1970 Corvette Trico vacuum valve

[D S.]

Which way is that Trico vacuum valve (85595) supposed to be positioned? It has two ports one side and one port on the other. When I blow into the single port it's like it's stopped up. When I blow on either of the two ports on the other side it blows through but feels restricted. Does the single port side hose go to the vacuum tank and one of the two port sides on the other side go to the intake vacuum tree? My headlamps and wiper door won't operate without help and I may have the vacuum valve reversed.

Thanks,
Scott Sims
Texas Chapter

[Paul O.]

Re: 1970 Corvette Trico vacuum valve

Scott the single port too engine manifold vacuum and the dual ports one to vacuum tank and the other goes through the firewall. Paul 18046

[Patrick H.]

Re: 1970 Corvette Trico vacuum valve

This should help:

[D S.]

Re: 1970 Corvette Trico vacuum valve

Okay....the hose comes off the manifold vacuum tree to the white filter and to the single port on the Trico and that is an air supply, right? So, f I can't blow air through the single port side how is supplied air going to go through the single port to the two other ports on the opposite side. If I can't blow air through the single port is it defective? What's the test to see if they are defective?
One hose of the two ports on the Trico goes to the vacuum tank. Does that hose supply air to the vacuum tank and what holds the air in the tank?

[Patrick H.]

Re: 1970 Corvette Trico vacuum valve

Okay....the hose comes off the manifold vacuum tree to the white filter and to the single port on the Trico and that is an air supply, right? So, f I can't blow air through the single port side how is supplied air going to go through the single port to the two other ports on the opposite side. If I can't blow air through the single port is it defective? What's the test to see if they are defective?
One hose of the two ports on the Trico goes to the vacuum tank. Does that hose supply air to the vacuum tank and what holds the air in the tank?

No, the intake manifold is a "vaccum" supply, not an air supply.
It sucks, not blows.

From the one port manifold end, try blowing into the valve (reverse of normal flow). If you can't blow, the valve is OK.
You can also try sucking on one port at a time on the other side, but be sure to block the neighboring port. This is not as good of a test, but still useful. There may be a bit of "blow by" on this one.

The hose supplies vacuum, not air, to the vaccuum tank. Hopefully your tank has no holes and "holds" its own vacuum.

[Michael W.]

Re: 1970 Corvette Trico vacuum valve

It operates on vacuum, not pressure. Blowing through either side proves nothing.

[Patrick H.]

Re: 1970 Corvette Trico vacuum valve

It operates on vacuum, not pressure.

Agree. Sort of.

Blowing through either side proves nothing.

Disagree.

It really operates on "relative air pressure," not vacuum.

You want to be able to "keep" vacuum on the non-manifold side of the valve. As such, you want the valve to "close" when the air pressure is higher on the manfold side than the dual outlet side - such as when the car is turned off. Blowing into the manifold's single outlet side sort of "mimics" this - you are providing a pressure higher than the ambient air pressure on the other side of the valve. If you can blow through it in this direction, then toss the valve because no amount of vacuum will hold.

Patrick

[Dick W.]

Re: 1970 Corvette Trico vacuum valve

It operates on vacuum, not pressure. Blowing through either side proves nothing.

Negative pressure, if you wanna get technical about it

[Michael W.]

Re: 1970 Corvette Trico vacuum valve

My my Patrick, you and Dick are in a pedantic mood tonight!

If you want to play that way, a more accurate simulation of operation would be to apply 'negative pressure' at a level equivalent to normal engine vacuum (oops sorry Dickie, negative pressure) on the side of the valve with two outlets. At the same time, the opposite side of the valve with the single outlet (or is it inlet?) should be exposed to atmospheric pressure.

There should be NO flow under the above conditions.

Thank you both for becoming charter members of the NACRS

[Richard T.]

Re: 1970 Corvette Trico vacuum valve

Scott: I have a low mile early build stock 1970 small block Corvette that has not been molested by would be restores. The vacuum hoses on the 70 Corvette are color coded via stripes. The hoses are also bundled with your head light washer hoses. The storage tank under the fender on the drivers side stores vacuum for operation when the engine is off. The operation in this case of your headlight buckets. The system does not hold vacuum for very long after shut down even when the car was new due to bleed off. I recommend the assembly manuel for your 70. The manuel is available at Corvette Central; go to there web site. A hand operated vacuum pump is also handy when trouble shooting the system operation. The book is worth a thousand words.

[Jim T.]

Re: 1970 Corvette Trico vacuum valve

Richard T. I also have a 70 Corvette, mine must of been special. I can remember being able to raise the headlights the next day without starting my 70 that was bought new. I remember this was in early 71 when I actually did this.
Now, today, that will not happen. Everything does work when the engine is running but only when the engine is running. All original except for the filter and metal vacuum valve.