hey guys, i manually shift my th350, and i was wondering if i could disconnect the vacuum line from the vacuum modualtor, becuase i dont need it. will this be alright to do, i figure since i manually shift that it dowsnt need any vacuum, am i right??
thanks alot
Preston
1967 Chevelle- 12.4 @111

Unless it has a manual valve body it won't shift without vacuum until very high RPM's.

------------------
Steve Strasemeier (70SS 396, Fathom Blue/White Stripes)
My 70SS (http://www.chevelles.com/decoder/about.html)

Besides the fact that when you disconect the vacumn line the line pressure goes to full which can wreak havock inside the transmission, I don't think that it will shift into high gear.

If you unplug it...the shifts will be very late, and hard...will never shift out of 1st in the city.
It tells the trans there is no vacuum. No vacuum=WOT=late shifts.
HTH

------------------
'69 Chevelle 2dr Sedan project in progress.

Why would you want to disconnect the vacuum modulator? What are the advantages? http://www.chevelles.com/forum/confused.gif

------------------
MalibuJerry350
TC Member #1279
Original owner '70 Chevelle.
591,000 miles on car.
Hey, if it's got wheels, DRIVE IT!
My Chevelle: http://hometown.aol.com/erie614/myhomepage/index.html

If you disconnect the modulator the increased line pressure pushes the convertor forward, resulting in engine thrust bearing failure.

the reason i asked was because my cam is a 254 260 @ .050 at a 106 lsa, so im not getting much vacuum. what does a manual valvebody do over the vacuum one? does it allow it to shift without vac?? do u think i need one?? thanks
Preston

You can probably find an adjustable modulator valve for that trans. Look inside the vacuum port. If it looks like there is a spot for a screwdriver inside...it's adjustable. It makes the valve shift @ different points, and may overcome your lower vacuum condition.
It's been a few years, I don't remember which way to turn it to correct your problem.

------------------
Don
'69 Chevelle 2dr Sedan project in progress.

I believe in makes it shift later and harder

What does? Disconnecting it, or adjusting it?

------------------
Don
'69 Chevelle 2dr Sedan project in progress.

Disconnecting it makes it shift harder and later. The key thing here is that it will shift later ALL the time, WAY later. It is not a good idea at all. You will be somewhere in the neighborhood of red line for EVERY shift. That would be a major PITA on the street.

Who cares what it does with the trans...?
It wouldn't be there if it wasn't needed right?
It is one of the major influences on shift control in a TH trans.
I would be concerned with the thrashed motor it will cause.
Kinda expensive to have the thrust surfaces welded up on your crankshaft, and thats IF it's steel, if it's cast I wouldn't even weld it.
The additional pressure from having the modulator unhooked pushes the convertor forward in the pump, which in turn pushes the crankshaft into the thrust bearing.
Trans line pressure is usually not more than 160 psi on a TH400 and usually less than 110 except in reverse and Drive 2.
Engine oil pressure is usually less than 60 psi, so it's pretty easy to see how excessive trans line pressure could overcome the oil pressure swedge between the crank and thrust bearing right?
Do it if you want but I suggest keeping the modulator intact.
Leo where you at?
I would suggest finding a large body old style modulator, it has a larger diaphragm and is more effective with large cams. Or even a supercharger cable setup, or a diesel cable setup if for a TH400. Order one at your local Hummer dealership for an older Hummer...