1978 CJ5 w/304 has bad rear main seal leak, we need experts

1978 CJ5 w/304 has bad rear main seal leak, we need experts


Tallahassee, FL
1978 Jeep CJ5 Levis edition with a 304 stock engine
Hi my name is Kelly. I have been reading these boards for years. Now I need some help.

I have a 1978 CJ5 with a 304 engine and she has a horrible rear main seal leak. I have a mechanic that has been doing most of the work to her, we trade out labor for hunting.

My mechanic is at his last wits end regarding the RMS. Below is a basic summary of what he has done.

"Rear main seal has been replaced four times I have tried all aftermarket brands of seal I have also measured and special ordered my own seal and to no avail still leaks. I replaced the main bearings because the rear bearing was a bit scarred, no groove or marks noticeable on the crank. No apparent damage to rear main cap. Checked Pcv system operation, pulled trans back to inspect cam plug on end of block, checked for oil leaks on top rear of engine."

When this leak started it was only minor, as he has tried to fix her, she leaks bad when you first start the jeep as she warms up then she would stop. Now she has gotten to the point where she leaks a quart of oil in 150 miles.

This is my everyday driver, the 304 only has 42k miles on it. The jeep was a farm vehicle for many years, drivin very little. She is in great shape just 30 years of wear catching up to her.

My mechanic and I need help figuring out this oil leak from the rear main seal.
Well, sounds like you guys have checked a lot of the right things.

Im assuming we are 100% positive this is a rear main leak and you used dye and a uv light. Ive seen a lot of guys get burned, most of all myself, by going after the rear main. Its real easy to have oil from the pan, head, or intake there.

Double check the part number of the seal vs your application. You can also try a different brand.
I went through this with the 360 in my old CJ5. I had the pan off and on 3 times for that rear main seal till a friend of mine gave me a tip.

Along with the above mentioned seal put a small dab of permatex on each one of the "feet" of the seal itself. That was the last time I had to drop the pan for that leak.
Hey Jason, we used the uv dye and watched it drip out of the top of the 2 piece seal.

Thanks for all the tips on the type of seals...get this little fun fact. The last seal we tried was a custom measured and made, bought from a place in Valdosta GA. It was actually longer than the AMC seal, and two other brand seals we tried prior. We did this because an old school mechanic said some of the 304s were larger???? It worked for 1 day, then started leaking.

Pete, I know he uses alot of Right stuff sealer, I will pass on that info, thanks.

Hey CJ, glad to know your close by. I actually drive Levi Edition from Tallahassee to Americus, GA via Old Albany Rd 3 at least once a month during hunting season. She has left me on the side of the road outside of Americus once when the timing went out, that was an expensive tow. Now I am fighting a fuel pick up problem during these 120 mile one way trips, but that is another topic.

I am trying to find as many "little things" as I can, I think I leaked a quart just on the trip home today from the hunt camp.
dang man thats brutal having to redo that job over and over.

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