ok i have a 91 700r4 comes with a .095 reverse drum, i ordered a new reverse drum because the old one was too worn so the new one has a large sqaure hole. according to the atsg manuel the large sqaure hole drum will not work in a 91 700r4. only 93 and up ,and can retro fit early 82-87 but suposily the large sqaure hole drum will not work in late 87-92 acording to atsg manuel and i notice the 93 only has a added check ball for this large square hole drum. the place that sold me the drum said it will work in all 87 and up 700r4/4L60es. whos telling the truth here??

 

I just went through this with my build ('89 700R4). The drum with the square hole interchanges on +87 (possibly 82-86 as well) and is a better unit to use.

 

if it has a checkball in the backside of the drum, it is the early '82-'86 model and has a different size piston. the '82-'86 also had a square hole. the '93 and up has the square hole and no checkball in the drum. these will retro all models if used with the piston that goes with them.