The rear main seal on My M38A1 was leaking

Deadguy · Post by **Deadguy** » Wed Jan 16, 2013 12:54 am

So I replaced it, and with an NOS one, not one of the cheap Chinese jobs. My cuno oil filter was leaking, so I pulled, cleaned, reinstalled, and used gasket sealant. The engine had lost some oil, so I filled it back up, and may have put a little too much in (but just a little). The rear bell housing started to leak some oil, and I was thinking that the new rear main oil seal was bad. I cleaned the clutch/bell housing up with brake cleaner (through the hole on the bottom, I didn't remove the whole thing. The oil leak hasn't reappeared, and a check of the engine oil shows it is fine. Is there a "weep hole" or something back there, to drain excess oil?

Post by **wesk** » Wed Jan 16, 2013 1:33 am

There are generally only a few good reasons for oil to drip from the bell housing. First make sure which oil it is. Gear oil from the tranny or engine oil from the engine. Or if you are one of the way up north guys that uses engine oil in both then it will be tougher to pinpoint the leak.

Leak sources are:

1-Rear main seal.
2-Oil pan gasket
3-Rear cam journal welsh plug
4-Tranny input shaft seal.

There are no openings there that are meant to allow oil to weep.

There are plenty of discussions you can review on the wisdom or lack of in using certain rear main seals. Ancient NOS stuff is not a good choice.

Deadguy · Post by **Deadguy** » Wed Jan 16, 2013 2:36 am

It was definitely engine oil. John from Midwest said he couldn't get any good ones, just cheap one's from China. I bought a seal off Ebay, and whether it was NOS or not, I don't recall, he was saying it was the correct, American made version, not the Chinese imitations.
What is the "Rear cam journal welsh plug "? And, like I said, it stopped. I then sprayed brake cleaner in there, and it hasn't come back.

Post by **wesk** » Wed Jan 16, 2013 10:20 am

When not so bright folks install the cam gear on the front of the cam they ignore the warning "Do not hammer on" and when they hammer it on the cam bounces against that rear journal plug and loosens it and out comes the oil.

Deadguy · Post by **Deadguy** » Thu Jan 17, 2013 3:35 am

Hmm, I guess there's no way to check without pulling the whole thing, is there? With my Overdrive, PTO, Transfer Case, Transmission, and Clutch, that takes all day.

Post by **wesk** » Thu Jan 17, 2013 10:34 am

I have warned folks complaining of rear seal leaks for at least 20 years to make sure the real leak is not that plug before they change the rear seal.
You can imagine the frustration of installing one or even two new rear seals and have the leak remain and then finally get smart and pull the engine so you can inspect the rear of the block and find that welsh plug loose! This is another reason I always suggest pulling the engine for a rear seal leak. It has many benefits.

1-You get a much better look at the back of the engine.
2-You get an opportunity to inspect the condition of the clutch, pressure plate,
throwout bearing and pilot bushing.
3-You don't have to work laying on your back under the jeep.
4-The seal is easier to change with the crank raised up or removed while the engine is inverted on the engine stand. This results in much higher first time seal replacement success rate.

The engine can be pulled in 45 minutes and re-installed in a hour and a half.

Deadguy · Post by **Deadguy** » Fri Jan 18, 2013 11:15 pm

Any theories on why it was leaking oil, and then suddenly stopped?

Post by **wesk** » Fri Jan 18, 2013 11:36 pm

Do you have fording valves on it? If you leave them in the fording position it will push oil out.

Deadguy · Post by **Deadguy** » Sat Jan 19, 2013 12:48 am

Where would they be, and how could I tell?

Post by **wesk** » Sat Jan 19, 2013 9:45 am

Just review the Fording system information in your M38A1 service manuals.

Deadguy · Post by **Deadguy** » Sat Jan 19, 2013 11:24 am

I'm looking, and I just see that valve, activated by the fording cable on the dashboard. It was sticking (but in the off position), and I cleaned it up a few days ago.

Post by **wesk** » Sat Jan 19, 2013 11:46 am

There are two valves in the system. One on the cross over pipe and one on the left side valve cover adjacent to the PCV valve.

Deadguy · Post by **Deadguy** » Mon Jan 21, 2013 3:51 pm

I double checked, tightened, and adjusted both fording levers and cables. Both were kind of wonky beforehand (sticking in place, but more open than closed). The oil "leak" hasn't come back, and I topped off the engine oil. Do you think I'm ok for now Wes?

Post by **wesk** » Mon Jan 21, 2013 6:58 pm

You should be. Wait and see.

Deadguy · Post by **Deadguy** » Thu Jan 24, 2013 12:57 pm

So Wes, I took the vehicle for a long ride, 2 1/2 hours both ways, and when I pulled back into my garage, I looked at the bellhousing, and noticed there was an oil leak. It's pretty minor, and I was driving at speeds of up to 66 mph, for a total of 5 hours straight. I checked the engine oil level, and it's fine. What do you think?