreciated!!

I will say that I learned this lesson.....Never pay too much for a truck that doesn't run!! Never pay more than a near-salvage price!! There is just too much risk involved.

a rear main seal on a 4.0L is a pretty minor problem. i don't see the issue :dunno:

Yeah... RMS seems like a big undertaking, but it really isn't.

Rob L.

...and the seal only costs ~$15

a rear main seal on a 4.0L is a pretty minor problem. i don't see the issue :dunno:

X2

Ok...I feel like a horses @$$!! :dunce: My Haynes and Chilton manuals both say that the transmission needs to be pulled before replacing the RMS. I Googled "Replace jeep rear main seal" and got 1/2 threads with pics. All of them show how to replace it without pulling the trans.

I got a quote from a local mechanic and it was $500 - $700 for the job. It might be possible to do it myself for < $50. I guess it pays to Google!!!

Feel free to send any links to good repair threads. :cheers:

I might even take some pictures as I go!!!

Rear main seals do not last forever. Doesn't matter if the vehicle is driven daily or parked for several years. If the '88 needs a RMS, the '87 will need a RMS ... if not today, then maybe next week. If it's 4.0L, the RMS does not require dropping the transmission, only removing the oil pan.

Ok...I feel like a horses @$$!! :dunce: My Haynes and Chilton manuals both say that the transmission needs to be pulled before replacing the RMS. I Googled "Replace jeep rear main seal" and got 1/2 threads with pics. All of them show how to replace it without pulling the trans.

 

I got a quote from a local mechanic and it was $500 - $700 for the job. It might be possible to do it myself for < $50. I guess it pays to Google!!!

 

Feel free to send any links to good repair threads. :cheers:

 

I might even take some pictures as I go!!!

First off, Chilton manuals are crap.

Second, the 2.5 needs the transmission to be pulled, as the RMS is a one piece, and the flywheel needs to be removed to do it.

The 4.0 can be done by simply dropping the pan. It's a little messy and time consuming, but it's really not that difficult. Just take your time.

Before you start, when you're buying the replacement, get two. It's not hard to destory the new seal during installation.

Rear main seals do not last forever. Doesn't matter if the vehicle is driven daily or parked for several years. If the '88 needs a RMS, the '87 will need a RMS ... if not today, then maybe next week.

:agree:

my XJ didnt leak a drop when i got it,after a few months i noticed a leak and within a few weeks it was severe.

couple links i have found...

http://www.jeepin.com/features/rearmain/

http://gojeep.willyshotrod.com/HowtoRearMain.htm

I will be getting ready to do this in a couple weeks..... also replacing all the emission hoses that cause oil to get into the airbox..

http://jeep.off-road.com/jeep/article/a ... ?id=257985

Total parts= about 72 bucks at napa.

I have a 88 4.0 this will be getting done on..

i wish the 4.0L had a one piece rear main so you could just drop the transmission and put one in it.

it would be a hell of alot better than the ancient half-arsed two-piece seal we've got.

i wish the 4.0L had a one piece rear main so you could just drop the transmission and put one in it.

 

it would be a hell of alot better than the ancient half-arsed two-piece seal we've got.

clearly you've never had a trans crossmember bolt snap off due to rust.

I hate rust. :rant:

Make sure your CCV system isn't plugged up and is operating properly as well, I greatly reduced my RMS leak by fixing it partially and will be fixing it fully after I get the more pressing issues covered (brakes, fuel tank, etc.) I was leaking a quart every 150 miles, now I am leaking a quart every 300 miles or so.

i wish the 4.0L had a one piece rear main so you could just drop the transmission and put one in it.

 

it would be a hell of alot better than the ancient half-arsed two-piece seal we've got.

 

 

clearly you've never had a trans crossmember bolt snap off due to rust.

 

I hate rust. :rant:

Is it possible to remove one without losing a bolt?

I found another MJ that appears to be in much better shape (87 4WD that actually runs) and I plan on buying it on Monday.

This one didn't happen to be New London did it? If it is, I went and looked at it and can tell you about it.

I appreciate all of the advice and comments. I was able to get the oil pan off yesterday. It didn't take long to get the bolts out, but getting the oil pan to release was pretty tough. It has had 22 years to bond. It is going to be tough to get the seal off the pan and bottom of the block. I didn't get the rear main seal out. My wife and kids came home before I got that far.

