Rear main seal advice please.

[bobby dee]

Hi there, semi-newbie (and oldbie at the same time!)

Very long story short, I replaced the 350 in my 75 C2500 with a "rebuilt" 350 (circa 1972). (first engine swap) Got everything running again, (not too bad, and learned a lot and asked a mazillion questions) and running nice.

Except.

Oil leak at the rear main seal (positively identified from much ttesting)

Anyway I am proceeding with the seal switch. According to all information I can find, it is a two piece and should not be as much trouble as pulling the engine was.

Any words of wisdom from anybody out there would be great.

Thanks

 

[tRustyK5]

The seal replacement isn't hard, it's getting to it. Trans needs to be unbolted and moved back at the very least. Oil pan dropped. With the two piece you need to make a tool from a wooden dowel to be able to push the upper half into it's home. I try to skew where the seal halfs meet so they aren't perfectly aligned with the rear main cap. I put a small dab of RTV on the ends of the seal halfs, and a super thin skim of RTV from the seal out to the pan gasket and then torque the rear main cap before that sets. I also skim a thin coat of moly grease on the seals themselves before installing them.

I've had good success doing it like that...

 

[diesel4me]

I did two rear main seals,one on a straight six in a '75 2wd Blazer,and another in a 350 in my '72 K5..neither one did I touch the transmission, other than pull off the tin shield under the TH350 on the '72,the other truck had a Saginaw 4 speed..

I was able to get the oil pan off both trucks fairly easy,I did have to take out one motor mount thru bolt on the straight six 2wd truck and lift up the engine an inch or so to get it past the crossmember--the 4x4 '72 was duck soup,nothing in the way other than tranny cooler lines,once I jacked up the truck by the frame and let the front axle hang down..

I took off the rear main bearing cap on both after marking its position,and used a "chinese finger" tool to install the upper half of the rear main seal ,and put some RTV at the corners where the oil pan meets the bearing cap--I also replaced the rear main bearing,as it had some copper showing on both engines--they never knocked or rattled on cold starts,but I wanted no "slop" in the rear main bearing,that might have contributed to making it fail and leak..

I lost half of one front tooth when a socket fell off an extension while lying on my back under the '75 2wd Blazer,and it made a direct hit--split my upper lip too...only injury I got besides some bloody knuckles..I was glad neither one ever leaked there again when the job was over..

 

[bobby dee]

And what are the chances I can re-use the brand new oil pan gasket that I just installed?

 

[diesel4me]

If it is the one piece type you should be able to re-use it provided it wasn't damaged anywhere...might want to smear some 3m weatherstrip adhesive on it to help it stick to the block while you put the pan back up..