Vacuum hose routing?

[ccf460]

I have had my vaccum solenoid/valve on the IP bypassed for so long that I can't
remember where the lines go? The valve has 2 nipples, upper and lower. Which one
is fed by the vacuum pump, and which one feeds the transmission? If someone could
take a quick peek at theirs, I would appreciate it. Also, what seems to be the average
starting position on the side of the IP, mostly forward/back/middle. I put the new
valve on with no change, I want to make sure the top end is right before I go after
the modulator.

 

[cpf240]

I read on here somewhere that it is "Top for Transmission"

 

[ccf460]

I think that I have it backwards then. I was assuming top for the higher (pump), and lower for the transmission.

 

[cpf240]

That is what I read here, and is the way I have mine hooked up (Trans on Top). If you have not done so already, you may need to remove the little rubber block piece that goes between the valve on the IP and the vacuum lines. It tends to rot then leak and is no longer available from any source I've checked.

I'm sure the -20 TM would also show the vacuum line routing, if there are any further questions on it. Oh, and it would be a good idea to get a vacuum gauge to verify the draw from the pump is correct per the TM, and that it is making it all the way to the modulator on the trans. Some have reported that the hard lines rub against stuff and get holes in them.

 

[Keith_J]

I read on here somewhere that it is "Top for Transmission"

Bingo. GM used that keyed connection to assure proper orientation. But since that part is hard to find and always rotten after 25 years, direct connection with this mnemonic in mind makes everything work right. I do believe I coined this phrase

 

[ccf460]

WOW!!!, what a difference a $65.00 part and proper hose routing can do. I bought the truck with a bad valve, it was shifting based on pressure at 35 & 55 mph, and did not downshift until stopped. I bypassed the valve and it shifted way to early. So, I have been manually shifting while searching for the new valve. I bought one , hooked the hoses up backwards and got no relief. Now, it is like driving a real automatic transmission. I think that the valve may need a little tuning, it doesn't seem to downshift from 3rd to 2nd when I apply hard throttle at cruising speeds though.Thanks for the tip!

 

[Warthog]

I think that the valve may need a little tuning, it doesn't seem to downshift from 3rd to 2nd when I apply hard throttle at cruising speeds though.Thanks for the tip!

The valve is covered in the TM

And this thread.

http://www.steelsoldiers.com/showthread.php?50568-CUCV-Throttle-Vacuum-Valve-Adjustment

The downshifting is controlled by the electrical WOT Downshift switch on the throttle pedal and is wired to the switch on the divers side of the tranny.


Two totally separate items.