727 no reverse, forward in neutral after rebuild

mmbroker68 said
I know its a year later but did you ever figure out what the problem was?

This exact thing is happening to mine. 727 bb, rmvb from turbo action. For a long time wont go into neutral when running unless been driving for a while. If you try when not warm enough it makes grinding/buzzing gear noise (real faint but car is loud). Reverse used to work fince once car warm but now no reverse cold or warm. Forward 1-3 engage but havent driven down road so dont know if working fine while driving. Car will go forward with a little gas if you put the shifter between park and reverse...reverse wheels feel locked. Park sometimes wants to initially jump forward a bit then locks into place. Had pan off and fluid looked good with normal limited amount of very fine metal residue in it....low/rev servo spring etc all in place and adjusted to 2 turns out. Didn't check other band. I also didnt pull the servo out so maybe it has a crack or something? I haven't done any air testing or pressure tests at this point. It started doing this after I had up in air (sometimes front end only) replacing all brake components and front shocks.

My bet is your bellvue spring broke in the rear drum and the forward gear clutches are mechanically applied with no return pressure from the bellvue spring. This is why the car wants to move forward in every gear, including park and neutral. In reverse, the low/reverse servo is applied, coupled with the front clutch. So when the front clutch, rear clutch, and low/reverse servo are all applied at the same time, you have a trans brake application. Hence why in reverse it won’t move. The transmission will need removed and disassembled to fix that issue. I would suggest a billet aluminum forward drum piston (.875” tall if stock drum and hub), metal spacer ring, and late model bellvue spring. That’s the fix. It’s also possible the bellvue spring didn’t break and the piston had so much play between the piston and bellvue spring, that once the piston applied, it could have popped out of the bore. Either way, the taller billet piston, metal spacer ring, and late model bellvue spring are the fix. Looking at $150ish total for those few components.