Lazy 2-3 upshifts

[Rob75383eg]

Howdy Folks!!!
I just came over from another forum because I was told that you fellas have some of the best tranny info around...

A little background/ tech info:
1975 vette 383c.i. 9.4:1 comp. ratio.
TH400 stock gearing, 2,100 stall, trans-go shift kit.
3.70:1 rear gear

I had my tranny rebuilt about 2 yrs ago, and had a Trans go-Shift kit installed at setting 2 out of 4.
From 1st-2nd there is a nice, solid shift, but going from 2nd to 3rd, it seems to be lazy with engaging third gear, sometimes.
For example, if I gun it from a standstill, and accelerate to about 60, she wont shift into third without a little delay. So the motor's spinning at 4k and just waiting for the tranny to get into 3rd.
If I ease into the throttle, and drive her gently, it'll shift to 3rd with no problem. Only when I romp on her, and let off around 60mph or so does it seem sloppy.

I've had two mentors of mine tell me that this is a common side effect of the TH400 rebuild. (neither of them were the tranny guy)
The tranny dude that did the rebuild drove it with me in the car, and could not find a problem with the shifting... he said it may have to do with my style of driving... you know, flooring it off the line, and keeping it down 'till about 55, then trying to level her off at a 60mph cruise speed.

What do you folks think???
Is it my hard driving thats causing it, or could there be something amiss in the trans or the clutch pack, or something??

Thanks in advance!

 

[chris718]

welcome aboard chris from www.ckperformance here .a common problem w/ an automatic /manual 400 is at hi rpms gm designed a system that allows governor oil to be sent to the modulator valve which in turn lowers line pressure on a 2/3 shift.also the accumulator piston in the valvw body leaks around the pin reducing shift firmness .if you want to fix it ,call us and there is a 5 minute modification you can do to the vaccum modulator valve located behind the vaccum modulator on the outside of the transmission that will help.contact us at www.ckperformance.com/718 784 4256