So I'm tearing this 700r4 down for a rebuild and found the 1-2 Accumulator piston stuck in the bore. It's stuck in there pretty good. Anybody ever encounter this? Maybe this is why they junked the poor firebird I got it off of. If this is the case you have no second gear right?

 

No. If the accumulator is stuck, then it doesn't accumulate.

Its job is to absorb the first incremental bit of fluid being sent toward the band servo for the 1-2 shift, to cushion the shock. If it's stuck, i.e. not accumulating, 2nd gear probably slammed pretty hard.

 

Incidentally, you can eliminate the pin that it rides on, by getting "pinless" ones from Sonnax https://www.sonnax.com/parts/2520-pi...tor-piston-kit and maybe others. The same part fits both 1-2 & 3-4. Drill acoupla holes in the factory one(s) if you want, yank out with a dent puller or something, clean up the bore(s) if necessary (probably not but heh...), and put the better one(s) in instead.

The more usual way they fail is by wearing the pin bore to the point that the fluid all leaks out and no pressure every builds up. Hence the point of the "pinless" design.

 

Cool. Thanks for the info. Much appreciated. I'm gonna try swapping housings. Piston looks good, just gets stuck in the housing.

 

The pin must be in there straight and tight. The piston must not wobble on the pin or replace it. Most of the time the pin is worn and the pin hole in the piston is worn out. Bore must mot have any scratches. If there is any scratches and they cannot easily be smoothed out, you will need another housing. If you are using a TransGo Shift kit, you will not be able to use the Sonnax pinless setup.