Vacuum relay valves
Thread Starter
Pro
Joined: Jul 2004
Posts: 713
Likes: 61
From: Waterford CT
Vacuum relay valves
Does anyone know if leaky C3 vacuum relay valves can be rebuilt, or do they have to be tossed and replaced? My original '71's are getting a little leaky. I took each one out and bench tested it. The two head light units leak a "little" and the wiper door unit leaks more, but not enough to cause rough idling or affect function, it just flattens the vacuum tank within a couple minutes of parking the car. Leak is out the open vented end of the spool valve and since all the parts are plastic I know it's not corrosion, just seal wear. Generic replacements that I found are in the $65 range and GM Delco units as per original are almost twice that much. Since my car is very original I would have to spring for the more expensive pieces. I'd like to hear the thoughts of the C3 corvette masses regarding vacuum relay valves.
Le Mans Master
Joined: Dec 2007
Posts: 6,422
Likes: 591
From: McHenry Illinois
, I'm interested in this too. Both mine for the headlights leak. I took them apart and the seals on the spool are worn. The diaphrams are good yet. I hate to put out another $100 for these, this car is putting me in the poor house fifty or a hundred at a time.
Last edited by '75; Mar 24, 2020 at 07:32 PM. Reason: renewed pictures
Burning Brakes
Joined: Jun 2002
Posts: 837
Likes: 3
From: Texas
Good pic of the valve Dean (lower pic). There are "cups" at each end (not shown in the pic). Get 4 o-rings 5/16" OD X 3/16" ID X 1/16" thick. Swab some black 3M weatherstrip adhesive into a cup, then press an o-ring into it and keep some pressure on it until it sets up. The idea is to flare the cups on each end of the valve so that it makes contact with the inner cylinder of the relay. Mine have help up for over 6 years now using this method.
When I reassembled my relays I also put a very thin coat of RTV on the diaphram.
Hope this helps.
When I reassembled my relays I also put a very thin coat of RTV on the diaphram.
Hope this helps.
Last edited by goinbroke; Mar 14, 2008 at 10:49 PM.
Burning Brakes
Joined: Jun 2002
Posts: 837
Likes: 3
From: Texas
Yes, I used a Q-tip to reach up into the plastic body. Seems like petrolium jelly is what I used. Also a light coat on the outside of the rubber valve. I cut some new pieces of foam for the filters as one of mine was shot and the other missing. Be sure and bench test the relays with your hand held vacuum pump after reassembly.
Le Mans Master
Joined: Dec 2007
Posts: 6,422
Likes: 591
From: McHenry Illinois
There's a small washer looking clip on the bottom end, just pried it off with a small screwdriver, then put the small screwdriver into the ports and gently moved the spool out enough to get ahold of it. Don't know if that retainer piece will stay on later, I might have to crimp something else onto the metal rod.
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Thread Starter
Pro
Joined: Jul 2004
Posts: 713
Likes: 61
From: Waterford CT
Thank you all for your input. I too didn't think I could get the spool out without opening up the crimp on the diaphragm cup and since the diaphragm is still tight I really didn't want to go hacking on that! I will try the spool release trick and get a couple o-rings for the cups.
Goinbroke, how did you reassemble? and how did you get access to the diaphragm?
Goinbroke, how did you reassemble? and how did you get access to the diaphragm?
Melting Slicks
Joined: Oct 2006
Posts: 2,417
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From: Texas
Drifting
Joined: May 2005
Posts: 1,909
Likes: 6
From: Lake Arrowhead - Georgia > 72 Base Coupe & 74 BB Roadster
OK...this hurts me to say this, but I have sprayed the insides with WD40. It's a Bubba fix, but it causes the rubber to swell and it will once again control the direction of vacuum. Sorry to admit this! I feel so cheap! I am going to bed.
Thread Starter
Pro
Joined: Jul 2004
Posts: 713
Likes: 61
From: Waterford CT
Great pics. How did you hold in the spool valve after putting it back? I haven't taken mine apart yet so I can't visualize how tough it will be to get apart and reassemble. Three day weekend coming so I hope to Git 'er done!
Burning Brakes
Joined: Jun 2002
Posts: 837
Likes: 3
From: Texas
Thank you all for your input. I too didn't think I could get the spool out without opening up the crimp on the diaphragm cup and since the diaphragm is still tight I really didn't want to go hacking on that! I will try the spool release trick and get a couple o-rings for the cups.
Goinbroke, how did you reassemble? and how did you get access to the diaphragm?
Goinbroke, how did you reassemble? and how did you get access to the diaphragm?
Le Mans Master
Joined: Dec 2007
Posts: 6,422
Likes: 591
From: McHenry Illinois
Thanks, The tiny washer in the pic with the pencil is what I pried off to get it apart. The rod has a flattened area near the end so I put the tiny washer on there and crimped it with needle nose pliers. I cycled the relay valves several times and it seems to be holding.
