Advance adaptor for m-21 to a truck bell housing

[BrianCarroll]

1979 c-10 big 10 sport rpo z77 and f44

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Having a problem getting my fresh M21 4 speed to slide into my truck bellhousing..
truck belhousing appears to have an ID of 5.125 od of bearing retainer is 4.686 id and 5.125 od.
ok I got that but it appears that I am sliding my transmission with the new adaptor (5.125) into a hole of the same dim 5.125. No room to fit ...
last time about two years ago I did this I got it started then used the four bolts to suck it up to the bellhousing with out breaking off an ear> not ready to try that again

 

[Ricko1966]

I'd sand the inside of the adapter and out side of the retainer probably lightly dress the outside of the retainer with a file. Is this all still on the bench or already in the truck? On the bench you could try heating the bellhousing with propane and installing it on the transmission then install the pair as a unit. It's amazing how much things grow with heat.