Vacuum Relay Test
Thread Starter
Burning Brakes
Joined: Jul 2004
Posts: 783
Likes: 38
From: Mankato Mn
Vacuum Relay Test
I'm starting to put my headlight system back in my 68. I've got a pile of vac relays (9 of them) from past projects. I've read posts here on testing and so far I haven't passed the first test. (hand pump on the small (white) port. Not one of them hold vacuum ! Can I assume they are all junk ? Or am I missing something ?
Le Mans Master
Joined: Aug 2006
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From: mount holly NC
2025 c3 ('74-'82) of the Year Finalist - Unmodified
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Safety Car
Joined: Oct 2007
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From: Seattle Area Washington
If they won't pass the first test why bother?
If the relays actuator will not hold a vacuum and if you feel like spending a little extra time removing and inspecting the inner spool or some call it the "Dog Bone" for cracks or defects it can be reused.
The spool overtime can dry out, crack and then vacuum to the headlight actuator(s) will most likely port to exhaust.
Hardest part is removing the pinched washer securing spool to actuator shaft.
And even that isn't to bad to remove.
Save Your "Dog Bones"!
If the relays actuator will not hold a vacuum and if you feel like spending a little extra time removing and inspecting the inner spool or some call it the "Dog Bone" for cracks or defects it can be reused.
The spool overtime can dry out, crack and then vacuum to the headlight actuator(s) will most likely port to exhaust.
Hardest part is removing the pinched washer securing spool to actuator shaft.
And even that isn't to bad to remove.
Save Your "Dog Bones"!
Race Director
Joined: Jul 2015
Posts: 13,082
Likes: 3,399
From: SW Florida.
not holding vac on the small hose is the diaphragm in the top of the relay. not the spools. they don't have to be perfect. vacuum there holds the headlights down. put vac pump on and watch the spool in the bottom of the relay. if spool pops up with vacuum and i holds for a minute or so, it will run your headlights. your car is running. making enough vacuum. you can pry open the lip on the vacuum can and disassemble them. do not lose the little clip on the bottom of the spool. nobody makes an e-ring that small.
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Joined: Oct 2015
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Heres some good stuff to save for the future
http://repairs.willcoxcorvette.com/1...p-for-testing/
http://repairs.willcoxcorvette.com/w...4-08032015.pdf
http://repairs.willcoxcorvette.com/w...-schematic.pdf
look this page for the vacuum flow though the realy valve and how it operates. it shows where you should feel vacuum and how to switch it. YOu need 2 vacuum sources
http://repairs.willcoxcorvette.com/1...they-function/
http://repairs.willcoxcorvette.com/w...ey-operate.pdf
http://repairs.willcoxcorvette.com/1...p-for-testing/
http://repairs.willcoxcorvette.com/w...4-08032015.pdf
http://repairs.willcoxcorvette.com/w...-schematic.pdf
look this page for the vacuum flow though the realy valve and how it operates. it shows where you should feel vacuum and how to switch it. YOu need 2 vacuum sources
http://repairs.willcoxcorvette.com/1...they-function/
http://repairs.willcoxcorvette.com/w...ey-operate.pdf
Race Director
Joined: Jul 2015
Posts: 13,082
Likes: 3,399
From: SW Florida.
you mean on the 3 big ports? 2 are always connected together. the small hose pulls the dogbone-piston-whatever up and down connecting either the top or bottom vent to the center one. and generally if it holds vac in the down position it will hold in the up position. as the same set of seals on the end of the piston do the sealing. the small vent is by itself and just raises-lowers the piston. the smile shaped hole has to be clear. open to atmosphere or the lights will go down but not up.
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