70 Skylark, was 350 car at one time but someone put a 455 in it. The TH350 is still the trans and since I got it she has always shifted too soon during part throttle and WOT. Detent cable is adjusted and vacuum is manifold for modulator with no leaks. So I'm gonna roll up my sleeves and try to learn a little something about the dark art of transmission tuning. Any advice on a good governor kit and modulator brand? Also any advise for my first time attempting this?
https://www.summitracing.com/parts/...srese1-_-b-m&gclid=CMK6yI_mzNMCFZCPswod_IsE7w Read the instructions. Change one weight at a time. Evaluate with a road test. The weights get you close, the springs fine tune. Good luck.
The cable on a TH350 is just for kickdown; not for general control of shifting. You can have some effect by adjusting an after market vacuum modulator, but I see this as a means of setting harshness, then relying on the governor to set the speeds. It takes many turns here to make a discernable difference; keep records of each setting, which needs to be driven some to properly check. My method is to adjust gov weights for WOT shifts, when rpm is high. And use the springs more for part throttle. Back and forth some a few times will be needed to get it right. I find a spare governor to do the calibration; save the original. Once a weight kit has been optimize, I grind down the gov weights to work, and put the calibrated ones back for next time. Good luck with the small TH350. Bruce Roe
The kit Larry posted is a good kit, many have used the same one. IIRC, I purchased the TCI "red stripe"th350 adj. Modulator with no complaints. you will loose some fluid, not a lot but enough to check level if your in there 2-3-4 times. When you go to put the governor cover back on, tap around the outside edges not the face.
Bruce from what I have read about the THM350, the detent system does in fact have some effect on shifting. The detent pressure regulator valve will extend the WOT shift points, so a missing or maladjusted cable can cause some short shifting. The THM 400 will short shift as well without a functioning detent system. The Ron Sessions THM 350 book mentions checking the detent system if shifts are early, late or nonexistent, especially at WOT.
Excellent advice guys I really appreciate the tips and recommendations. As I read all this and got the plan of action thought out I was left with a question since I was told to make small changes and note results to keep it simple. Should I plug vacuum to the modulator to remove that variable like the advance on a dizzy so I would only experience governor changes? Or is there no harm in leaving it hooked up?
No, at WOT, there is no engine vacuum, so no vacuum to anything, distributor, or modulator. Leave everything hooked up.
I wouldn't do that, not sure about WOT but my rubber line came off one time and the car would not shift into second gear during normal driving acceleration. It very well may have but I let off because I knew something was not right. I would just install the modulator first and get it out of the way so you can then concentrate on the shift points.
I am no TH350 expert, but it does have a vacuum modulator. I read the detent is for kickdown, makes sense, but perhaps the cable could have some other effect. Bruce Roe
From my limited tinkering with governor weights and springs, the governor controls WOT shifts. The vacuum modulator controls part throttle shifts, when vacuum is high and RPM is low. The detent cable controls downshifts. I use the B&M kit for the governor.
