oil leak between bell. and trans

[Jack O.]

Hi,

I just replaced my oil pan gasket and rear main seal. Everything looks good there but I still get oil creeping down between the trans and bellhousing. It also seeps out from the bottom of the bellhousing between the bellhousing and the cover. From what I can see the rear of the pan and seal are dry. My first thought was gear oil but it doesn't have that nasty gear oil smell and doesn't seem as thick as gear oil. I also replaced the trans oil to be sure it wasn't over-filled and therefore know it has the proper gear oil in it. It only leaks when its been running. I'm not sure since I haven't ran it very long, but it seems to start dripping after I have shut off the engine. Any clues?

Thanks.

[Mike M.]

Re: oil leak between bell. and trans

what year vet, what engine, what trany? mike

[Dennis C.]

Re: oil leak between bell. and trans

Just to make sure - double check the back of the intake manifold to confirm you don't have any engine oil escaping by that route.

[Joe L.]

Re: oil leak between bell. and trans

Jack-----

What you describe sounds like a rear main seal leak. In fact, it's almost classical in its symptoms. Primarily, my comments are going to be based upon the assumption that we're talking about a 59-86 engine with 2 piece neoprene seal.

1) Did you apply sealant to the areas adjacent to the seal shown in the Chevrolet Chassis Service Manual? If you didn't, this IS the cause of your problem. You might just as well go back in now and do it;

2) Did you check the crankshaft journal where the seal rides to see if there was ANY scoring or grooving? ANY scoring or grooving of this journal WILL result in an in-service oil leak;

3) Were you extremely careful to avoid damaging the seal halves, front or rear, when you installed them? ANY damage to the seal will result in an in-service leak.

Another possibility, but a much less likely one, is an oil pan leak:

1) Did you use silicone sealer at the interface between the side gaskets and the rubber end seals? This is very important for a good seal. If you used a 1-piece oil pan gasket, which in my opinion is the only way to go, you don't need to be so concerned with this. In fact, if you used a 1-piece gasket and installed it properly, you can just about rule out an oil pan leak.

[Mike M.]

Re: oil leak between bell. and trans

if your small block engine is a pre-59 case that utilized the old rope type rear main seal, you can remove it and replace it with a neoprene seal. it you need source, let me know and I'll get you Gary Pronesti's phone #. they sell for about 15.00

[Craig S.]

Re: oil leak between bell. and trans

Anohter possible leak point are the two lifter galley pipe plugs in the back of the block...I once had an apparent rear main leak tur out to be a weeping plug there....finally discovered the problem upon removal of the engine for rebuild, and had gone throug a couple main seal replacments first....all oil flows down to the same basic place...Craig

[Dennis C.]

Re: oil leak between bell. and trans

Joe - Would you please supply source and P/N for the 1 piece pan gasket. Thanks, Dennis

[Craig S.]

Re: oil leak between bell. and trans

Dennis - here they are, Felpro OS34509T for 57-74 SB chevy, Felpro o334510T for 75-85 SBC. Summit has them for $33 and $34 each respectively...Craig

[Craig S.]

Re: oil leak between bell. and trans

Dennis - here they are, Felpro OS34509T for 57-74 SB chevy, Felpro o334510T for 75-85 SBC. Summit has them for $33 and $34 each respectively...Craig

[Craig S.]

And the one piece BBC is...

Fel-Pro OS-30061T ....Craig

[Joe L.]

Re: oil leak between bell. and trans

Dennis----

The Fel_pro part numbers and applications that Craig provided are correct. However, there is one other thing to consider. If one has a 56-74 Corvette with a GM replacement oil pan purchased after about 1975, then the 75-79 1 piece gasket, OS-34510T must be used. That's because these replacement oil pans had the larger front seal radius of the 75+ small block pans. The REPLACEMENT pans included in this are:

1956-GM #360867

1957-62---GM #359937

1963-74 "5 quart"---GM #360866

1963-72 "6 quart"---GM #359942

The above-referenced pans have an oil pan front seal radius, measured from the bottom of a straight edge placed across the oil pan rails to the center of the seal radius, of 2-3/8". Original 63-74 oil pans have a dimension of 2-1/4".

[Dennis C.]

Re: oil leak between bell. and trans

Many thanks to all involved in helping. I have never seen one of these 1 piece gaskets, let alone used one. DC

[Patrick H.]

Re: oil leak between bell. and trans

Dennis,

They work extremely well. I installed on in my 71 a year ago and was impressed at how easy it was to install, and how well engineered it was. I just wish I could get one for my 1970 Cutlass.

By the way, if you ever use one be sure to verify that your oil pan rails are straight, with no deformed bolt holes due to overtightening.

Patrick

[Joe L.]

Re: oil leak between bell. and trans

Dennis-----

The 1 piece oil pan gaskets are the ONLY way to go, judging considerations aside. Chevrolet went to the 1 piece configuration in 1986 for small block engines with the then-new 1 piece real main seal configuration (oil pans are different for 1 piece rear main seal blocks than for 2 piece rear main seal blocks). However, GM never offered a one piece oil pan gasket for pre-86 small blocks with 2 piece rear main seals and originally fitted with 4 piece oil pan gasket sets.

Fel-Pro does offer such gaskets, though, and they're a "sweet piece". It solves a lot of oil pan leak problems and it's much easier to install than the 4 piece sets. No sealer required, either. A real clean installation, to be sure.

You can't convert a 2 piece rear main seal block to a 1 piece (but you can convert a 1-piece rear main seal block to a 2 piece seal with an adapter available from Chevrolet). Properly installed, a 2 piece seal will seal just about as well as a 1 piece. Plus, you don't have to remove the transmission to replace the 2 piece rear main seal as you do to replace the 1-piece style.

[Dennis C.]

Re: oil leak between bell. and trans

Thank you, thank you, thank you. Dennis