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Discussion Starter · #1 ·
I have a 383 that has a rear main seal leak, I replaced it with a 350 rear main seal and it still leaks :spank: Ive done some research and found out that there is a rear main seal for a 350 and a rear main seal for a 400, my question is , do i need a 400 rear main seal due to the 400 aftermarket crank or do i need a 350 rear main seal due to the 350 case, hopefully it a 400 seal, at least that will explain why i still have the leak.......I guess,
 

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If it`s a 2 piece seal this a common leak area which was why Chevy went to a 1 piece design in 1986. If the block is a factory 350 then it takes a 350 seal. The 350`s main bearing size is 2.450, a 400`s is 2.650. The 400 shaft`s main bearings are ground down to fit the 350`s main bearing saddles. In your case of a aftermarket crank it was made with 2.450 journals.
 

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The seal will only work in the correct orientation. If it's backwards, it'll leak. If it was installed bone dry, it might have been damaged enough to leak.

If it was installed w/the crank in the engine, that can cause grief as well- from dirt or old seal material staying in the hard-to clean upper seal groove, damaging the seal material while installing the upper half, deforming the lower seal half by taking up the rear main cap bolts before the other caps have brought the crank back into position, etc.

You prob. are already sure, but check to see that it's not the pan to rear main cap seal.
 

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Discussion Starter · #4 ·
Thanks again guys , you always come through when i get stuck, i couldnt be more appreciative to the small community of frendly and and helpful folks on this site, But one last question, I do have a 2 peice rear main seal , is it possible to use a one piece seal, or do they make a one piece seal for the older cases?
 

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alle4901 said:
but if a 1 peice is better for preventing leakage the why would they make a 1 peice convert to a 2 piece?
So people (racers) can use the $1000 2-piece rar main seal race crank they already have in a one piece rear main seal block and not have to buy a new crank.
 
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