The Stovebolt Site Forums The Shop Area Engine Shop Rear Oil Seal

I just completed a head rebuild on my truck and thought while I was at it I would fix the oil pan. Everything went back together fine but when I drove the truck it was leaking from the tranny cover. I assume this is the rear main seal. It's a 1950 3/4 ton with a '49 235. After shutting it down, it leaked about a 8" diameter puddle. After reviewing the postings on the forum, it appears as though this engine is prone to leaking. Should I attempt the fix or is it just going to leak again?

Keep in mind that I bought it not running so this is the first time I have had it running and therefore don't know if it leaked before.

It sounds to me that this is not a leak that you would want to live with. Can you get a small mirror to look at the back of the head to make sure it is not coming from the valve cover ? The old rear main seals commonly seep a little, but not a puddle like that. If that were coming from the rear main, it would trash your clutch in no time.

Since you've worked on the cylinder head, check out the valve cover first. Chances are, you've got a leak there, which is running around the bellhousing and dripping off the bottom. Always remember, oil can't run uphill, so look for the highest wet spot.
Jerry

Great advice guys. I did put a new valve cover gasket on it and just assumed it was fine. When I looked at the tranny cover, it was leaking out the whole in the very bottom. I'm pretty sure it is coming from within the cover but I'll look tonight. Also, this engine was rebuild a few years ago and probably only has a few hundred miles on it. I don't know what kind of seal they used as a replacement.

Well, I checked the valve cover gasket and it is wet. I also felt the new gasket on the front and back edge and the cover isn't tightening down on the gasket. Regardless of how tight I get the valve cover, the gasket moves in the front and back. I am hopeful this will fix the oil leak once I figure out how to get it sealed.

Any tips on sealing the valve cover? I didn't use adhesive because I wanted to be able to adjust the valves in the future.

The first time I did this I glued the gasket to the valve cover with Indian Head shellac. That didn't work. The next time I glued it to the head, better, but still leaked at the front and back. Spent some time flattening the flange at the front and back on the valve cover, and then put a small bead of hylomar just on the front and back flange of the cover. I don't like to use this stuff with cork gaskets, but it did seem to stop the leak. hopefully when I take off the valve cover again, it will scrape right off!

I just resealed my valve cover with Permatex #2. For the most part it sealed. I have a little bit of seapage at the back of the valve cover AND still the same drip on the ground.

The leak at the valve cover is minimal. I really don't think it's enough to cause this much on the ground. The funny thing about it is that I can let the truck idle and it doesn't drip. I thought this was a good indication it was not the rear seal.

However, if I drive it and then bring it back in the garage and let it sit for 1/2 hours or so, I get a spot on the floor about 6" in diameter.

I'm going to seal the valve cover AGAIN but I don't believe it could all be coming from this spot.

If it was a rear main, wouldn't it leak any time it's running??

Any ideas?

I just finished replacing my rear main seal, oil pan gasket, timing cover gasket and seal, side cover gasket & valve cover gasket. I'm too chicken to turn the engine over. Hopefully I won't be chasing too many puddles.

When the rear main leaks, the oil gets slung around by the flywheel and sprays all over the inside of the bellhousing. After the truck sits awhile, this oil slides down into the inspection cover and leaks out the weep hole. This is why it doesn't show up as a puddle on the ground right away.

That's interesting because I don't see a lot of oil on the flywheel, if any. There is some on the bell housing and crank cap. Other than that, I don't see much.

Even if it was being slung around, it should leak while running. It has to go somewhere, correct?

Start with a couple of spray cans of degreaser like Gunk, and get the inside of the bellhousing as clean as possible, ditto around the back of the engine and valve cover. Hose it off with hot water if possible. Once it's clean, it's much easier to spot the location of a leak. I used to use a product that turned the oil bright red, and it was easy to see what was newly-leaked oil, and what was residue from previous leaks. It's been over 20 years since I used it, and I don't remember the brand name or manufacturer.
Jerry