<VV> Modulator valve vacuum specs

Stephen Upham contactsmu at sbcglobal.net
Mon May 12 20:26:31 EDT 2008


From: Chris & Bill Strickland

If "removing the valve body" is "getting that deep into the
transmission", boy!  you'd just better overhaul that sucker, then when
you are holding the sprague clutch in one hand and the planetarys in the
other, then you will know what "deep" actually is ...

So we next get to 12 - 16 " vacuum -- let's see, where does this vacuum
come from?  Manifold vacuum.  and that gets to how is your car running?
What is the manifold vacuum, by measurement, while driving?  And have
you tried test driving your car with both the modulator hose
disconnected, and then with full vacuum applied (via pump) -- should be
able to learn something that way.  ...
Now, if you just want an excuse to overhaul a PowerSlyde, may I suggest
you get a core from somewhere and overhaul that one -- ...you can  
swap it into your car
and see what you got for your efforts, and if'n ya ain't happy you still
have your old (working) unit.

Or, maybe you have a combination of things all being balky at the same
time -- what's the debris field in your pan look like? -- Keith's looks
normal.

Bill Strickland	O.K., it sounds like an exaggeration to say that I'm  
"getting that deep into the transmission", especially after  
completely rebuilding and assembling the 110 with help from my local  
club members, but it's not really.  I'm an elementary teacher by  
trade.  My dad was the general and Corvair mechanic, but refused to  
allow us to watch or participate in repairs as he didn't want us to  
become mechanics.  I do think that he would be proud to know the  
amount of personal time, effort, and expense that I have gone through  
in the last six years to bring his flagship Monza back from the dead  
after my brother purposely destroyed the engine.
	The 12-16 HG of vacuum that I speak of is coming from a Mityvac  
attached to the unused modulator.  I'm just trying to determine if  
this is within specs as to avoid doing a lot of work to replace the  
current modulator with an already defective new one.  I have not  
tried to drive it with the modulator hose disconnected, though if it  
doesn't hurt: why not?  As far as driving the car with full vacuum  
applied, I can only think of one way to do that and that would be  
with the Mityvac attached to the crossover line near the firewall.   
Sounds challenging, but doable.
	The idea of getting a used PG to "play" with sounds intriguing.  I  
would like to have a reasonable shot at getting the overhaul right  
though considering that I would have to drop the engine TWICE if it  
didn't work.  One thing that I definitely have to do is to adjust the  
"L" arm throttle linkage on the side of the PG.  It is sitting with  
the forward connection link sitting above the gasket line.  My main  
problem is that I've tried to do this twice and each time somehow  
forced the tine to bend on the transmission throttle valve inner  
lever.  It pressed past the detent valve nut and ended up stuck in  
wide open throttle.  My adjustments seem to take a jewler's touch.   
This required dropping the pan and bending the tine back in place!
Oh, and the debris field looked like gasket type material.  Thin and  
hard, about 1/4" in diameter and curved.  Definitely not gasket  
material from the pan.

Stephen Upham


From: Chris & Bill Strickland <lechevrier at earthlink.net>
Subject: Re: <VV> Modulator valve vacuum specs

If "removing the valve body" is "getting that deep into the
transmission", boy!  you'd just better overhaul that sucker, then when
you are holding the sprague clutch in one hand and the planetarys in the
other, then you will know what "deep" actually is (assuming a Vair PG
has these parts, commonly found in many automatic transmissions -- never
had a broken Vair PG in need of repair).

Anyway, first you want to be sure of your diagnosis before you start
repairing stuff (didn't somebody just say the same thing about
electrical repairs), then you go about fixing it.  Fixing it is
replacing what's broken -- overhauling it is replacing a large number of
worn but still functional parts with what you can find, and as soon as
you are done, hopefully you now have a bunch of about to be worn but
still functional parts.

Note that one guy's "kick like a mule" may be another's "clean crisp
shift".  Generally occurring on the upshift though, and not the  
downshift.

So we next get to 12 - 16 " vacuum -- let's see, where does this vacuum
come from?  Manifold vacuum.  and that gets to how is your car running?
What is the manifold vacuum, by measurement, while driving?  And have
you tried test driving your car with both the modulator hose
disconnected, and then with full vacuum applied (via pump) -- should be
able to learn something that way.  The modulator is sort of like a
marriage counselor -- getting two disparate parties (engine and
transmission) to talk to each other so they work like a unit -- each
vehicle has it's own unique set of operating parameters, and those "book
values" for how the modulator should work is more like the 'Pirates III'
"guidelines", a place to start, if indeed the modulator and vacuum
levels are malfunctioning.

Now, if you just want an excuse to overhaul a PowerSlyde, may I suggest
you get a core from somewhere and overhaul that one -- sounds like yours
still works -- then when you get it done, you can swap it into your car
and see what you got for your efforts, and if'n ya ain't happy you still
have your old (working) unit.

Or, maybe you have a combination of things all being balky at the same
time -- what's the debris field in your pan look like? -- Keith's looks
normal.

Bill Strickland


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