how do racers get their race cars to shift with big cams influencing the vacuum?

external vacuum pumps, canisters, modulators?

 

Manual valve body.

 

2X Bobby. As I recall a lot of guys would also make it a reverse pattern manual valve body.

 

Okay. Mine is full manual. Forward pattern though. And it has trouble getting into 3rd and shifts hard as @#$% going into 2nd going any faster than 10mph. So I just start in second now. What should I change here.

 

Who built your transmission? What brand/type of shift kit?
Shift issues are difficult to diagnose once someone has already been in there.

 

i rebuilt the transmission with a transtar rebuild kit using alto red eagle clutches. an f code band apply lever. stock servo-not an r code. 2.5" alto red eagle band, koelene steels. new o rings and seals throughout the entire unit. the air tests proved to be good. the valve body has a fairbanks shift kit with the separator plate drilled out in the specified location to .125" which was the biggest the kit recommended for higher line pressures. took out the checkball that enables auto shifting and downshifting protection in high rpm. in the forward drum i reduced the thickness of the top pressure plate to accept one more steel and clutch. clearance came out to .019 and the reverse drum got an extra snap ring groove a little bit higher to accept more steel and clutch as well, that clearance figure came out to .023, after all was said and done no binding and the tranny shifts fine, just not into 3rd every time and hard into second. my winters gate shifter hits all the gears solid, i can feel the detents in every gear.

i'm beginning to wonder if i drilled that hole too big on the separator plate or if i should just get a different shift kit all together. what do you guys think? the tranny received the shift kit job before i totally rebuilt it and it did this same thing...so conventional thinking would lead me to think that i @#$%ed something up during the shift kit stage...on the other hand i never hooked up the vacuum modulator before the rebuild either, so it's hard to say if its the valve body or the modulator. but they are a part of the same system so its like saying the same thing i guess. if it is the modulator, then it could be that i am not pulling enough vacuum, it it's the valve body it could be the shift kit i used. the shift kit issue can be remedied, but pulling more vacuum from a larger cam??? do i even need the modulator if im in full manual mode?

 

You are above my personal expertise in automatics. Hope someone else will chime in. But I can tell you too high line pressure is why it's slamming in to 2nd. And in full manual mode the modulator is a non-issue.

 

ill run with that then, and try to lower the line pressure. but i got a new modulator to eliminate that variable. thanks for the reply jeff

 

So you have a manual valve body? Meaning it will not upshift or downshift on it's own?
If that is the case then that is why your 1-2 shift is so hard. I have no answer for the no 2-3 shift unless something was installed incorrectly in the VB. It really just sounds like your line pressures are off the chart.
I have a TransGo 67-3 kit in my truck. It reprograms the valve body to improve shift overlap and also gives manual control unless the selector is in D. Meaning, if I'm in 3rd gear and I move the selector to 2nd or 1st, it will downshift to 1 or 2 no matter what speed I'm going. Left in D, it upshifts and downshifts normally but with firmer, more positive shifts. I'm running a D servo cover with an E lever and a stock band and my 1-2 shift is awesome.
The thing I like about the TransGo kit is that the shifts aren't real hard unless you're WOT.
Maybe grab a VB from another C6 and install a more streetable kit.

 

Yeah I agree. I might just do that. I've heard lots of good things about Transgo. The Fairbanks kit reprogrammed the VB with springs and what not too and it also will downshift no matter what rpm or speed you're going. I am definitely getting the feeling that its the valve body now. Thanks for the reply.

 

so heres an update. i overreact.

the cam doesnt do crap to my shift points, vacuum is fine for shifting. i installed the tci adjustable vacuum modulator and the thing shifts into 3rd now. the second gears more tolerable on the firmness. i guess my last modulator was toast.

i still get nervous driving this thing, and that's an awesome feeling you don't get from a lot of today's affordable cars or trucks. for the amount of money you would spend buying a new ford raptor with the 6.2L in it, you could have an amazing older vehicle that performs just as well as the new car. plus you can tune it yourself, fix it yourself, or take it anywhere to get fixed for that matter, buy parts for it at just about any auto parts store, all while getting to where your going in style and having a smile when you pull up. how many modern rides can do that nowadays? oh did i mention sidestepping outrageous registration fees and if you have the right year, being exempt from smog requirements.

 

Glad you got it figured out.