Dumb C4 Question

[68stang351]

If the modulator valve needs to be adjusted, would that keep it from shifting into drive?

My Fairlane is so quiet, I can't tell if it's shifting into drive or not. I can't feel it either, but then again I can barely feel the 1-2 shift. I don't have a tach to be able to tell. It just feels like it's too wound up at even 55-60 mph with 3.25 gears. It's too quiet for me to hear.

The last time I had the trans out, when I had the front bushing replaced, the guy at the transmission shop said everything internally was in good shape.

Could I tell by driving it with a vacuum gauge hooked up?

 

[68stang351]

I took off w.o.t. (so I can feel it shift) from a stop and let it shift and it is shifting into drive. I guess it just shifts too smooth under normal conditions.

 

[PoppyMod]

I took off w.o.t. (so I can feel it shift) from a stop and let it shift and it is shifting into drive. I guess it just shifts too smooth under normal conditions.

Hi,
A vac leak in the line to the modulator could prevent the up shift. When running a C4, I had an instance wherein, I had no up-shift. Once I got the car home, I found the short rubber hose between the hard line and the mod. was cracked. Replaced, "life is good" .
Good Luck!