Just replaced both headlight relays, hoses, check valve, filter and an actuator seal that was completely shot. Referring to the Willcox YouTube video, I'm able to open and close both actuators with a mighty-vac as in the vid. But when I draw each down to 20inHg, they drift back to 15inHg in about 30 seconds. Obviously a small leak in each diaphragm, but what does a new one do? Would a new actuator hold at 20inHg for let's say 24 hours?

 

If it were a new GM actuator it should. I wouldn't trust a new Chinese actuator at all.

Have you checked your checker (Mityvac)? You may have a leaking seal in the Mityvac if both sides leak down at the same rate. Very common. Connect a length of blocked hose and pump it down. It should hold vacuum on it's own.

In my opinion, the only important reading to test the viability of an actuator is to pump down the rear (facing driver) vacuum port and observe the reading over a length of time. The front seal can always be rebuilt to reseal it.

 

Wanted to close on this thread so the next guy with headlight problems will know what happened.

MightyVac held vacuum but the vinyl connector hose I was using did not. Made a fresh cut at each end. Pass. side holds 20 in. Hg steady for 10 minutes. Driver side still drifts indicating a very small diaphragm leak. Bottom line is both headlight doors now open almost simultaneously and close at exactly the same time. Doors will close using reserve vacuum after shutting off the engine which never happened before. Extremely satisfied.

Got a terrific message from Alan 71 which is not showing up here. Wanted to pass it along because he goes into the theory of what is not happening when there's a problem. Much better approach than replacing expensive parts and hoping the problem is fixed. After reading, I got over the small diaphragm leak real fast. Here it is--

>>>>>>>>>>>Hi c,
Even when new there may have been cars in which the system had slow leaks…. but the driver wouldn't know it.
This is because of 2 reasons….
First, the system's relays and actuators are designed to REMAIN in the position they are if the vacuum is lost.
Second, each time the engine is started the small hose 'control' side of the system gains full vacuum BEFORE the large hose 'servo' side of system gains full vacuum.
Thus the doors stay where they are at start up.
The 'winking' headlights and 'dancing' wiper door people experience is because the 'servo' side receives full vacuum before the 'control' side is able to hold the doors where they are.
There should be enough vacuum stored in the reservoir to open and close the doors at least once with the engine shut off.
Right now the system on my 71 retains enough vacuum overnight to open the doors once, but not to shut them.
Regards,
Alan>>>>>>>>>>>>>>>>>>>>>>>