Why do t-45's like to stick in reverse?

Mustang5L5

That is…until I whipped out my Bissell
Mod Dude
Feb 18, 2001
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Massachusetts
Trying to diagnose a problem with a friend's t-45. His t-45 has become stuck in reverse and he took it into Ford for service.

I have seen it happen quite a few times so i'm curious why does this happen?

Also, does anyone have the tremec rebuild manual .pdf? I plan on picking up a junk t-45 and learning how to rebuild it so i can held out a few friends by rebuilding their t-45's for them. I can already rebuild a T-5 with my eyes closed basically.