After cleaning the car for a show a few days ago, when I started the car the morning of the show, the wiper door opened and I couldn't get it closed using the vacuum over-ride switch. Some quick testing showed I had no vacuum to the control side of the vacuum relay valve. I got the door closed for the show by reversing the large hoses on the vacuum relay valve.

I have found the rubber L that goes onto the vacuum over-ride switch is a loose fit on my replacement over-ride switch. The studs the L fits on is 1mm larger diameter on the original over-ride (broke off one stud) than the replacement. (If the vendors are going to make these replacement parts, why don't they make the correctly???)

Anyway, using a mity-vac and a vacuum gauge, I have determined the red vacuum hose from the over-ride switch to the diaphragm side of the vacuum relay valve. This tells me the interlock valve and hoses above are good.

I DO NOT have good vacuum from the small hose side of the check valve to the over-ride switch. The only component in that part of the circuit is the vacuum control solenoid on the back of the tach. At this point I should mention that the headlights open and close properly, so from the check valve to the Tee is good.

My question how to access to the vacuum control solenoid. I am leaning toward removing the trim around the windshield and removing the top of the dash. I have done this before to replace the defrost defuser that had partially melted, so I know I can do this without damaging anything. I do not want to remove the dash to gain access to the back of the tach if at all possible.

Thanks for any help!

 

Hi Pete,
I don't think it's a good idea to continue testing your luck on getting the dash top pad in and out without cracking it in the center or at the ends.
I'd take the driver's seat out so I could lay on my back on the floor with my legs in the rear compartment. From that position you can see and have pretty easy access to the switch on the back of the tach.
Good Luck!
Regards,
Alan

 

If you have good vacuum to the headlights, but not to the wiper stuff, the problem is most likely a leaky check valve (on one side of it). Remove it, check its ability to seal [note: put finger over one of the outlets of the check valve, then use Mity-Vac to suck on the other outlet. It should seal. Then, swap Mity-Vac and your finger to check the other.

 

Alan, Thanks for the reply. I will do as you recommend if it comes to that.

7T1, good idea! I'll do that before digging into the back of the dash.

Many thanks, I'll let you know the final fix


Pete

 

Thanks for the tip Alan. I didn't realize how easy it is to remove the seat and lay on my back to gain access to the vacuum control solenoid. I tested the solenoid by with my mity-vac and vacuum gauge, operating the solenoid by turning the wiper control on and off (with the override switch OFF). The 43 year old solenoid still works like it should, and I saved a ton of work by not removing the top of the dash. Nice picture Alan!


My check valve tested OK on both sides when I tried your test. I did that before attacking the vacuum control solenoid because it is so easy to access.

I kept testing after the above two tests were good and found the wiper arm vacuum switch is failing. If I compress it very hard, it passes vacuum, but the top part that contacts the wiper arm is bending and cracking, so I will replace it instead of trying to readjust it. Right now I have a short piece of plastic tubing connecting the red and white hoses together, bypassing this valve. The wiper door and headlights all go up and down as they should now so I know I'm on the right path here.

This vacuum control switch is a five year old replacement. The original lasted ~37 years before failing. They don't make 'em like they used to.


Pete