Here is the issue. When I start the car the wiper door raises for a couple minutes then goes down. Headlights work great. I have changed the relay/switch valve behind the tach, valve under the wiper arms, the wiper relay on the fender well, all new hoses, the check valve for the vacuum supply that is above the intake manifold. I have bypassed the over ride switch still the same. When I turn the wiper switch on the door raises after about 90 sec and the wipers operate, shut them off and it takes the door about 90 sec to go down. When I pull the white sensing hose off the wiper relay on the fender the door shoots up. I cannot find a leak anywhere, my vacuum guage shows a steady 16.

 

My darn car does about the same thing. When I fire up the engine, the wiper door goes up but comes right back down. On my car, this is the least of my problems.

Wyatt

 

Any vacuum troubleshooting gods want to step up

 

The vacuum control side of the wiper system probably has a leak or malfunctioning valve. This includes the electrically operated vacuum valve attached to the back of the tachometer, the wiper door over-ride valve under the steering column, the wiper door safety vacuum valve located in the wiper cavity below the windshield, and the wiper door control valve located on the driver's side firewall. If there is a slow leak in any of these valves or the hoses, then the vacuum is lost over time and when the engine starts up the door is driven to open. As soon of the vacuum is re-established in the control side the control valve directs the door to close.

Remove the vacuum hose from the top of the wiper door control valve on the fire wall and apply a vacuum (with all valves "OFF"). You'll also need to identify the vacuum line going to the solonoid valve on the back of the tach and remove and plug it. The vacuum should hold. If it doesn't find the leak(s).

Good luck Mr. Phelps.

Andy

 

Yes to what Andy said. There is a slow leak in your vacuum system somewhere. Default position for your wiper door is OPEN so if insufficient vacuum it will open. When vacuum builds sufficiently, door closes. Some people when they start their car headlights open and close as well. Same problem.

If you need vacuum system diagram or anything, I can post it. Just send me a PM. Do you have BB or SB car?

Doug

 

I got a couple of requests tonight so will post diagram with explanation tomorrow. I'm not a vacuum guru but I have just gone through my whole system so I know a little more than I did before. Hopefully it will be helpful.

Doug

 

Not sure how to post but I have a diagram I created that covers a 1969 system. Send me your email if you'd like a copy.

Andy

 

The tool that is very helpful for the troubleshooting work is a vacuum hand pump with a gauge and a short piece of vacuum hose.

Any manual you read tells you to check vacuum on the line coming off the top of the motor while the motor is running...before the checkvalve filter is a good spot. That tells you the nominal vacuum for the system. If you get to a point where it is significantly lower, you are on the trail of the leak you are looking for.



This is the diagram for a 70-72. I know the pic is a little hard to read, has been handled a few times before I did the PDF file but I will walk you through it.

For 70-72 at least the default condition for wiper door and headlights is open. Makes sense. If systems fail, you would want lights up and wiper door open. Wasn't true on 68 I don't believe and I don't know if it was corrected in 69 or not. There was a change in 69 mid year.

Start with the vacuum coming off the block (hex symbol). With motor running, see what the vacuum is at that point. You could call that the baseline vacuum level for the system.

First you come to a filter called the checkvalve filter. My car didn't have one when I did this work so I bought one for about 8 bucks. Then a vacuum check valve. Best way to check this is to take it off and blow in it in both directions. One direction air will move smoothly, the other way it should not. If it passes air in both directions, you need to replace it. 17 bucks. Mine was dead. From there the vacuum line splits, one line goes to the vacuum reservoir which lives inside the left fender. The other line goes through the firewall to the vacuum switches under the dash. We will come back to them.

The wiper door and each of the headlights have 2 things in common...an activator relay valve (essentially a vacuum switch) and a vacuum activator which has a diaphram inside which does the work. The relay valves for the headlights are near the headlights. The relay valve for the wiper door on my 71 is actually on the right fender, not on the left side of the car as shown in this diagram. It may have been moved, I don't know. The control line for the relay valve is the vacuum line going into the head of it. System vacuum goes into the middle of 3 ports on the stem, the outside ports go to each side of the activator assembly. You can test the activators by pulling the lines one at a time from either side (with motor off) and pulling a vacuum. One way will open the door/headlight, the other will close it. If the vacuum doesn't hold, the actuator may need to be replaced or there may be a leak on the other side of it. Mine didn't move at all for the wiper door. Replace it (100 bucks I'm afraid) and it worked fine. Check with your friends who took off their wiper doors and put on long high rise hoods. They may have kept the vacuum parts that you can reuse.

Wiper door default mode is open. What can cause it to close is vacuum from the system as long as the wiper door safety valve is depressed (the wipers are parked). WDSV s a small vacuum switch right near the passenger side wiper motor and the vacuum actuator. When the wipers are in the parked position and there's vacuum on the system, the switch will allow the door to close.

One of the leads on the safety switch is supposed to be open...releases vacuum from the switch when the wipers are moving from operating to parked position and back.

If you know logic statements this will help:

What keeps the door open is either the safety valve isn't depressed, OR the manual wiper door switch is pulled OR the wiper switch is on or there is insufficient vacuum in the entire system. What closes it is when you have sufficient vacuum and wipers are off AND wiper safety valve is activated AND manual wiper door plunger is in off position.

If you suspect leaks as you trace through the system, pull a lead, pull a vacuum on one side of the line and see if it holds. You can test the leads that go through the firewall by pulling a vacuum and opening and closing the underdash switches. Essentially you walk through the system...yup vacuum here, yup got it there...until you find a spot where it drops.

