TedH

Back in early 2005, I started diagnosing a stubborn wiper door and hesitant wipers on my '69 L46. First indication of problems to come was that the prior owner used the wiper door override switch to open the door before turning on the wipers... Well, first step for me in trying to solve the ills of this vacuum/electric system was to install a fresh headlight/wiper vacuum hose kit from Dr Rebuild. Then, I replaced the failed switch located under the wiper door that the wiper arm rests against... the accordion boot and moving part of the switch was complete gone, all that remained was the plastic body. Anyway, after changing both of these items, I discovered one of the key wiper door screw holes was stripped and the wiper door was not going to open unless I raised it by hand so I removed the door entirely.

Where I am today:

Headlights open and close... not a problem.

Wiper door removed... I need to get that hole re-threaded.

Wiper door actuator not operating. Only way to rotate the wiper door hinges is by hand (carefully). I need help in diagnosing the difffernet valves/actuators. I've checked a few of my 'weekend projects' and none do a very good job of saying what hoses to test at each valve (and, how to connect my vacuum pump to them to test them...).

Wipers will operate if I manually rotate the wiper door hinge assembly...

Need help from those that've successfully troubleshooted this system.

NOTE: The wiper door actuator and the wiper door relay valve appear original. I need to know how to test them to see if either has failed.

Thanks!

Thinpockets

Here is something to get you started.

http://vetteworks.tripod.com/techdocuments/Vaccum.html

Oldguard 7

Maybe this is one of the reasons GM got rid of this system for the 1973
model.

TedH

The problem with this is it describes the role of each component but I need to know how to test each vacuum component. I need instructions that tell me how to connect my vacuum pump to each of the components and the readings/behavior the components should exhibit if working/broken. I'm just not getting this type of instruction.

TedH

Totally useless information...

L Holmes

This site give a brief description of and method to test each componenet. Hope this helps. Good luck, your going to need it..

http://www.corvette-101.com/vacuum.htm

TedH

Excellent and very practical instruction. Several of the componets, namely the actuator, relay and the manual override "pull down" switch are similar between the headlight and wiper door systems.

My first test failed: With the wiper door hinges in the closed position (similar to headlamps in the closed position), I disconnected the large red stripe hose from the front of the wiper door actuator and connected the vacuum pump to the actuator fitting and applied vacuum. Needle would jump but then sit right down on the vacuum gauge. Actuator will not hold vacuum. Replacement needed...

Will advise what I find when I test the relay on the firewall and the pull down switch under the dash.

NOTE: I noted a rubber grommet loosely fitting in the nose of the wiper door actuator. Question: Can the actuator seals be rebuilt in the same manner as the headlight actuators? Sure would prefer to just replace seals if possible.

TedH

Next, tested the wiper door relay valve. Instructions say to remove all four hoses (large red, yellow, green on the bottom ports and the small white hose on port on top of the valve).

Test #1: I assumed all hoses to be removed with the exception of the following: Block off the green port and attach the vacuum pump to the yellow port. Vacuum pressure should be maintained. Result: When I pumped the vacuum pump, the pressure dropped like a rock (would not maintain a vacuum). FAIL

Test #2: (I assumed all other hoses still to be removed) Apply vacuum to the small metal port and note if the valve moves freely up towards the diaphfragm. Result: the valve would bob off its seat slightly and then settle right back to it. FAIL

Test #3: Release the vacuum at the small metal port. The valve should sharply snap toward the filter end. Result: The valve 'settles' slowly toward the filter end. FAIL

Need:

1) New wiper door relay valve

2) Either replace the wiper door actuator or get new seals/grommets for it from Dr Rebuild

TedH

OK. I repeated these tests with ALL hoses securely connected and better connections with my vacuum pump hoses:

1. Block off green port (pinched) and attach vac pump to yellow port. Apply vacuum. Vacuum pressure should be maintained. Result: FAIL. Could not generate or maintain vacuum pressure. This would prevent the holding tank from holding vacuum "... because the yellow port is always open to the vacuum storage tank". Relay should be replaced (BUT "... Failure of this test does not mean the relay will not function at all".

2. "Apply vacuum to the small metal port and note if the valve moves freely up towards the diaphragm.". I ensured all hoses were connected securely; especially the small hose where it connects to both the vacuum pump and the relay... it did not seat well against either surface on my prior test. RESULT: PASS. The valve moved freely up towards the diaphragm and would maintain vacuum until I released the vacuum.

