[mark67ss]

I have read a couple of articles and although I am not an expert, I think I have it down on how to set up the th350 shift points. Any tranny gurus please correct me if I am wrong. Basically the shift points are set by the governor and the modulator? using springs and weights. The weights effect the 1-2 gear shift points while the springs effect the 2-3 shift point. Shift points are controlled by the vacuum brought to the modulator from the motor at part throttle and regular driving conditions. So the tranny will switch from 1-2 via the weights and the 2-3 via the springs thru a vacuum translated pressure signal the modulator sends to the governor.

This all changes when you mash on the pedal at WOT. At that point the detent cable is pulled fully out and the modulator signal gets disregarded by the governor. Depending upon how the governor is set the tranny will shift up to the highest speed set by the weights and springs inside it. SO am I right to assume that this is how it works generally? I am guessing alot of fooling around with weight and spring combos is going to be had to find the optimal combo? My tranny shifts way too soon at part throttle and does not kick down fast enough at full throttle if not at all. I want to make my tranny alot more responsive so that it will be better suited to the power band in my motor hopefully making it more fun to drive. Any info anyone can shed on this would be great. Especially on how to set the cable properly.

Thanks In advance.

Mark
TOOFUN

[dnult]

You are mostly correct. The weights vs. springs on the govenor doesn't control 1-2 and 2-3 quite as you have described though. Both control shift points, but in a non-linear fashion. I can't give you the details since I don't recall off hand, but here is what I think happens. The weights give you a more linear shift point change where the springs are non-linear. The result is the weights come into play sooner - thus your conclusion about affecting the 1-2 shift. The springs come into play at higher speeds. I could be wrong, but this is basically how it works.

The modulator controls shift points and line pressure in relation to engine load. High load means low vacuum resulting in later shifts at higher line pressure.

One thing you didn't mention is the shift valve springs. They have a greater affect on the 1-2 vs. 2-3 shift points. Although weights and springs on the govenor do alter the linearity of the shift point curve, the shift valve springs will have a greater affect. Stock THM 350 transmissions have a reputation of running too long in the gears. Many shift kits change the shift valve springs to correct the problem. Transgo kits are one of several examples that I'd recommend.

But after all this, the govenor is a good first place to start. If this tranny is a transplant from another vehicle, it's govenor is likely calebrated to a different rear-end gear. The modulator is another adjustment point. There is a tiny screw just inside the vacuum port. Turning it in will make it shift sooner at a lower pressure. Turning it out will have the opposite effect. But the modulator shouldn't be over adjusted. It needs to operate close to it's calibration point or else line pressures can get out of whack causing premature clutch failure. The calibration point on the modulator is set using a gram scale to set the 0 vacuum spring weight.

[mark67ss]

Thanks for the info. My major concern is that the tranny shifts almost immediately into second gear from a stand still starting position. The motor doesnt even come close to getting into its first gear power range before it shifts into second and starts off in too low of an rpm to get any UMF out of it. If I manually shift it it is great, but dont want to go that route all the time. Secondly, my tranny does not downshift when I mash the pedal to the floor. Sometimes it will but other times it just wont. There is that soft spot in second gear or sometimes in third where you want the power immediately and mash the pedal, it is disheartening when you dont get that down shift burst and have to waste valuable seconds manually downshifting to get the results you want.....

mark
TOOFUN