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Discussion Starter #1 (Edited)
I'm no guru when it comes to transmissions, but this is something that has been floating around in the back recesses of my mind for awhile and I thought I would ask here to see what the answer is.

I understand what a manual valve body is (and the reverse manual valve body too), it is pretty much what it states...you shift the trans through the gears manually. My question is this, when you use a manual valve body, do you still need a vacuum modulator on the trans, or does the manual valve body eliminate this?

And to add to my stupid question, is it possible to eliminate a vacuum modulator, or is it something there is no way around? Again, just learning stuff, no actual reason for my asking other than to find out how it all works together.

Only asking this out of curiousity, no other reason.

Thanks!
Mike
 

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MOST manual V.B do away with the modulator and run constant line pressure. One exception is the 40-3 transgo kit that converts an auto V.B to manual ,it still requires the modulator to be connected to control the line pressure..

For any auto shifting you do need the modulator connected .
 

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Discussion Starter #3
MOST manual V.B do away with the modulator and run constant line pressure.
Thanks! I guess to continue with my curiousity and like I said, I am no guru with transmission (which is why I am asking these questions, to help myself learn)...you wrote that it runs with constant line pressure when using a manual valve body...at the risk of my sounding stupid, how is that constant pressure achieved?

Thanks for putting up with my questions, I tried searching out the info, but pretty much came up with nothing usable.

Thanks again!
Mike
 

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With mods to the pressure regulator valve and pressure boost valve
and by disabling the modulator/throttle pressure circuit . .The manual VB will run usually in the area of 200psi where an auto type VB with modulator is much lower with little load like maybe 80-100 psi depending on VB , and pressure increases then as engine load does by the modulator sensing the vacuum drop/engine load and signals the pressure boost valve.
 

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Can you run a Automatic valve body without a modulator if you are just shifting it manually? or do you need that extra pressure that the modulator kicks in?
 

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Can you run a Automatic valve body without a modulator if you are just shifting it manually? or do you need that extra pressure that the modulator kicks in?
No. Because the trans still makes decisions, even if you are moving the manual lever. In most C4s if the vacuum line isn't hooked up the trans will likely not go into 3rd. If you convert to a real manual VB, the modulator just becomes a plug to keep fluid from running out.
 

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I'm running a PA manual valve body. Can I put a 1/2-20 bolt in the modulator hole to seal it and leave the valve and rod out or do I need to leave those in place?
 

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Look at the installation instructions. Each manufacturer is different and you need to do what they recommend in order to be sure it will function as required.
 

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I'm running a PA manual valve body. Can I put a 1/2-20 bolt in the modulator hole to seal it and leave the valve and rod out or do I need to leave those in place?
You most probably can.You must have a 70 model trans with threaded modulator. What model # PA valvebody?You need to look at the valvebody and see if there is any holes on the seperator plate that correspond with where the modulator is . The PA rev manual V.B i have is blocked off so leaving out modulator is fine.
 

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Good points. I downloaded their instructions but they were vague. I'll look at the passages and see what I can figure out. The VB is fairly new but was used prior to this in my buddy's bracket car.
 

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Update: There are no passages in the PA separator plate leading to the modulator area. I did plug the case hole using a shortened 1/2-20 bolt and the factory gasket. By the way the PA VB uses a stock gasket.

I noticed several of the valves in the PA VB were either *seriously* stuck or otherwise fixed in place by PA. There did not seem to be a bunch of debris in there that would stick these valves. Anyone know if this is normal for the PA manual VBs?

Unfortunately this makes it hard to properly clean the VB...

Another note: there are quite a few modifications to the passages via milled slots. It really looks like they did their homework...
 

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Have a look in the old posts ,one of the guys here has dismantled a PA vb .I'll see if i can find it. He may be able to help more . The valves are sometimes blocked but should still come out.
 

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I have some other pics of a PA body dismantled. The valve beside the pressure reg valve has an allen screw to hold valve inward. Which valve is the one you are referring that is stuck in?
 

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There is no need for the shift valves to move, the backout valve is useless, and the downshift valve should be held solid as well. Beyond that i would have to look at the diagram of the valve body to name any more.
 
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