3. "Release the vacuum at the small metal port. The valve should sharply snap toward the filter end.". RESULT: PASS. With secure connections I applied vacuum and when I released vacuum, the valve snapped back to the filter end.

4. "Apply vacuum to the small metal port. Pinch off this hose to maintain vacuum pressure and remove the vacuum pump.". Up to this point, I was PASSing this step... "Block off the red port and apply vacuum to the yellow port.". RESULT: FAIL. I could not generate a vacuum reading above zero while the vacuum pump was attached to the yellow port. However, the valve in the relay did not return to a seated position once I removed the yellow hose, attached the vacuum pump and applied vacuum.

So, it appears I have a leaky wiper door relay valve.

TedH

For now, I am going to order the Genuine GM Delco wiper door relay valve and the front grommet for my actuator... If the actuator still refuses to work, I'll drop the $170-200+ for the new actuator, some shouldered mounting bolts and plastic shims. I checked the actuator and the bellows are definitely working as I get strong air pressure from both outlets of the actuator when I operate it by hand but I get some leaking from that front grommet that has shrunk and is hardened from age... for $12 I'm going to see if the grommet is the problem. I remember repairing the grommets on my headlight actuators on the '80 L48 and I'd rather repair than replace.

Will advise once I install the replacement parts.

L Holmes

Glad the info. was of help to you. Did you use a hand pump similar to the one on the link? I have said it in the past and I will say it again. Whoever had the great idea to put these vac. systems on these cars should be kicked square in the groin.. Worst part of owning a C3 vette..

TedH

Yes, I've had a hand-operated vacuum pump for a while. Handy for troubleshooting those vacuum parts underhood. Thanks for providing this info.

L Holmes

No problem, glad I could help. I have been amazed at the wealth of tech. info Im able to get from this forum..

HamCrab87

Thanks for the info ... I recently bought a 69 L36 and am having similar issues. Had to use the override to work the wipers ... switch inop ... now the wipers won't park and door stays up. Good info from this thread to help me troubleshoot this issue.

TedH

Will post an update once I install the new relay valve and actuator grommet.

TedH

I installed the replacement wiper door relay valve and wiper door actuator seal. Had high hopes the actuator seal would cure the actuator ills but it was not to be. The actuator would rotate the hinges about .5-1" and stop; and that was if I rotated the hinges off of full open or seated/closed. So, it appears the wiper door actuator needs replacing. Cost at Dr Rebuild is approx $200... gonna have to wait until after tax season.

Corvette ED

Before you buy one do this start the car and disconnect the green hose from the canister. On the back of the intake where the vacuum hose comes off of the fitting the hose should go to a small silver valve with that end going in and two hoses out.

Disconnect the end going into the small valve and hook it up direct to the vacuum canister where the green hose was. The door should open if the canister is good. If the door opens, then unhook the red hose and put the vacuum hose from the front onto it and it should close. This will tell you if the canister is good or bad.

If the rod on the canister is out of adjustment the door will not open. Also lube all of hinges good to make it move free.

I had a problem with a 68 at work and found that somebody broke off the nipple on the green hose on the relay and it was stuck about one inch into the hose and was blocking the vacuum from going through it.

Also there is a electric/vacuum switch that mounts on the back of the tach or is hanging under the dash if a hose is off it the door won't open.

68 L71

great info all...i am currently working on my vaccuum system, headlights are working now (although rather slowly), wper door is my next issue.

Thinpockets

Got one of these?



This is one of the most useful tools you'll ever own for your Corvette. In addition to brake bleeding you can diagnose vacuum problems - both engine and vacuum systems.

It's a vacuum brake bleeder and available at most auto stores or Corvette parts sites, and it will help solve a lot of Corvette problems. Also most Corvette sites sell a vacuum system diagnostics paper that is very easy to understand.

TedH

One of the papers that provided instruction on testing the actuator said to attach a vacuum pump where the red (stripe) hose attached to the front of the actuator and apply vacuum. If the actuator is working, it should build vacuum and rotate the hinge assembly to the open position. The actuator didn't do anything and it would not take any vacuum (vacuum pump never went above 0). This was after I replaced the very loose front grommet on the actuator with one that fit very snugly.