I know, I know.
Everyone freaks out if you don't run a pcv valve.

I have been fighting the way may car shifts for a few months.
I finally called a tranny shop. He said I will not get
my tranny to shift if I don't get my vacuum up.

Short version I plugged off all vacuum ports and tested my vacuum.
13hg at idle, 9 hg in gear. I hooked up just the tranny, 13hg at idle,
9hg in gear.

Guess what, the tranny shifts.

After hooking everything up one thing at a time I found that the pcv
valve is causing the loss in vacuum. With it hooked up I am 12hg
at idle and 7hg in gear.

That is to low to let my tranny shift. It shifts at 5500 rpms with the
pcv valve, and 3200rpms without it.

I need those 2hg of vacuum pressure.

Any ideas how to run a pcv valve and not loose 2hg?

 

You can just eliminate the pcv valve and run breathers with tubes to your header collector to scavenge crankcase pressure off the engine. It will work better than the pcv valve, and also gain a slight amount of HP too.
Most serious racers go this route. You'll need the breathers with the hose connection out the side and a tube welded into the collector to hook the hose from the breather. Best to do both valve covers too.

 

You're thinking bass-ackwards here. The vacuum modulator raises the shift points when it's getting LESS manifold vacuum, not more. When your gas pedal foot is down, opening the carb all the way, manifold vacuum drops to near zero. By lack of vacuum, the modulator knows the engine is under a load, and holds the shifts higher. Do you have an adjustable modulator on your trans...yet? And your tranny shop guy said you need more vacuum to raise the shift points huh? Hmmmmm. Or, am I misunderstanding, and you're referring to the shift point being that high driving normally?
Automatic Transmission Modulator Valve - Governor - Throttle Cable

 

Tranny shop says you need at least 13" at idle for a TH350 to shift with any vacuum modulator.

Yes, I have an adjustable one. I have tried taking the adjustment screw out and it still shifts that high. According to B&M a vacuum modulator will only let you adjust it 2-4 mph hour. I am about 50 mph off.

Yes, normally driving with kickdown unhooked and a pvc valve it shifts a 5500 rpms. Holding the pedal to the floor it shifts at 6500 rpms. Tac is fine I can tell my rpms are that high when the tires are spinning and the front wheels come off the ground.

Adjusting modulator makes it shift hard or slip. Adjusted in I get a scratch, adjusted out the tranny slips. either way it shifts at 5500 rpms.

Without a pvc valve it shifts at 3200 rpms and drives rather nice considering.

Trannys shifts with more vacuum. With no vacuum the tranny thinks you are pressing down on the pedal. When you let off the pedal your vacuum goes up. Only mine doesn't go up high enough to up shift.

My kickdown is hooked up, I unhooked it for a month to see if it was causing any issues. It isnt.

The issue is 100% vacuum. I have tried three different vacuum modulators.

 

Problem solved ...Manual/Automatic Valve Bodies

 

LOL, that is what the tranny shop owner said.
but its in a c10, column shift.
I am thinking about installing a floor shifter.

 

Have you checked the PCV valve out? If it is stuck open it will act as a vacuum leak.

 

Are you saying that untill you get to 3200RPMS the trans does not SHIFT?? IF you put it in DRIVE and drive away and only let the engine rev to say about 2500 RPMS it WILL NOT shift out of 1st GEAR???

 

Actually, I was saying that it wont shift till 5000 rpms.
If you put it in drive and let it rev at about 2500 you will never shift.

I only have 7" of vacuum. So for me 2500 rpms is like
having the pedal to the floor. The joy of a large cam.

 

Given all that, your option is to forget the PCV valve and rely solely on dual valve cover breathers, or install an exhaust crankcase evacuation setup, or an electric evac pump setup.
exhaust crankcase evacuation....it works - Corvette Forum