I just had my 350 automatic trans rebuilt and installed a 3200 TCI stall converter to a 350 SB producing about 425 HP. For some reson when I Manual shift from first to second gear it shifts very slow and feels like it is slipping. Any Ideas what is wrong? I would Hate to pull trans again.

Is the vacuum modulator connected and properly adjusted?

-dnult

The vacuum line is hooked up drawing 15-20 lbs.
Any other ideas or suggestions.

Thank you very much,
SOSExpress

The vacuum line is hooked up drawing 15-20 lbs.
Any other ideas or suggestions.

Thank you very much,
SOSExpress

How do I adjust vacuum modulator?

Did you add a shift improver kit when you rebuilt it?? The loose converter won't improve the shifts, it'll just put more torque on the input shaft.

Sounds like it might be a stock rebuild to me?

You can't adjust the vacuum modulator unless you have an "adjustable vacuum modulator".

he, he, he - take out the 1-2 accumulator spring and turn the piston upside down! :eek:

To adjust the modulator, stick a small screwdriver in the vacuum port of the modulator. Counter clockwise will make it shift sooner and lower the line pressure. The shifts will be softer. Clockwise will raise the shift points and line pressure. The shifts will be firmer.

HOWEVER! The vacuum modulator is not the right control for setting shift timing. The govenor is the right place for that. The correct way to set the modulator involves a gram scale - setting the modulator's spring tension for a specific weight / pressure. But hardly anyone does it that way. If you find yourself have to tweak the modulator more than a couple turns in either direction to get your desired shift, you'll probably need a shift kit and possibly recalibrate the govenor.

-dnult

Thanks for the Information I will try that because I know there was a shift kit installed.

I used a governor recalibration kit and shift improver(street/stip) by B&M in my TH-400. graemlins/thumbsup.gif it really beefed up the performance. The 1-2 shift is a little hard sometimes, but I still need to change my driving habits to find the sweet spots. If I'm on the gas(not as far as to hit the kickdown) it'll shift at 30mph and 60mph, with 2.73 gears and 30" tires. This is in my truck of course.

PDQUICK, were you serious about putting the piston in upside down, i don't remember seeing that in the instructions?????

Well, I've done this on a few race only automatic transmissions! It will make the transmission shift 1-2 hard enough to snap your neck!! :eek:

I had an old timer tell me to do this about 15 years ago. Don't know if it's ultimately destructive or not! Most transmission guys tell me that the faster you can get the shift over with, the less you will wear the clutches. Of course, you might rip up the friction discs and the rest of the transmission gets beat to hell!

I am fairly sure what PDQUICK is talking about is a modification a t-400 valve body. Early design t-400 valve bodies had a piston that could be turned over to remove accumilation from the 2-3 shift.

The 2-3 accumilator piston in the T-350 valve body cannot be turned over like this. The 1-2 accumilator piston in the side of the t-350 tranny case certainly cannot be turned over. In fact late design T-400 valve body pistons cannot be turned over.

If you want a faster 1-2 shift I would remove the 1-2 check ball from the valve body. If you want you can remove 3 of the 4 chack balls from the T-350 valve body. The only ball required is the one nearest to the modulator valve.

With the 1-2 check ball removed you will get faster reaction when the shifter is moved from 1 to 2.