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Long Lasting Rear Main Seal

B

Ben824

NAXJA Forum User
Location
Woodstock, GA
I have had my Jeep 11 1/2 years and I am due for my 3rd rear main seal. I know that those odds are not too bad but I would like to replace it and never have to worry about it again.

Is there a good way to replace this thing and keep it from leaking for year and years to come rather than replace it every 5 years or so?
 
(1) IN all of my years around non professional mechanics, I have yet to know of a single person, other than myself, actually following the approved method of the several coatings required in the assembly of the rear main seal components. It, if at all, is actually necessary to not overlook the "devil in the details", lol, as it requires an even coating, and not sloppily accomplished in order to comply. I have always had great results by following THE BOOK, i.e., any book actually, but I prefer the Service Manual in general over the others.., but in this operation all of the books task one to follow this procedure accurately.

Not saying that you have not followed the book, but there are other possible factors that degrade the rear main oil seal's ability to insure a non leaking fix. (2) Bad materials. (3) The use of synthetic oils in the older XJ models can 'slip' past.

I do not know, (yet), if the more modern 4.0 seals fit the older models.., but I imagine they do.., and they might have been improved somewhat in order to achieve a better sealing of the seal. Since those chinese slave laborers have been making XJ's for years.., is it possible that those seals may have flooded the American market, and have a piss-poor quality control in their production. 'Dunno. Someone here might straighten us both out. Rather than obtaining a seal from some after market shop, perhaps this is one item better gotten from an OEM outlet, i.e., a dealership parts counter.
 
Mercedes found a solution to this problem. But they aren't sharing. I saw one of their rear main seals for the 4.0 application and it looks completely different than the typical OEM, Fel Pro or Fel Pro double lip seal. It is a large, maybe 1/4-5/16 inch wide. half round seal. It has slightly raised, angled fins all the way around, that force the oil back into the motor as the crank turns.

I've been trying to get one in the package (with a bar code) or the number, with no luck so far. They are treating it as a trade secret. I've tried everything short of a bribe to get them to sell me one, no luck so far. I'm sure someplace there is a Mercedes TSB about this seal, I've never seen it.
 
8Mud said:
Mercedes found a solution to this problem. But they aren't sharing. I saw one of their rear main seals for the 4.0 application and it looks completely different than the typical OEM, Fel Pro or Fel Pro double lip seal. It is a large, maybe 1/4-5/16 inch wide. half round seal. It has slightly raised, angled fins all the way around, that force the oil back into the motor as the crank turns.

I've been trying to get one in the package (with a bar code) or the number, with no luck so far. They are treating it as a trade secret. I've tried everything short of a bribe to get them to sell me one, no luck so far. I'm sure someplace there is a Mercedes TSB about this seal, I've never seen it.
Click to expand...


Mercedes uses the 4.0? What application? Or is it an aftermarket thing?
 
skyb44 said:
Mercedes uses the 4.0? What application? Or is it an aftermarket thing?
Click to expand...

After Chrysler bought Jeep, Mercedes bought a large piece of Chrysler. For years, Chrysler, Jeep and Mercedes were serviced and sold at the same dealership, at least overseas. When the Renix was first sold in Europe the Renault dealerships sold and serviced them. Now Fiat owns Chrysler.

Best guess is Mercedes had a replacement seal locally (Europe) designed and produced. Where I first saw the seal was an XJ on the lift at a Mercedes truck service center and then again on my 96 XJ. My 96 came from the Mercedes /Chrysler /Jeep Dealerships owners wife. I removed my rear main seal (bottom) when I swapped out the connecting rod bearings. It still looked good and wasn't leaking, so I left it in there and just reassembled, it hasn't leaked yet. I've replaced the filter adaptor "O" rings, two front balancer seals, the valve cover gasket, pinion seal and a couple of sets of exhaust/intake gaskets and the rear main seal still hasn't leaked.

