I am at a loss! Rear main seal leak!

[slans31]

I have a 1978 CJ5 with (now a new) AMC 304 engine. When I got the jeep it was fine, then the rear main started leaking and the engine started smoking a little. I was told it was blow by and decided to just go ahead and order a "Proformance" AMC 304 . I have had that installed and guess what? the rear main started leaking again. Proformance was good about it with warranty (even though I had to pay the difference per hour) and it was good for a little bit, meaning about 50 miles and started leaking again. I have a 4 spped Transmission and was going to replace the clutch while the engine was out, but the replacement clutch wouldn't fit on the shaft, another wierd finding. Anyone ever had this? I spoke to Proformance as I had to send the old seal in and they said there was nothing wrong with that seal. I wouldn't think my luck would be that "good" to get a bad motor. It runs smooth and great except the oil leak. Any help would be awesome!

 

[Jawbox]

Do you have blowby? If you take off the oil fill cap, is there pressure coming out through while the motor is running? If so, it might be the PCV?

 

[slans31]

Thanks for the reply Jawbox, but I shouldn't have blow by now I would figure with a new engine and I did replace the PCV. The guy who installed the engine says he is baffled and he is a good mechanic (so far), took me a long time to find one in my area. I just came back in after taking the bottom two screws out of the dust cover and it "looks" like it may be from the front of the oil pan gasket. I believe that is a two piece right? I hope that is it.

The wierd concern I have is that the main shaft from the Transmission may has been replaced because the new clutch center teeth would line up with the old clutch center until about half way around then they started to be spaced different. Don't know if that shaft would have anything to do with it. Oh, well time for a beer. Thanks again!

 

[BusaDave9]

Do you have blowby? If you take off the oil fill cap, is there pressure coming out through while the motor is running? If so, it might be the PCV?

Good point!

I shouldn't have blow by now I would figure with a new engine and I did replace the PCV.

I agree you shouldn't but if you do have excessive pressure in the crankcase it could cause oil leaks. Just to eliminate the possibility check to see if there is pressure coming out the oil cap.

Also are we sure the leak isn't coming from the seal at the Transmission input shaft?

 

[slans31]

Thanks for the info, and I am definitely going to do what Jawbox suggested this afternoon. Also, wouldn’t Transmission fluid be thicker than engine oil? When the engine was out they checked the Transmission and said it was clean but I will have them look again. This Jeep has turned into a real “labor of love” project but and have a lot in it. Funny side not; My wife has expressed some “concerns” about being a bit over budget with the project and we saw an older model jeep for sale and they were asking $18k! So she didn’t feel so bad after that Thanks for the info again!

 

[JR74CJ5]

Also, wouldn’t Transmission fluid be thicker than engine oil?

Yes... But some of them look fairly similar when leaking out of a hot engine / tranny

You could pull the dust boot and possibly peer in the bell housing with a flash light to see the input shaft seal and be sure though...

I need to start tracking down all my leaks too... Always another thing on the to do list isent there...

 

[Greg]

If you find the rear main is what's leaking,you might want to take a look at the tranny input shaft,for straightness, you'll have to pull the motor,or tranny to fix the seal, this would be a good time to put a straight edge on the shaft, unlikely cause but if the tranny has been removed before, it could have been dropped, shaft hitting floor first, also check all around the bellhousing, to make sure it is up tight to the block,a bent allignement pin could be keeping bellhousing from propper alignment.

 

[slans31]

Hey Greg! Thanks for the info! There is something strange with the input shaft anyway becasue two clutch disks that were supposed to fit don't fit. I have heard that some people will replace that shaft and may kind of do a "half job" on it.

I also checked pressure by taking the oil fill cap off and there was no pressure, but avutally a little suction and when I removed the PCV the eingine died so all appears good there and engine pressure is where the book says it should be. Thanks to all of you for the info! This is really helping out!

 

[Busted Knuckles]

Simple solution to your oil leak, is dye. Put florescent dye in your motor oil and then hit your motor with a black light. That will take you to the source of your leak. Your tech should have been on that from go. If the leak is bad, I dump it in the oil and start looking almost immediately, not in a week or two.

The AMC 8s also sit at a pretty good angle, I would not be surprised to learn your leak is up front and dripping off the back of the motor.

 

[JR74CJ5]

The AMC 8s also sit at a pretty good angle, I would not be surprised to learn your leak is up front and dripping off the back of the motor.

^^ Very good suggestion too...

 

[Johnboy]

Jeep tranns 70s era would have a input shaft with 10 splines at a 1 1/16 od i beleive if you have a freind that has a chevy clutch disc try it i know that sounds odd but it may fit. Chevys are 10 spline aswell but different od. on input shaft. Who knows it might fit.

 

[slans31]

Thanks once again for the responses! I already did the dye test when the first seal on the new engine started leaking and it showed from the rear seal. I looked behind the engine and nothing. It is pretty clean! I am thinking now it is between the Transmission and engine. Just found out the type of Transmission I have (T170) so now I know that it is not original and I do think (like suggested above) that the main shaft might be messed up. I really thank you all for the info and will keep everyone posted!

 

[slans31]

Well I have found out it is the thrust bearing. Would anyone know the length of the input shaft for the T170 I have in it now, compared to the one that would have come original? I knw this is pretty vague, but I would like to know as I am being shipped another new engine. Thanks!

 

[bmflyfish]

On the positive side of things at least the company you bought your motor from is standing behind there product.

 

[slans31]

It has been a HUGE fight for a "no hassle warranty", but yes they are standing behind it now. The bad part is I am out of pocket on EVERYTHING up front and they only pay $40 an hour for labor (Autozone policy), I am stuck with the rest.

 

[Turbogus]

If you're confused about engine oil leaks and gear (Transmission ) leaks, your can tell the difference easily ~ by the smell. Gear oil has a definite FUNK to it.

 

[BusaDave9]

If you're confused about engine oil leaks and gear (Transmission ) leaks, your can tell the difference easily ~ by the smell. Gear oil has a definite FUNK to it.

Yes the leaks are hard to tell apart.
Actually, the rear main seal is a common leak and it is uncommon for the Transmission input seal to leak. The reason is the rear main seal is 2 piece. The Transmission input seal is one piece and can compress down onto the Transmission input shaft. In other words its easy to make a tranny seal that doesn't leak but sealing the rear main is an issue.

Where does the oil level go down? engine? tranny?

 

[gert]

Something that I have had a problem with old cranks and vibration dampers are the seals wearing a groove in them once this groove is there it will always leak. That could also be your problem

 

[Turbogus]

Hey Dave, not callling ya out or anything but in my experience the two leaks are not difficult to tell apart (engine oil and Transmission 90wt gear oil). If there's any doubt one can always check at a Transmission . or auto shop and ask if you can have a whiff of gear oil~there's no mistaking that FUNK, honest

....and in the case of an automatic Transmission . isn't the ATF red in color?

 

[jasonmark1993]

Might want to put a little research into the proper length of the input shaft with XX bellhousing, block plate, etc.

Might be pushing on the crank and ate the thrust bearing.