Dano86

Good morning all,

Ok, I just got done with the engine rebuild and now onto the transmission. I have a 1978 with 3 speed auto trans. only 55K miles on the car.

Problem: When driving the car it has a hard time shifting. when it does shift it is not a hard shift just doesn't like to go from 1-2 and rarely will go from 2-3 until after high RPMs (3500ish). It acts as if I am going up a hill and doesn't want to shift till after the top and on flat ground again, if that makes since to y'all.

Any idea if this could be something simple like a vaccum leak or maybe a kick-down adjustment? Or the bad news of a rebuild on the trans too?

Has anyone else had this same type of problem?

Thanks for your time
Dano

Red 69

Check and be sure you have adequate fluid in the transmission.

The TV cable should be fully extended when the carburetor is at WOT.

Check and be sure your vacuum line is on the modulator, and the short section of hose that connects the vacuum tube to modulator is not cracked and leaking. Check the intake side of that vacuum line as well.

If the transmission worked before the engine was taken out, it should work the same now. Something is different, did you bolt the torque converter up to the flex plate correctly? It should have lined up with the bolt holes perfectly. Was the torque converter removed after pulling the engine? Go over these items first, chances are it is something simple, but don't run it hard until after you identify and fix the problem, or you risk permanent damage.

Dano86

Thanks for the reply.
Fluid is full, the problem started after i got it out of the shop to have the motor mounts replaced in june right before a vette rally in Spearfish SD (had them do the work bc i did not have time right then to do it myself). if was right after i got it back, bout 50 miles later, that it spun a rod bearing and the transmission was acting up (no problems before they had it). so i didnt get to go to the rally 50 miles from home but enough of that and back to the problem. torque converter was installed and double checked by two different sets of eyes. i will check those ideas and get back to ya probably tomorrow.
Thanks again
Daniel

hugie82

If you have a th350 trans it's a modulator or vacuum going to the modulator. You can also adjust the modulator a little by using a small screwdriver (flathead) and turning the screw in the vac port on the modulator

7T1vette

Your transmission either has a vacuum modulator (modulator on side/back of transmission with hose going to intake manifold vacuum source) or a T.V. [throttle valve] cable. Those items are different methods of obtaining the same thing: modify the shift timing depending on how much throttle is being used....more throttle means later shifts.

If the modulator is not functioning, you will get late shifts. Check for connection on vacuum modulator first; replace the modulator if vacuum line is connected properly. T.V. cable requires proper adjustment: nearly all of the available travel in the cable should be extended when the throttle cable is fully opened (WOT).

Dano86

when adjusting the tv cable should there be something that holds the cable stationary withing the adjustment slot so that it is pushed forward when accelerating and pulled back when not accelerating? right now mine has nothing holding it in one place and is free to move within the long skinny slot at the tip of the cable.

hugie82

If its not (pulling) on the cable during acceleration you would get early shifts at 2-3000 rpm @ WOT

Red 69

The TV cable outer sheath should be held in a stationary position, so the inner cable moves in and out with the throttle linkage. The inner cable wants to retract back into itself, as on a spring, and at WOT is fully extended. If yours does not function this way, it is one of your problems.

Forget about the screw inside the modulator for now, it only changes how hard it shifts. Your problem seems to be with the TV cable, or vacuum leak to the modulator. The modulator is on the passenger side and a disk like thing a little over two inches in diameter.

Your TV cable mounts to the transmission in front of and below the modulator by a black plastic thing held by one screw above the pan. Be sure the plastic mount wasn't broken while removing the engine. It is easy to change out, but will cost you. Under the plastic there is a metal wire clip that hooks the trans valve. Just unhook it and replace, if necessary.

I put a LOKAR unit on mine, along with one of their carb brackets to manage the throttle as well. It is not necessary, but slick and easy to work with. In my case I have a Holley carb and aftermarket intake and stock brackets wasn't getting it..

Dano86

thanks yall for the info. I took the tv linkage off the carb and let it rest on the intake. went threw all the gears like it should, just missing the kick-down for passing without the cable attached. now it will be to adjust the cable and should be good to go.
just wanted to say thanks to everyone again for all your help.
Dano