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Flexplate Dust Shield/ flywheel cover

There are 3 different versions that I'm aware of.

TH350, TH400 , and 700R4 all share the same bolt pattern but there is a 2-piece rear main seal and 1-piece rear main seal versions. 4L80E by itself.

2-piece rear main seal has a single step in the area to clear the crank output. p/n 14036187
20260301_155247.jpg20260301_155250.jpg20260301_155300.jpg

1-piece rear main seal has two steps. I did not find a part number.
20260301_155212.jpg20260301_155214.jpg
 
I believe the 1-piece rear main seal version is identical to the 2-piece version other than the clearance to the crank for larger and would make it backwards compatible.
 
Really great input, how would I decipher which one would work for me?
It appears it's just a difference in (notches) on the left (passenger side), is that correct?
 
Do you have a 1 or 2 piece rear main seal on your motor? If you are unsure, the later 1-piece rear main seal version (two step notch) would work either way as long as the cover is not for the 4L80E.
 
kennyw said:
There are 3 different versions that I'm aware of.

TH350, TH400 , and 700R4 all share the same bolt pattern but there is a 2-piece rear main seal and 1-piece rear main seal versions. 4L80E by itself.

2-piece rear main seal has a single step in the area to clear the crank output. p/n 14036187
View attachment 523007View attachment 523008View attachment 523009

1-piece rear main seal has two steps. I did not find a part number.
View attachment 523005View attachment 523006
Click to expand...
Do you think a few minutes with a cutoff wheel could turn a 2 piece rear main version into a 1 piece rear main version? Might open up the availability a little bit for the one piece rear main motors with this part likely being factory 1987-1990ish only.
 
EvilGenius said:
Do you think a few minutes with a cutoff wheel could turn a 2 piece rear main version into a 1 piece rear main version? Might open up the availability a little bit for the one piece rear main motors with this part likely being factory 1987-1990ish only.
Click to expand...
Most likely, that is possible and similar to what GM did to modify the casting mold when they changed the crank output.
 
kennyw said:
Do you have a 1 or 2 piece rear main seal on your motor? If you are unsure, the later 1-piece rear main seal version (two step notch) would work either way as long as the cover is not for the 4L80E.
Click to expand...
Unfortunately, I do not know. How can I identify this?
 
The 1-piece block is an update to the earlier 2-piece block. They added another retainer on the back of the block. If you can shine a flashlight up between the flexplate and the block, you should be able to tell. With the flexplate off, it's very easy to tell. If you have a replacement engine, some retained the 2-piece much later than 1985. For example, all Goodwrench engines used the 2-piece.

How to identify a 1 or 2-piece rear main in an SBC.​

The easiest way to tell which rear main seal you have is by the year of the vehicle that the engine came from.
  • 1985 and older are two-piece rear main seal engines.
  • 1986 and newer are one-piece rear main seal engines.
If you don’t know what your engine is out of originally the best place to check is the back of the block. 1986 and newer engines will have a retainer to hold the seal in place. If the retainer isn’t present, see the image below for clarification.
sbc12.jpg
 
Looks like it's a one piece.
Do you have one for sale or know where i can buy one?
 
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