Now I'm confused.... Tranny not bad when vacuum disconnected?
 

Hey there,

DIsconnected all vacuum to transmission (black hose) and hoses to modulator on top of valve cover.

Drove her for 60 miles at speeds exceeding 110 mph downhill. Got it hot as can be. Drove up mountains at full throttle in 4th gear at 90 mph. Same conditions that otherwise, 2 hours ago would have caused mad slippage in 4th.

Now it was perfect.

Well not perfect, but you know what I mean, banging shifts, manual shifting as there was no vacuum, but you get the point, the gears held firmly, very firmly.

No slippage WHATSOEVER.

What's up with this? I'm going to redo the vacuum hoses tomorrow and see what's up, I'll also replace that transmission vacuum modulator ontop of the valve cover. Anyway, anybody have any bright ideas that will help?

Chris

Not sure exactly, but you just diagnosed your problem! It's obviously the vacuum system. Now it's shifting "max firm" all the time, including at light throttle - which is not good. It could be the vacuum modulator on the I/P. Test like this:

Put the gauge on the output of the vac modulator on the I/P (the line out to the trans.) Ad idle, there should be zero vacuum. Now blip the throttle. As you move the throttle linkage, the gauge should show vacuum dropping to zero, then back as you release it. If not, the valve is most likely the problem.

You are getting full vacuum to the transmission most of the time, at least that's what it sounds like, and it should only be getting it at idle or very light throttle.

Hey, at least you don't need a tranny! :D

GSXR

Right you are!
You are apparently getting too much vaccuum to the trans modulator. This will give you slushy shifts. Flaring it is called.
Nothing wrong with the actual trans, just wrong message to the modulator.

First find out if there is too much vaccuum to this modulator.
These are adjustable and you can do a search for "transmission modulator" and find some stuff. When you pop off the modulator cap, there is an O-ring, which is easily replaced, do it first then test drive.