The aforementioned wiper door rising up on startup and possible 1 or 2 headlights as well is fairly common, particularly I'm finding on BB cars. One should be able to get several ups and downs on the headlights and the wiper door before releasing all the vacuum from the reservoir. Not so in my case quite yet. I am still looking. You could have a cracked reservoir but it isn't likely. There is a vacuum relay high up under the dash on the drivers side which switches when the headlight switch is turned on. It may need replacing. To reach it you must take off the 6x6 plate at the forward most point of the center console on the drivers side. Isn't fun but you can reach it.

If your vacuum lines look a bit long in the tooth, you may want to replace the entire set. I recommend you replace the lines one at a time (they are color coded) so you don't have to start from scratch.

I hope this helped a little. I have another diagram in the other garage that I will bring in tomorrow and see if that sheds some light. As one person said it, you may have bigger fish to fry, but it is possible to get all the vacuum leaks out of the system. Bottom line is keep going until you find the culprit. Our cars are going on 40 years old and stuff just wears out, cracks and gets dirty.

Holler if you have more questions. Hope this was a help.


Doug

 

check your vacuum tank. isolate it from the system and put a small amount of pressure on it (3lbs +or-) and see if it holds pressure or vacuum.
i found a crack in my tank that buba had tried to solder and leaked. i had replaced all the hoses and the system seemed tight.... i thought.
i have chased headlight, wiper door problums and a surge in engine idle for a year...
what snowman said about the system is true, 40 years and getting older!
good luck!

 

I don't have any problems with my system but if I pull the vac source hose from the manifold and use my MityVac it dosen't even move the needle on the guage. Is this normal? I just replaced all the hoses but did them one at a time and like I said my headlights and wiper door work just fine. My check valve is good. Maybe a leaky vac tank?

 

is the MityVac a hand pump?
the system is to big for a hand pump....
i started to fix the cracks in my tank and as i cleaned i found more cracks than BUBA can solder....
so i went to Summit for a new tank....not correct but no cracks! ($69)

 

Yes mityvac is a handpump. I do have a venturi that I can hook up to my compressor. I might try that. I am chasing an erratic idle problem and think it's due to a vac leak. My carb connections are good and now I am looking a the headlight/wiper door vacu system as the source of my problem. My erratic idle is very small. Sometimes I idle at 700rpm and sometimes 900rpm.

BTW - as far as the original poster I know you said you changed the wiper door solenoid but my door would do almost the same thing. On startup it would pop open then close. This happens when dirt gets into the solenoid and keeps the needle valve seat inside of it closing and causes a small leak. I had a link for what to do to rebuild it but cannot find it. I'll look a little harder for it.

 

On the subject, [1968] the door actuator, I can blow ito either end and the shaft moves but not on the car with a hand pump or the engine running. Do I have something open. I cant get the lites to work up or down either. Is the actuator good if I can blow into it and shaft moves both ways?

 

Here is the link for the wiper door solenoid rebuild.
http://www.71corvette.com/wiper.html

Wally - do you hear any leaks while testing? It may be able to move the rod when disconnected but might not have enough "power" when trying under load.

 

Thanks for the replies, Snowman, thanks for the diagram, that will help a lot of folks here. I do have a leak in the wiper side, somewhere behind the dash or the wiper valve under the wiper arm. When I run manifold vacuum to the top connection on the wiper relay on the wheel well the door stays closed at start up and works very quickly when I pull the hose off and hook it back up. My next step will be to isolate the wiper valve under the wiper arm. I also think my tank has a small leak.

 

No leaks that I can hear. The exhaust is so loud it would be impossible. I did get the lites to start to open a few days ago before I fixed the door mechanism. I got them to go down without the engine running with a vacuum pump. Logically I figured I could get the wiper door to operate the same way. Could I get the actuator to move by air pressure or will I blow something else inside the can.

That was a interesting link about the switch on the tach. Damn I hate to try to get in there, positively no room. And it mentions, clean it and the door works. There are hoses on it too I suppose. Oh well,

i`;ll look at it tomorrow,
and thank you very much

 

I'd check to see if the hoses are connected to the proper ports on both the switch that the wiper arm contacts and also the wiper door solenoid behind the tach. Both have a connection that has nothing connected to it. The wiper switch does have a short rubber hose that goes through the firewall but it doesn't go anywhere. It's to bleed air off. Same with the solenoid.

Sounds like you may have faulty vacuum relays. '68's have a relays for both headlight buckets don't they? If they do a good way to troubleshoot them is to "T" both buckets to one relay and see if they work good. If they don't then switch relays and see if they do work good. If not both relays are bad. I'm not sure you want to pressurize the system. Like you said you might blow something.

 

Wyatt,

I just bought my 71 BB Vert about 6 weeks ago. Wiper door didn't open at all. Now it works when requested but on my car when I start it wiper door opens and both headlights go up then headlights down then wiper door down like clockwork. I am going to check the vacuum tank next. Have all new hoses and have proven everything else in the system.

I'll let you now what I find out.

 

If you guys are interested, this is a pretty good troubleshooting guide.
Better than I have been able to offer you here.

http://www.vettevacuum.com/troubleshooting_guide.htm

 

Here is a good thread which addresses our problem exactly. Good suggestions in there for us "open and close" guys.

http://forums.corvetteforum.com/show....php?t=2003584