Got the new trans in and shifting but the part throttle shifts are too harsh. The TCC engagement feels just as harsh if not worse. I'm thinking these are symptoms of too high line pressure. I am of course going to check to make sure I am getting good vacuum at the modulator. But I was wondering:

A: What pin length are other people using on the 4l80E Vac Mod?
I put mine at 1.345", which the kit says to shorten to soften shifts.

B: How much line pressure should I be shooting for at part throttle and WOT?

C: Transgo does not reccomend towing with a Vac Mod kit. Does anyone tow with theirs?

I am running a Vig 2800 triple disc, HD2 shift kit, and I drilled the "shift firmness" holes in the valve body plate to .120 " (which transgo reccomends for high stall converter)

 

Those feed holes are a problem. A 2800 converter is really not that high of a stall. I think trans go was thinking much higher of a stall when they put that into print. I personally would not drill those holes larger than .093. Vince

 

would that also cause the TCC engagement to be harsh?

 

With a vacuum modulator the pcm is not controlling line pressure.

Try setting TCC Duty Cycle Maximum to 100% and Minimum to 90%. This really helped my harsh TCC lock.

Vince is right. Chances are to really soften up the shifts you will need to replace the plates and go with smaller feed holes. When transgo says high stalls they are probably referring to 3500 -4000 or something. It is amazing how high stall converters soak up firm shifts.

 

Yeah, TCC duty cycle was my next question. I did however already set min to 90 and max was already at 99. The damn TCC is harsher (is that even a word?) than the shifts. Iwas gonna set it back to stock just to compare.

I was a little leary of drilling the VB plate to .120" but figured "what the hell". When Transgo says things like "this is not for sissies" they mean it. I could actually live with the shift quality although it is a little firm. I might try peening those holes shut a little. If not I'll have to get a new VB plate and some how get the plugs from the shift kit.

I hope the modulator pin is the answer to the TCC. I'm gonna try to see what my line pressure is first though.

Thanks Vince and KY,
Alex

 

Called Transgo. They said line pressure should run 80-200 psi. I was runiing 75-200+ psi. the gauge would fluctuate at 200psi / 0 vacuum. I'm pretty sure thats the pressure regulator doing its job.

I shortened the pin to 1.310". Shifts and TCC engagement is MUCH better now. I want to see what WOT line pressure I'm running now. I may keep it like it is and I may shorten it another .010".

 

Max pressure set to 180 psi is plenty for a 4l80e. 180-200 is what I see on our Dyno and that is what we run. Min pressure is about 65-70psi. Vince

 

Exactly where is this pin? How hard is it to get to?

 

It is located behind the modulator. To get at it you need to remove the two bolts holding down the modulator bracket. This photo was taken by blown3qtr. Just linked it for you. Vince

 

Thanks Vince!

In the old days, TH400, the modulators were external to the tranny and adjustable there with an allen wrench.