Topic: Proportioning valve - working?
in Forum: C3 Engines, Driveline and Handling
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Does anyone know how to tell if a hydraulic brake proportioning valve is still operating correctly?? My non-power brakes seem to be operating just fine but the "brake" light on the dash glows dimly. I replaced the wiring in that circuit so I know that it and the parking brake switch are fine.
Also, where can I get a good price on one if I do need to replace it? Ecklers wants $95 for something they call "Proportioning valve service" (rebuilding?).

Also, where can I get a good price on one if I do need to replace it? Ecklers wants $95 for something they call "Proportioning valve service" (rebuilding?).

'69 350/350 conv.
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Toledo, OH - USA
Joined: 9/4/2002
Posts: 147
Vette(s): 1976 Stingray, L48 auto Buckskin/Buckskin Leather originally. Numbers matching.
Generally, if the proportioning valve goes bad, you will end up with rear wheel lockup. Its job is to limit the amount of fluid pressure to the rear wheels. On light pdeal pressure, nearly equal pressure is transmitted to front and rear. On heavier stopping, the proportioning valve reduces the amount of pressure sent to the rear, just enough to prevent skidding.
'76 L48 Auto
Project
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I replaced my valve a couple months ago. I have replaced everything in the brake system, and the valve was all that was left. It was not the problem in my case.
In the maintenace books, it states, to reset the switch in the valve, to push "quickly" on the brake pedal, (this will reset it back to the center position). Let me know if this helps.
bill0830@yahoo.com
In the maintenace books, it states, to reset the switch in the valve, to push "quickly" on the brake pedal, (this will reset it back to the center position). Let me know if this helps.
bill0830@yahoo.com

1975/L48/Coupe/4 Speed(1 of 1057)/Headers/true duals/aluminum intake/holley 750/MSD ignition/roller rockers/
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Hi
Even that this valve is called a proportioning valve, it isn't.
It just measures the pressure going to the front versus the aft brakes to bring the red brake light on in case of irregularities.
The higher braking force to the front is done only by the caliper piston diameter being much bigger than the aft once.
The braking pressure( not force ) to the front or rear should be the same.
This is so at least on early C3.
If the light comes on, you most probably have air in the aft brake system. Needs to be bled and if it reoccures, you have rear wheel run out pumping air into the brakes.
Easy fix is to install O-ring caliper pistons.
More difficult and expensive way is to replace rear wheel bearings and true the discs.
Have fun. Gunther
Even that this valve is called a proportioning valve, it isn't.
It just measures the pressure going to the front versus the aft brakes to bring the red brake light on in case of irregularities.
The higher braking force to the front is done only by the caliper piston diameter being much bigger than the aft once.
The braking pressure( not force ) to the front or rear should be the same.
This is so at least on early C3.
If the light comes on, you most probably have air in the aft brake system. Needs to be bled and if it reoccures, you have rear wheel run out pumping air into the brakes.
Easy fix is to install O-ring caliper pistons.
More difficult and expensive way is to replace rear wheel bearings and true the discs.
Have fun. Gunther

Hi Gunther,
Thanks for your input, I just assumed that it was a proportioning valve because every catalog I have ever seen refers to it in that way. Two things I feel compelled to mention here;
1. The light does not actually light, it just glows dimly. It will brighten considerably (3 times brighter) if you pull the parking brake.
2. The brake pedal is always high and firm, and it never varies depending on how long I drive, at what speeds, or how infrequently I use the brakes.
If I'm getting air bubbles then it should be most prevolent after extended high speed driving, which I haven't seen. I would think that if the system needs bleeding the pedal wouldn't be high and firm. My experience with brake lights is that they are either on or off, and glowing dimly is an indicator of a bad switch, thats why I haven't been too concerned about replacing it.
Bottom line: if its an electrical issue I don't care, but if its a brake system issue than it will be replaced.

Thanks for your input, I just assumed that it was a proportioning valve because every catalog I have ever seen refers to it in that way. Two things I feel compelled to mention here;
1. The light does not actually light, it just glows dimly. It will brighten considerably (3 times brighter) if you pull the parking brake.
2. The brake pedal is always high and firm, and it never varies depending on how long I drive, at what speeds, or how infrequently I use the brakes.
If I'm getting air bubbles then it should be most prevolent after extended high speed driving, which I haven't seen. I would think that if the system needs bleeding the pedal wouldn't be high and firm. My experience with brake lights is that they are either on or off, and glowing dimly is an indicator of a bad switch, thats why I haven't been too concerned about replacing it.
Bottom line: if its an electrical issue I don't care, but if its a brake system issue than it will be replaced.

'69 350/350 conv.
in Forum: C3 Engines, Driveline and Handling
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