Had my '72 for a year now and got caught in a unexpected shower yesterday evening (first time I've gotten caught in the rain in it!) I had never used the wipers except when testing them prior to purchase. I had turned the wipers off about a block from home and the wiper door retracted and seated just as it should. Pulled it into the garage and turned off the engine and all seemed well. 3-4 minutes after I turned off the engine, the wiper door decided to raise up approx 1/2" and stay there. I started it back up and the wiper door closed again but every time I turn off the engine the same thing happens.

I'm sure this is not new to you veterans out there so someone can supply me a quick fix....right?

 

Leak in the vacuum storage tank under the driver's fender....looks like a lawnmower gas tank.....

mine had a bunch of stress cracks in it, from constant flexing...un fixable...to just tee the 3 hoses into it, and forget about it...

OR, the wiper door vacuum relay has a leak in the control line going to it....

there are threads on that.....

 

The vacuum check valve in the main feed line from the intake manifold is probably bad.

 

Say where is that vacuum relay located? Also can you expound on what you said about "tee the 3 hoses into it"?

Also, the check valve idea is intriguing. I assume the check valve is in a vacuum line off the intake manifold? Can you tell me where it is located? Maybe when the engine is shut down the check valve leaks a little bit thus allowing the wiper door to raise a little. Then it begins to "hold" at a lower vacuum pressure? If the check valve was completely bad and/or if there was a "leak" in the vacuum system then the door would raise all the way up after engine shutdown?

Thanks for the replies!

 

Your check valve has failed. It is supposed to retain vacuum in the reservoir tank when the engine is shut off. It isn't.... As I stated in my first post, the check valve is "in the main feed line from the intake manifold". It is the metal round can with one fitting on one side and two fittings on the other. Replace it and the filter (the other little round [plastic] 'thing' in that same line).

 

Charley, are you referring to the device pictured in the center of the pic below? I understand this is called the TCS solenoid valve. The pic was taken right after I got the car. I have since hooked it up to the vacuum system but haven't operated the wipers since then.

 

Dagnabit!! Well the pic didn't attach. On the right side (passenger side) of the carburetur on top of the manifold there is a small approx 1.5 inch diameter metal "can" and connected to it is one hose from the base of the carb and one from the distributor. Also I don't see a plastic device or filter in the same line. Maybe the previous owner removed it.

 

The "can" is the TCS solenoid for the vacuum advance.

You need to look at the large vacuum line coming from the intake manifold at the back of the carburetor for 2 things, a plastic inline filter and a metal inline check valve with one line in and two out.

cc

 

CC,

Ok let me try attaching another pic. I think I may have found what you are talking about...

[IMG][/IMG]

 

CC

It is the 1/2" vacuum line at right side of pic coming from the elbow fitting off the manifold at the top and going down to the white plastic fitting and then to the metal check valve?

Roger

 

Not the best picture but you can see the white plastic filter and the silver metal valve in this shot.

 

The aftermarket valves are notoriously wimpy and fail frequently. If you change the filter often (I believe GM recommended anually!), it helps keep them from being contaminated with fuel, made worse by the ethanol content. I change mine every 10K, which works out to every other year or so.

Hans

 

Those are the ones. Thanks for the photos, guys/gals.

 

You got it.

cc

PS did you ever get your wipers working from your other post?

 

Hello everyone. I left town for a few days and am back.

Thanks for all of the helpful info. I ordered a filter and check valve from Bair's. Hopefully this wioll fix it.

CC, I never had any issue with the wipers on my car. They worked fine the only time I have ever used them (right before the wiper door malfunctioned). Maybe you are remembering a post from someone else?

I'll post and let everyone know if this fixed it. I should receive the new parts this week.

 

I thought you posted that they came on briefly then stopped. Sorry must have been another poster. Old Timers strikes again.

cc

 

Well I replaced the check valve and filter in the vacuum line off the intake manifold and it did not fix the problem. Wiper door still raises back up about 3/8 inch 4 to 5 minutes after engine shutdown.

But this time, as I was bending over the right side of the car looking and wondering over the engine bay, I heard a sound like air rushing thru an orifice coming from under the right fender. It was the Wiper Vacuum Relay. I started the engine, let the wiper door seat and shut the engine down. I hear the noise between the 4 and 5 minute mark every time just before the wiper door raises up. Do you think it's a bad wiper vacuum relay or something between the relay and the bypass valve/solenoid valve arrangement under the dash that is the culprit???

 

You should not hear air escaping the vacuum system so suspect the relay since that is the location of the leak.

cc

 

this exact thing is hapening to my 72!! I hear air escaping after I turn the car off on the right side near the wiper door and then the door opens about a half inch ???

 

Here is how your vacuum relay works: Engine vacuum is applied two places. One hose goes to the top of the can that houses the diaphragm. That is the Control circuit.

Below the diaphragm there are three hoses. The middle hose also has vacuum from the engine. The other two hoses go to the front and back of the actuator. Vacuum on one side of the actuator opens the door, and vacuum to the other side closes the door. The relay controls which side gets the vacuum.

Normally closed: Vacuum is applied to the diaphragm which is pulled up so the relay sends vacuum to the front side of the actuator. When you turn on the wipers, or pull the valve under the steering column, vacuum is cut off to the diaphragm so spring pressure pushes the diaphragm down which switches vacuum to the rear of the actuator which opens the door.

If your door is opening after you turn the engine off, you are loosing vacuum to the diaphragm side of the relay. There is enough residual vacuum in the system to open the door.

The headlight doors work exactly the same way. Some cars have two headlight relays in parallel, and some cars have only one relay, but they work the same way.

In theory, this system works just like an electrical circuit with a relay controlling voltage to various other circuits - for instance, a fan control relay turning radiator fans on and off.

Once you understand how this seemingly mysterious system works, it is pretty easy to trouble shoot and fix .