Inliners International Forums General Discussion Engines GMC Rear Main Seal

Has anyone found a better type of rear main seal for a 228 GMC engine? A real good friend has a lovingly restored 40 GMC 1/2 ton and the rear main is a rope type seal and it leaks more than he is happy with. He said he checked Patricks and they had nothing available other than the original rope seals. Somebody must have discovered a suitable neoprene chevron rear seal that solves this problem.

He has 2 more of these 1940 1/2 tons and a 1940
1+1/2 ton he is working on. I'm trying to convince him to do one of the p/ups with a hot 302 Jimmy and modern running gear but so far all he does is squint and grunt back at me. Ya gotta love the purists!, they are not easily strayed off their narrow path.

Thanks for any help you Jimmy guys can offer.

I got a real type seal for my 261 from NAPA Auto Parts maybe they have one for GMC s

There is no neoprene or one-piece seal that will work on a stock GMC crank. Maybe with some special machining, such as Beck's (see advertiser page) offers, but it's really not necessary. A properly installed rope seal, on a crank in good condition, will not leak. Possibly the problem is the seal material itself - newer rope seals lack the asbestos which was impregnated in the OEM seals. You can get NOS asbestos seals from Langdon's Stovebolt.

Improper installation could also lead to leakage - the ends must be trimmed carefully and butted together with a touch of sealant. Doing this with the engine in the vehicle is iffy, unless the mechanic has some experience in this area and knows just how much to drop the crank to fish in the new seal and trim it properly. This is becoming something of a lost art these days.

There's nothing inherently wrong with rope seals - they were used on Buick 455 V8s with no problem.

Thanks Jack and everyone. I'll pass the info on about the seal Langdon's has.

According to Bill Fisher's book"Chevrolet GMC & Buick Speed Manual" GMC and Chevy have the same size bearings on rods and mains. So the seal that fits chevy should fit gmc

Mike G., I am in the process of building what you mentioned; I have a '39 GMC 1/2 Ton, stock frame, straight axle with disc brake kit, 302 GMC 6 mildly modified, S-10 5-speed and rearend. The rest is basically stock except it will have air conditioning. I also have a completely stock '40 Chevy 1 1/2 ton my grandfather bought brand new. It only has 21,000 original miles. But I plan to drive the GMC pickup every clear day I can, and the extra power, more reliable brakes and the comfort of AC in these parts will just make it more enjoyable and safer to drive.