1970 Wiper door vacuum loss

[Bob H.]

I know this has been discussed often but I cannot find the issue. Wiper door opens temporarily when starting. FYI, I see the buckets barely move like a quarter inch at the same time.

I am pretty familiar how the system works. When turned off, after about 5 minutes you can hear the relay valve that should hold vacuum release thus causing the door to open on restart. The door actuator, relay valve Wiper vacuum switch at wiper, over ride switch and solenoid on tach have tested ok. I can put a check valve before the solenoid and what little vacuum is in the line holds the relay valve fine for a long time.

I have a vacuum pump and connected it at the check valve to listen for a leak I cannot hear a leak anywhere using a stethoscope with the pump outside for silence. I tried listening with a rubber hose stuck up around the light switch and heard nother. That got me to thinking about how the hoses are connected to the light switch. I remember there were incorrect diagrams floating around and wonder if the hoses reversed on the light switch could cause my problem. Of course I can't see them and not even sure if that could be a cause. Everything works as it should except for this leak down.

[Bob H.]

Re: 1970 Wiper door vacuum loss

I am getting closer. There is a "T" on the yellow line just before the relay valve. Who knows where that small hose heading inside goes to?

[Mark E.]

Re: 1970 Wiper door vacuum loss

A quick and easy method for locating leaks is a smoke machine. Less than $100 and a real time saver.

[Bob H.]

Re: 1970 Wiper door vacuum loss

Hi Mark. The leak is in the last place I looked. Once I disabled the tiny hose from the T and the leak is on that what I believe is the heater control s inside. It looks like a check valve somewhere in the system and I have to chase that hose down once ir goes through the center of the firewall. If I can find the check valve, perhaps that is the problem. Its a non air car

[Bill B.]

Re: 1970 Wiper door vacuum loss

Bob,

I had a similar leak. Indeed it was my non-air heater control. Very small leak, but would cause vac loss after shutdown in about 10 to 15 seconds. I just learned to live with it as it wasn't a major leak.

[Mark E.]

Re: 1970 Wiper door vacuum loss

Hi Mark. The leak is in the last place I looked. Once I disabled the tiny hose from the T and the leak is on that what I believe is the heater control s inside. It looks like a check valve somewhere in the system and I have to chase that hose down once ir goes through the center of the firewall. If I can find the check valve, perhaps that is the problem. Its a non air car

What check valve are you looking for? I'm not aware of any other than the one just upstream to the intake manifold and filter. Do you have a schematic of the system?

[Bob H.]

Re: 1970 Wiper door vacuum loss

it was the poor diagram I was looking at and mistook the firewall grommet for a check valve. Never have I taken so long to find a problem! Yes Bill it was my heater control valve leaking. Thought it was the connector but no. I swear there were a hundred hoses I clamped off before finding it. Even then I could not hear the leak and it was working when running.