Howdy all,
I know this has probably been beat to death already, but I can't find the info that I need.
I had rebuilt a 700R4 from an 88 Z with all performance parts. A full kit(frictions, steels, band, seals, ect...). Corvette servo and boost valve. I had done all the VB tricks to have performance shifts. I have put in a delco pressure switch kit for the TC lockup.
I have no 4th gear. I have good hard 1-2 and 2-3 shifts, all at the same rpms each time(I'm only doing light throttle,on jack stands, til I figure this out).
I have checked my work on the VB 5 times, checked the TV travel distance in the transmission and at the carburetor each time I had the pan off. I have also checked to make sure there are no sticky valves in the VB. I have pulled the servo to check my work there.
Everything I have checked appears to be within specs, yet no OD.
Any techs out there that could point me in a direction that I haven't thought of?

 

Check the 4th apply piston in the servo assembly. It's the piston that's next to the servo cover. Make sure it isn't in backwards.

 

Yup, the longer shoulder is toward the cover.