vacuum relay leak between ports - what's tolerable?

[Randall K.]

How much leakage to ambient air is toelrable between the ports on a headlight/wiper vacuum relay? I have two in my car that will lose vacuum slowly when tested with a hand vacuum pump - say about 1 inch Hg per 15 seconds. There are no leaks from the actuator itself - it holds a steady vacuum.

Thanks
Randy

[Jack H.]

Re: vacuum relay leak between ports - what's tolerable?

The general technique for vac troubleshooting is to step though the system point by point measuring vac pressure as you go with the ultimate reference being the head end pressure at the intake manifold. At least one troubleshooting reference guide advises that a pressure drop of > 2 psi across a given vac component flags undesirable vac integrity characteristics...

[Michael W.]

Re: vacuum relay leak between ports - what's tolerable?

If tolerable means to enable the system to work, I'm not too sure how much of a leak is too much. If you mean what was the original design standard, the answer is no leakage permitted.

It's very common to see a high leakage rate on >25 year old unrestored relays.

[Terry M.]

Re: vacuum relay leak between ports - what's tolerable?

I know one former NCRS member (RIP) who got the vacuum system on his 1971 to hold vacuum for several days. He went to extra ordinary lengths to do so. I saw it with my own eyes, so it can be done. It just depends on how much work you want to go through. He did a few things that were non-TFP, but you wouldn't be able to find what he modified unless he disassembled the car for you.