There is a decent replacement seal for the rear main out there someplace, just finding it is the issue. Best guess is it is a resize of a Mercedes patented seal.
 
Last edited:
skyb44 said:
Mercedes uses the 4.0? What application? Or is it an aftermarket thing?
Click to expand...

After Chrysler bought Jeep, Mercedes bought a large piece of Chrysler. For years, Chrysler, Jeep and Mercedes were serviced and sold at the same dealership, at least overseas. When the Renix was first sold in Europe the Renault dealerships sold and serviced them. Now Fiat owns Chrysler.

Best guess is Mercedes had a replacement seal locally (Europe) designed and produced. Where I first saw the seal was an XJ on the lift at a Mercedes truck service center and then again on my 96 XJ. My 96 came from the Mercedes /Chrysler /Jeep Dealerships owners wife. I removed my rear main seal (bottom) when I swapped out the connecting rod bearings. It still looked good and wasn't leaking, so I left it in there and just reassembled, it hasn't leaked yet. I've replaced the filter adaptor "O" rings, two front balancer seals, the valve cover gasket, pinion seal and a couple of sets of exhaust/intake gaskets and the rear main seal still hasn't leaked.
 
I'm currently going on year 6 with my current jeep, I replaced the RMS when I first got it (oh jesus what a job), but it shows no signs of going again.

It's worth noting, you may not actually have an issue with your RMS, but your CCV system may be plugged and pressure is building up and pushing oil out the back of the engine, this is what caused my first failure. The common cause of this, is the hose that goes from the intake manifold rots out and people replace it with heater hose, however when it has to make the turn around back it gets kinked, which plugs it, pressure builds up and then buh-bye RMS.
 
BULLETMAKER: Whew! Did my '79 AMC Model 17 RMS during lunch-time, stock tires, on my back on a concrete floor. Don't really see much difference with the 4.0. What was your hang-up(s), minor, and major? Removing oil pan due to Stock suspension, or is your XJ lifted? Removing RMS, or installing? Inquiring minds want to know, lol.

8MUD: Older 'feller in my area had a going business of repairs/parts covering most of the pre XJ models. I could go up to the counter, and obtain say: a head light switch, some clips for the internal tail gate window components, distributor bushing, alternator regulator, etc., etc., without waiting days for NAPA to order them, etc. However he began to obtain some early XJ parts in an attempt to keep up with the times. He was really torqued about one early XJ with a distributor mounted on the back of the engine, up against the firewall with all sorts of hoses, tubings, wires, etc., that made the rather simple distributor maintenance a night-mare for him. He pointed that all out to me, and asked me how long did I think it would take to really get to it.., he told me it was an hour. Figured I'd avoid that model. Can't remember if it was a V-6, or straight, but at that time.., I was almost certain I would never get an XJ.., LOL.

Anyway, perhaps if you visit, or drive through a small mountain/valley burg with some Jeep shop, someone there might have that small part getting dusty on a back shelf, and just might sell you that coveted RMS you speak of. Then what? Are you implying that you might be able to steer us towards a method of obtaining them?

Seems Ben824 is one who would...
 
Alaskan:

I'm running stock suspension, which made it a bit more harrowing than it had to be. I think it took me about a day on the first one I did, and then a few hours on the second (I helped a buddy with his).

The real trick to it is getting the oilpan with the new seal back into place, without gumming it all up, and making sure you get the oil pump back in place.

I think if I had to do it again, with stock axles/arms I would pull the top arms so I could drop the axle further. One problem with the stock arms is the axle will only drop until the bottom arms bottom out against the hood that covers the mounting point on the axle. This is a job that I would consider dead easy if not for the axle.

Also, when you're trying to get the stock RMS out, it was sticky and gave me issues, what worked well for getting it out was a chopstick.
 
