C3 Small block rear main leak

[Rick M.]

I have put 2 rear main seals and it sill leaks? Any suggestions. Thanks

[Mike F.]

Re: C3 Small block rear main leak

Short of an engine rebuild, (which only delays future leaks) it's a losing battle.

[Patrick H.]

Re: C3 Small block rear main leak

Are you sure it's the rear main seal that is leaking?
The front of your Muncie can leak and it looks virtually the same from below.

[Dick W.]

Re: C3 Small block rear main leak

Are you using sealant on the ends of the seals? They can leak there. Another question, is the crankshaft grooved? If so, there ain't nothing you can do while it is in the car to stop the leak.

[Rick M.]

Re: C3 Small block rear main leak

I'll check the trans. And yes I used sealant and no grooves. Thanks for the replys.

[Patrick H.]

Re: C3 Small block rear main leak

I've been tempted to get some of the leak detector fluid that you can add to oil or trans fluid, and look with a black light.
I've been fighting the same type of leak and highly suspect the trans myself.

[Timothy B.]

Re: C3 Small block rear main leak

Rick,

Also, to add to Patrick's post check things like the valve covers for a leak at the lowest point because this leak can run down and drip at the lowest point and appear like a rear seal. I have a terrible time keeping me steel valve covers from leaking on my 300hp cars.

[Dick W.]

Re: C3 Small block rear main leak

Another comment to this thread, I learned a long time ago that the only Chevy engine that does not leak oil, has no oil in it.

[Erv M.]

Re: C3 Small block rear main leak

This may be helpful

Rear Main Seal

Just read an interesting article in the current Corvette Restorer by John Bissell regarding the two different rear main seals available for the SBC - Fel-Pro parts #2900 (silicone, blue) and #2912 (fluoroelastomer, red), wherein the author espouses the superiority of the red #2912. Basically the #2900 is old technology and the new #2912 does the job.

[Jim D.]

Re: C3 Small block rear main leak

This may be helpful

Rear Main Seal

Just read an interesting article in the current Corvette Restorer by John Bissell regarding the two different rear main seals available for the SBC - Fel-Pro parts #2900 (silicone, blue) and #2912 (fluoroelastomer, red), wherein the author espouses the superiority of the red #2912. Basically the #2900 is old technology and the new #2912 does the job.

The #2900 will work fine IF it's installed correctly. I've been using that one for decades and have never had one leak yet. You MUST off-set the seal ends and use a dab of sealer regardless of which seal you use.

[Joe L.]

Re: C3 Small block rear main leak

I'll check the trans. And yes I used sealant and no grooves. Thanks for the replys.

Rick-----

In 1986 GM redesigned the small block to use a 1 piece seal. This involved significant changes and undoubtedly cost GM a lot of money. You don't suppose they did this because the 2 piece design worked just as well, do you?

[Joe L.]

Re: C3 Small block rear main leak

This may be helpful

Rear Main Seal

Just read an interesting article in the current Corvette Restorer by John Bissell regarding the two different rear main seals available for the SBC - Fel-Pro parts #2900 (silicone, blue) and #2912 (fluoroelastomer, red), wherein the author espouses the superiority of the red #2912. Basically the #2900 is old technology and the new #2912 does the job.

Erv-----


The only seal which GM has had available for 2 piece seal small blocks for the last 20 years is the fluroelastomer type. GM #10243247, same as Fel-Pro 2912. The 10243247 is now discontinued but the Fel-Pro 2912 is still available.

[Jim D.]

Re: C3 Small block rear main leak

Rick-----

In 1986 GM redesigned the small block to use a 1 piece seal. This involved significant changes and undoubtedly cost GM a lot of money. You don't suppose they did this because the 2 piece design worked just as well, do you?

Why they did it? I don't know as they successfully used the 2 piece seal for 20+ years. The 1 piece certainly isn't leak proof. My 93 had the rear main seal replaced under warranty twice and they never got it to stop leaking. I sold the truck. That stopped it. There's many 1 piece leakers out there. Like I stated earlier, installed correctly, a 2 piece won't leak.

[Gene M.]

Re: C3 Small block rear main leak

Rick,

Also, to add to Patrick's post check things like the valve covers for a leak at the lowest point because this leak can run down and drip at the lowest point and appear like a rear seal. I have a terrible time keeping me steel valve covers from leaking on my 300hp cars.

Good advice here, most times it is the valve covers and not the rear main seal..............
For a driver I suggest the finned aluminum covers for leak free driving.