How does the stock TH350 know when to shift?

[team39763]

Does it shift off vacuum readings using that vacuum modulator thing?  I was just wondering because I haven't messed with the modulator or governor/weights.  I usually just shift my truck myself with the ratchet shifter or just put it in 3rd to drive around in the pits.  I was wondering what it would do if I left it in 3rd to race.  It has as TransGo shift kit w/no kickdown and that's about it(was rebuilt with good clutches/steels).  I didn't want to just go out and try it, because I don't like hitting my rev limit.  I broke my tensioner twice by hitting the rev limit a bunch(several people warned me about that).  Will it most likely just shift early or will it hold the gears a little longer than usual?  I really don't care what it does, I just don't want really late shifts when I take off at WOT.  I may go ahead and buy that B&M Gov. recalibration kit.  I'm planning to use the 2step next time at the track, that way I can hit the converter with full force, it'd be nice to not have to shift it myself immediately off the line. 

[SUX2BU99]

I wonder that myself. My TH350 has lousy shift points. WOT is at best 4000 rpm and doesn't downshift anywhere above 2000 rpm.

What's your launch technique? Do you have a full manual valve body? If so, when you are puttering around in the pits, it's in 3rd gear only? Finally, what's a 2-step supposed to do?

[team39763]

Na, mine is a regular auto valvebody.  My launch technique is different everytime.  I've been trying to find a technique that feels right, but nothing seems to feel that fast.  Usually when I try to punch it from a stop, I have to shift before I even get the pedal to the floor.  So I decided to hook up my 2step(basically a second rev limit).  I have it wired to my brakes, so when they are pressed the motor can only be stalled up to what my brakes will hold(3000) even with the pedal floored.  When I release the brakes, I'll already be WOT right off the line.

[VileZambonie]

Up shifts occur when governer pressure rises. Down shifts occur via your detent cable. The vacuum modulator delays an upshift or forces a downshift. You can get an adjustable modulator and you can set your detent cable to help fine tune your sift points.

[SUX2BU99]

Good info Vile. I'll have to scope that out. (speaking of detents, do you have any advice about my column shifter issue?)

[VileZambonie]

Good info Vile. I'll have to scope that out. (speaking of detents, do you have any advice about my column shifter issue?)

What is your column shifter issue?

[SUX2BU99]

http://forum.73-87chevytrucks.com/smforum/index.php?topic=9239.0