Alaskan89XJ said:
BULLETMAKER: Whew! Did my '79 AMC Model 17 RMS during lunch-time, stock tires, on my back on a concrete floor. Don't really see much difference with the 4.0. What was your hang-up(s), minor, and major? Removing oil pan due to Stock suspension, or is your XJ lifted? Removing RMS, or installing? Inquiring minds want to know, lol.

8MUD: Older 'feller in my area had a going business of repairs/parts covering most of the pre XJ models. I could go up to the counter, and obtain say: a head light switch, some clips for the internal tail gate window components, distributor bushing, alternator regulator, etc., etc., without waiting days for NAPA to order them, etc. However he began to obtain some early XJ parts in an attempt to keep up with the times. He was really torqued about one early XJ with a distributor mounted on the back of the engine, up against the firewall with all sorts of hoses, tubings, wires, etc., that made the rather simple distributor maintenance a night-mare for him. He pointed that all out to me, and asked me how long did I think it would take to really get to it.., he told me it was an hour. Figured I'd avoid that model. Can't remember if it was a V-6, or straight, but at that time.., I was almost certain I would never get an XJ.., LOL.

Anyway, perhaps if you visit, or drive through a small mountain/valley burg with some Jeep shop, someone there might have that small part getting dusty on a back shelf, and just might sell you that coveted RMS you speak of. Then what? Are you implying that you might be able to steer us towards a method of obtaining them?

Seems Ben824 is one who would...
Click to expand...

If I could ever get a part number I'd track it down someways. I figure the more people looking the better the chances of success. All I ever get by the parts places I've looked is a dumb look and/or too hard can't be bothered. The parts place I use now is good, if it exists they will get it for me, all I have to do is supply a part number.

The only real issues I've had replacing the rear main seal is getting the old pan off the early Renix. Some they installed using Asphaltum (or some sort of black Permatex number one). It was really a pain getting the pan off without bending it up too much. The other issue is the chinese puzzle of getting the pan past the oil pickup if you try to do it without removing the pump. I did it once with the LCA's bottomed and the oil pump and pickup in place. I don't know exactly how I did it, I was getting really frustrated, it came off it has to go back on again ;).. The next time I unbolted one of the LCA's and got another inch of clearance.

I cut an 8 inch piece of brazing rod (brass) with a diameter a little smaller than the end of the top main bearing seal and BFH that sucker. They always came out in one piece and without too much trouble. I can see if you were unlucky it could turn into a real pain though.
 
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This reminds me of a buddy of mine tracking down a internal seal in a Mitsubishi Lancer Evolution transfer case. It wasn't publicly available - seal leaked, you bought a transfer case.
What he did was found a catalog from an industrial seals maker, complete with dimensions and part numbers and chemicals it would seal. Went through that book for a *while* but came up with one that was only a fractional millimeter off. Ordered it, installed it - worked like a charm.
I wonder if somewhere in an industrial supply catalog there is a good 4.0 1 piece seal..?
 
8Mud said:
After Chrysler bought Jeep, Mercedes bought a large piece of Chrysler. For years, Chrysler, Jeep and Mercedes were serviced and sold at the same dealership, at least overseas. When the Renix was first sold in Europe the Renault dealerships sold and serviced them. Now Fiat owns Chrysler.

Best guess is Mercedes had a replacement seal locally (Europe) designed and produced. Where I first saw the seal was an XJ on the lift at a Mercedes truck service center and then again on my 96 XJ. My 96 came from the Mercedes /Chrysler /Jeep Dealerships owners wife. I removed my rear main seal (bottom) when I swapped out the connecting rod bearings. It still looked good and wasn't leaking, so I left it in there and just reassembled, it hasn't leaked yet. I've replaced the filter adaptor "O" rings, two front balancer seals, the valve cover gasket, pinion seal and a couple of sets of exhaust/intake gaskets and the rear main seal still hasn't leaked.

There is a decent replacement seal for the rear main out there someplace, just finding it is the issue. Best guess is it is a resize of a Mercedes patented seal.
Click to expand...


interesting... if you manage to find them for sale I'll take one.
 
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