This is my first posting. Just bought a 69 Yenko Clone. Has a 454 with a TH400 tranny and 12 bolt rear end. I was told it has a shift kit. The problem is that the tranny does not shift till you reach about 30 MPH. Then when it shifts it shifts hard. I would like it to shift at a lower RPM. Also shift smoother. Not into drag racing. I have been told by others it may be the torque convertor. I installed a new modulator and it has vacuum at the modulator so this is not the issue it seems. Any ideas?

Welcome to the best Camaro site on the web. You will get tons of help on just about anything. Now, Try adjusting the vacuum mod. (if it's adjustable) with a small screwdriver. Remove the vacuum line and look in. You should be able to see where the adjustment is. This morning, I can't remember which way is which. Kevin

Yah, tried that with no effect. Counterclockwise is lower RPM shift. According to the instructions .

Is there vacuum at the hose where it attaches to the modulator?

Does the modulator diaphram hold a vacuum?
Is vacuum source & tubing in good shape?
How much vacuum is created at wanted shift point?
Have you tried using a MityVac to control modulator?