I just picked up a 1991 Z/28 with a 350 and 700R4. I have rebuild at least a 100 700's so I have some know how and diag under my belt. I just can't figure this one out.

Upshifts and downshifts perfect when doing it manual. Holds every gear and shifts firm.

When shifting automatic the tranny does some weird stuff. First it dosen't appear to slip at all in any gear. From secound to third gear the car accelerates to about 3,000-3,500 and then falls flat like its being draged down. You can feel it slow and hold that RPM, no slipping like its max RPM was reached. You need to let of the gas a bit to get it to shift, it goes in third not hard but not slidding either. It also does this same thing on a 3-4 shft. It just hits the 3,000 area and drags. I can't tell if the 1-2 shift is like this because the car will not keep the tires planted. To little throttle and it shifts before the problem and any more than 1/2 throttle and its sideways. Even rolling off the line and punching it puts the car into a kickout. Now say i am driving along in 4th and step on the gas the tranny down shifts to third and accelerates but very slowly the tach is moving really slow and the MPH's are doing the same, feels like driving a standard and not down shifting to accelerate but you could feel the car downshift and see and feel the rpm's pick up. At this same time if i move the shifter to 3rd the car pulls hard and the rpm's go up but not like I downshifted. The engine rapidly accelerates from the same rpm as before i shifted, no quick rise in rpm like a 4-3 down shift just a rise like I steped on the gas. Moving the shifter from 4-3 dosen't make the car downshift its already downshifted from me steping on the gas, it feels like I hit a small NOS hit and the car pulls. If I shift manually I can pull 5,200 rpm's easy but if the car does it automatic it will only pull about 3,500 and slow. It feels like the TCC was being applied early and not releasing untill I stop. Causing the engine to pull hard and slow in each gear and when i down shft manually the clutch disengages and the car pulls. I unhooked the plug from the tranny so the clutch wouldn't work and still the same.
Help

 

It sounds like you are comparing a downshift to the TCC unlocking. When you are in 4th, and you give it more gas, perhaps its just the TCC unlocking, then when you manually downshift, that small "shot of NOS" might actually be the 4-3 downshift. Just a thought.

 

I can't feel the TCC release when I tap the brakes or see the RPM rise. When it shifts automatic from 4-3 its more than a few hundred RPM difference like the clutch disengaging. Its around 800 RPM's. When the transmission is downshifted to third and I just move the shifter to third we should have nothing happen because its in third already. If it was in 4th still and I moved the shifter to third the engine RPM's would increase because I am now shifting it in by hand and it never did it before. In this situation when I shift by hand to third and the tranny is already in third, I don't get a manual downshift indicating stilll in 4th. I don't get anything, indicating the tranny did its job and shifted to 3rd before me. What I get is an increase in acceleration, thats noticable like a 50 shot of NOS, and the car accelerates past 3,500 and keeps going. Automatic the car downshifts and won't go past about 3,500 RPM"s. At this 3,500 rpm's if I move the shifter to 3rd and the car was still in fourth it would force a 4-3 downshift and the RPM's should jump say 800-1000 rpm's real quick because of the gear change. However when I shift the shifter the RPM's stay the same, no noticable change but the car picks up power and the rpm's move along steady untill I shift. The only thing that I could think of that would cause this would be an engaged TCC. That would limit RPM's by making the engine work harder and keep it slower and would cause no major noticable change in RPM's when disengaged (when shifting from 4-3 manual if that caused it to release) but when disengaged would allow the engine to pull higher rpm's, quicker, giving it that 50 NOS shot, that I feel. I unhooked the harness and no change with the converter unhooked?

 

Please Help, 30 people checked this out and only one response. Come on I have been checking this board out for years and if I know one thing its that thirdgen.org users like to give opinions or let every one know that they are the tranny expert. I think I have the car sold tomarrow but not if the tranny does this, I need it fixed today.

 

I'd change the TCC solenoid. Some of your observations point
that way, and it's cheap.

 

Sounds more like a fuel flow problem.

 

I agree with Leo, if the transmission were doing this, and it was between two gears at once, it would be fried. Sounds like fuel problems, but some of it could be torque coverter lockup.