1964 Rear vent hissing noise in center console

[stevetheweave1]

Trying to get Christine, (Stephan King movie), back on the road where se belongs but she keeps fighting me. I know vacuum is cars lifeblood but I continually get a hiss from what I think is an air regulator for rear vent diaphragms? (pictured) I have struck out on my own and screwed thing up before so I do not want to turn adjusting screw and break it. Hisses with vent closed and open. Thinking about folding some dense foam around it so the noise goes away or at least muffles it.

 

[64ZCODE]

It's vacuum actuated and you have a vacuum leak.

 

[stevetheweave1]

Trying to get Christine, (Stephan King movie), back on the road where se belongs but she keeps fighting me. I know vacuum is cars lifeblood but I continually get a hiss from what I think is an air regulator for rear vent diaphragms? (pictured) I have struck out on my own and screwed thing up before so I do not want to turn adjusting screw and break it. Hisses with vent closed and open. Thinking about folding some dense foam around it so the noise goes away or at least muffles it.

Thanks 64zcode so are you saying the way it regulates is by leaking or I have a problem and it is leaking? If it is not right do you think I can disassemble flat plate that is staked and maybe clean it?

 

[64ZCODE]

I think it's the latter, in other words there isn't a controlled leak in the system. The vacuum line runs from the passenger side of the engine, thru the firewall, to the rear vent switch on the center console, then back to the rear vent actuator under the rear deck. Seems likely there is a leak in the vacuum hose where it connects to the rear vent switch, or possibly the switch itself is leaking.

 

[ak7an]

If my memory is correct that is a vacuum regulator of sorts, by adjusting the knob it would control the speed at which the rear vent opens and closes. Just bypass it and eliminate the vacuum leak or you could take it apart and see if there is on oring or seal that can be replaced.
Hope this helps..
Ed

 

[stevetheweave1]

My picture doesn’t show it but there was a small round foam cover on backside that disintegrated when I touched it. Now knowing that it is not normal to hiss I now know that the form was not a muffler but a inlet filter. I will attempt to take it apart and see if there is pieces of the foam filter inside causing a problem.

 

[Angry Bird]

In all likelihood, it's a vacuum hose that has dried out and split. Usually it's where the hose connects between the open/close switch or where it connects at the rear control. Good luck!

 

[stevetheweave1]

Tore apart what appears to be a check valve upstream of rear vent control switch. A little background info car has all new vacuum hoses and vent switch and rear vent actuators have zero leakage. 1st pic larger fitting is the vacuum side it works in that if there is vacuum it goes past round black disc and continues onto smaller port (vacuum just passes straight through). But if larger port has pressure applied then black rubber disc closes and there is no pass through to smaller port. The other side of the chamber has the smaller fitting in common with the white screw. The white screw had foam ring around it that disintegrated. The white screw is tapered and was bottomed out in assembly. Turning the screw while air is flowing through smaller port seems to make no difference. It seems as though air was meant to leak at white screw which is making the hissing noise that sounds like radio static. Could it be a designed leak so as not to rupture rear vent diaphragms or to allow the vacuum to bleed off so that vacuum is not trapped and vents can cycle back closed? If there is no answers out there I am just going to put it in a folded piece of open celled foam to muffle the noise or just bypass it.

 

[ak7an]

Out of the service manual.....

 

[stevetheweave1]

Ak7an I must I have overlooked that part in the manual a dozen times. The bleed down time makes sense if it was downstream of the switch but mine is upstream. All the diagrams I have seen show the adjustable valve down stream of the on/off valve unlike mine. The quarter inch vacuum hose from engine hooks to the adjustable valve then the eighth inch hose hooks to adjustable valve and on/off switch that has two eighth inch fittings. I see no way of hooking it all up that makes sense so I am just going to bypass it. All it appears to do is bleed air off after shut down. Thanks everybody for the help.