1964 Mustang tranny C-4 Upshift problem

k0rupt3d · 10-11-2009

OK so my cars been siting in my garage for about 1 1/2 years due to ripping the motor apart and rebuilding with some performance upgrades.

So i got it to the point to take it out and test drive so I put all new fluids in the motor and tranny and preceded to take for a test drive and the tranny wont up shift automatically. But manually it will shift through 1st and 2nd with no problem.

Any ideas on what it could be guys?

Again its a 1964 mustang with the stock C4

429ragtop · 10-12-2009

Quote:

Originally Posted by k0rupt3d

OK so my cars been siting in my garage for about 1 1/2 years due to ripping the motor apart and rebuilding with some performance upgrades.

So i got it to the point to take it out and test drive so I put all new fluids in the motor and tranny and preceded to take for a test drive and the tranny wont up shift automatically. But manually it will shift through 1st and 2nd with no problem.

Any ideas on what it could be guys?

Again its a 1964 mustang with the stock C4

Did you re attach the kickdown rod?

Ranger1 · 10-12-2009

Did you reattach the vacuum modulator line?

What did you do to the motor, high rise intake and performance cam? If so maybe the vacuum is now changed and the modulator need adjustment.

The Greek · 10-15-2009

Check for signs of fluid in the vacuum hose at the modulator valve. If there's fluid, the M/V is junk. Also check to see if the steel vacuum line from the valve isn't pinched or crimped and that it's attached to full manifold vacuum on the upper end.

Check the down shift lever to see if it's installed upside down. There is supposed to be a return spring attached to it. This is to keep the down shift lever from moving forward until the time that it's engaged. When it's upside down, and the spring is pulling it back, the downshift is always engaged. This could be the problem.

PaulS · 10-15-2009

If the C4 has been sitting for a long time then it might be anything from what has been suggested to a stuck governor valve or the valve body being gummed up and the spools are stuck in their bores.
If the kick-down is connected correctly and the modulator and valve are ok then you can drive it warm for a while to see if the spools free up. It might take a thorough cleaning to get everything free and moving properly.