The oil pick-up screen had some pretty harsh carbon deposits on it. I am going to take some brake clean to the bottom of the engine. I didn't get home today in time for any work, but I am going to buy the oil pan gasket and a couple of rear main seals tomorrow.

Thanks for the links and comments. I really appreciate it.

couple links i have found...

 

http://www.jeepin.com/features/rearmain/

 

http://gojeep.willyshotrod.com/HowtoRearMain.htm

 

I will be getting ready to do this in a couple weeks..... also replacing all the emission hoses that cause oil to get into the airbox..

 

http://jeep.off-road.com/jeep/article/a ... ?id=257985

 

Total parts= about 72 bucks at napa.

 

I have a 88 4.0 this will be getting done on..

I am going to change the emission hoses to make sure the ventilation is working adequately. The big hose was actually cut off and plugged. I am going to take the valve cover off again and clean those ports mentioned in the article. Good advice.

I found another MJ that appears to be in much better shape (87 4WD that actually runs) and I plan on buying it on Monday.

 

This one didn't happen to be New London did it? If it is, I went and looked at it and can tell you about it.

I actually didn't realize that one was for sale in New London. The one I was looking at was in VA. The guy who was suppose to be selling me the 87 Comanche sold it on Friday!!! I thought we had a deal, but he obviously did not.

I checked out your build thread. You did a really good job on your Comanche!!

I am going to take some brake clean to the bottom of the engine.

This, to me, seems like an inherently bad idea. Now, I may be overreacting a bit, but my thought is that if you start spraying the bottom of an open engine with brake clean, some of it may seep its way into rod and main bearings. Brake clean is pretty powerful stuff and it'll remove coatings of oil with ease. The last thing you want to do is start up the engine with no lubrication between any of the bearings. So when you go to replace the RMS and reinstall the last main bearing cap, make sure you coat the bearing very liberally with some oil or engine assembly lube - do not install it dry.

:agree:

May be a good time to replace the rod and main bearings and oil pump while you have the access.

i wish the 4.0L had a one piece rear main so you could just drop the transmission and put one in it.

 

it would be a hell of alot better than the ancient half-arsed two-piece seal we've got.

 

 

clearly you've never had a trans crossmember bolt snap off due to rust.

 

I hate rust. :rant:

 

Is it possible to remove one without losing a bolt?

yeah, to add to that previous statement, i DAMN sure don't wanna work on any northern vehicles. (never seen one break)

Thanks for the advice on the brake cleaner. Spraying it like that probably does not make sense. I am going to try to get that main seal out today and get it replaced.

Question: A new RMS from the dealership is about $25. Has any tried the fluorelastomer RMS? It is suppose to last much longer. Of course it is 2-3x more expensive.

thanks.

the factory rms should last another 150k. how much more life do you need? :dunno:

If you find a groove in the crank, you might want to try the double-lipped rms. :thumbsup:

It took about 5 hours total, but I replaced the RMS. Drained the oil, dropped the pan and removed the RMS. There is no doubt that this was the original RMS. It was brittle and looked very worn. I cleaned the crud from the bottom of the oil pan. The hardest part was scraping the old gasket from the pan and bottom of the engine.

I bought a Felpro RMS and a rubber Felpro oil pan gasket. I replaced the RMS and used sealant to bind the ends of the gasket together. I re-installed the oil pan with new gasket. I waited almost 24 hours and then fired up the truck!!!

Of course....it still leaked. Not as much as before, but it still leaked a lot. A good drip every couple of seconds. I couldn't believe it.

Any thoughts or comments on what I could have done wrong? Could it be something else beside the RMS? It is possible that the sealant I applied to the oil pan gasket was rubbed off while I was aligning the bolt holes, but I can't see this much oil leaking out because of the sealant.

The engine is really running well with the new fuel pump, O-rings on the injectors and a short treatment of seafoam. I let the engine idle (and leak) for about 30 minutes while I cut the grass. I wanted the new oil to circulate and get the engine lubricated. I just caught the drip and let it go.

What would you guys do next?

I think I understand what I did wrong. I was reading an article on a website and it talked about not skinning any of the upper part of the seal during installation. I remember catch the edge of the seal on the lip of the channel when I had it about 1/2 way inserted. I skinned off a small piece of the seal that was about 1/8 - 1/4". I didn't realize what I had done until I read this article and I remembered doing it!!

I guess this was enough to make it leak under pressure. I will pull it again and try to insert a new RMS.

Should I get a new oil pan gasket as well? Would you guys use Felpro or get a RMS at the dealership? Thanks.