SBC 400 Rear main Vs Rear Oil Pan Seal - Hot Rod Forum : Hotrodders Bulletin Board
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Old 02-11-2010, 05:58 PM
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SBC 400 Rear main Vs Rear Oil Pan Seal

With all the Knowledge out there , will someone please educate me or give me a crash course or Engines 101, in determining if my "Rear Main Seal" is lkg or is it my "Rear Oil Pan Seal" on a SBC 400? I currently have a leak between my manual Tranny (Muncie) and the rear of the oil pan. Not a Humungous leak but a leak either way. Just don't know what it may be. Grew up Old school always hearing, "Yeah, Rear Main Is Leaking"? How can you tell? Thanks in advance.

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Old 02-11-2010, 06:15 PM
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its the rear main seal. The two piece rubber seal that goes around the crank. SBCs have always leaked there. So my bets are its the rear main seal. Not too much oil is seen at the pan level besides whats splashed off the crank.
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Old 02-11-2010, 06:37 PM
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afsog, it could be either of them, you just have to look..... "SBCs have always leaked there" ???? I've had a bunch of SBC and never had a rear main leak, guess I've been lucky!!
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Old 02-11-2010, 06:42 PM
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Originally Posted by 327NUT
"SBCs have always leaked there" ???? I've had a bunch of SBC and never had a rear main leak, guess I've been lucky!!
Why did gm switch to the 360 degree one piece rear main seal in 87 then? Maybe I should have said "leak prone."

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Old 02-11-2010, 06:52 PM
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Rear Main Vs Rear Oil Pan Seal

I failed to mention this engine has approximetely 100 miles at most and has been Dyno'd. Built professionally by a Well Known Racing Shop in San Diego. Engine sat on Engine stand for approximetely 3 years prior to initial startup. Could seals have dried out? Engine did have oil during it's idle period. Upon installation, Valve covers were pulled and oil was found on top portion of heads. Thanks to all.
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Old 02-11-2010, 07:03 PM
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Yes, "leak prone" I like that better. And yes all the gaskets and seals due to just sitting could be very "leak prone"
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Old 02-11-2010, 07:18 PM
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Quote:
Originally Posted by zildjian4life218
Why did gm switch to the 360 degree one piece rear main seal in 87 then? Maybe I should have said "leak prone."
They actually switched due to government regulations on the "carbon footprint" of a car. Feds were looking at fluid drips x "xxx" million vehicles and the impact it has on the enviroment. This combined with the manufacturers push to offer longer warrantees were the reasons bottom end (and entire engine)sealing was revamped.
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Old 02-11-2010, 07:21 PM
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Quote:
Originally Posted by ericnova72
They actually switched due to government regulations on the "carbon footprint" of a car. Feds were looking at fluid drips x "xxx" million vehicles and the impact it has on the enviroment. This combined with the manufacturers push to offer longer warrantees were the reasons bottom end (and entire engine)sealing was revamped.
lol nice. Learn something new everyday
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Old 02-11-2010, 10:37 PM
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Quote:
Originally Posted by ericnova72
They actually switched due to government regulations on the "carbon footprint" of a car. Feds were looking at fluid drips x "xxx" million vehicles and the impact it has on the enviroment. This combined with the manufacturers push to offer longer warrantees were the reasons bottom end (and entire engine)sealing was revamped.
Hmmm. seems like I have had just as many front seals leak as rear 2pc. and with the front being a 360 since inception--------something to ponder; I think seals work fine until they wear enough off the crank surface to allow a leak. New seals on a new crank work fine; new seals on old crank many times will leak almost immediately.
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Old 02-12-2010, 06:08 AM
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A trick I've used a time or two on troublesome 2 piece seals is to sand the ends of both seals a bit, lay a thin shim (like .010"?) in the block and the main cap, to shim the seal inward, and use a dab of RTV (or better yet, now there is Right Stuff) on the ends of they seal halves where they meet, along with a little RTV smeared on the OD of the seal. Might sound a little cobbled up, but it cured a seal that still leaked after having been replaced twice.
I've cured a bunch of timing cover lip seal leaks with brakleen and some Right Stuff. Clean the whole area up surgically clean with brakleen, then shoot, or smear the Right Stuff in the gap, (as if you were packing a wheel bearing, no air gaps), finish by making a nice smooth "smile" on the joint between the cover and the pan. It WORKS,

Last edited by Rickracer; 02-13-2010 at 09:05 AM.
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Old 02-12-2010, 06:37 AM
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Could be either - if your bellhousing has any type of inspection panel remove that, try to clean the best that you can between the flywheel and back of block and while running try to observe where the leak is coming from (always observe all safety precautions working under a car). You also have potential leak points above those two areas so rule them out as well.

I had one rear main last season that started leaking after 3 weeks of sitting idle - one good hot lap session and it sealed back up, surprised me.
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Old 02-12-2010, 06:40 AM
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Quote:
Originally Posted by Rickracer
A trick I've used a time or two on troublesome 2 piece seals is to sand the ends of both seals a bit, lay a thin shim (like .010"?) in the block and the main cap, to shim the seal inward, and use a dab of RTV (or better yet, now there is Right Stuff) on the ends of they seal halves where they meet, along with a little RTV smeared on the OD of the seal. Might sound a little cobbled up, but it cured a seal that still leaked after having been replaced twice.
I've cured a bunch of timing cover lip seal leaks with brakleen and some Right Stuff. Clean the whole area up surgically clean with brakleen, then smear the Right Stuff in the gap, (as if you were packing a wheel bearing, no air gaps), finish by making a nice smooth "smile" on the joint between the cover and the pan. It WORKS,
I had to do that on the dyno..Had an LA 360 pan on a newer Magnum and the rear cap and timing cover are very slightly different shape on the sealing surfaces. On assembly I trimmed a '99 Magnum one piece pan gasket to fit the rear pan lip where it seals up. Added a little Right Stuff. My first build of a Magnum block so didn't think about the front matching up. At the corners up front there was a step opening up that's not there on the factory magnum pan. Just brake cleaned it off well and shoved the Right Stuff nozzle in a bit and filled each hole on either side. Let it sit overnight since we were done that day. Came back in next day, made some pulls with no leaks.
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Old 02-12-2010, 04:56 PM
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Rear Main Vs Rear Oil Pan Seal

Thanks for the info. Learned a bunch. "On my way to get some RIGHT STUFF"!!
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