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Hello everyone
Since I received my base 71, it always had the brake light on on the dash. I thought it was an electrical fault and until a few days ago I had not tried to solve the problem. The car always ran perfect.
After reading and learning in some threads on the forum, I decided to unplug the connector on the proportioning valve, the light went off. The car braked excellent and pedal was firm, but still I thought I had one of the brakes not working so I purged the system, but the light is still on. All 4 wheels brake evenly and the pedal remains firm.
Can a proportioning valve, despite the above, be blocked? Or maybe the valve itself is bad? It is new, since the car was completely restored in 2020, but I do not have contact with the previous owner to know if the light has been on since the restoration, or if it came on at some point.
If it serves as information, the light on the dash doesn't come on when I applied the parking brake, but I think that's another problem.
What do you advise me?
If you are talking your '71 I believe you have a distribution block which only serves to let you know if there is a hydraulic fault in the brake system.
Proportioning is already built into the brake system by the sizing of the caliper pistons to get the right balance (proportion) of braking force between front and back.
The distribution block senses difference in pressure between front and back and activates the brake light via shuttle valve built into the distribution block when there is a fault
To make the light go out and recenter the shuttle piston you need to "crack" a front or rear brake line while brake pressure is applied - a bit of a trial and error process.
Good luck !
The above could work if needed.
Even easier is the service manual recommended method:
Stab the brakes HARD! a few times. That should center / reset the valve / light.
There is a $7 tool you can buy on Amazon to prevent the valve from moving in the first place while you bleed the brakes.
Pifo,
Early C3s had distribution blocks.
Later models, not sure exact yr, changed to Proportioning Valves.
The wire going to the switch at the unit is a GRD wire.
I suspect that connection just needs a thorough cleaning of grease & road grime to work correctly.
If you are talking your '71 I believe you have a distribution block which only serves to let you know if there is a hydraulic fault in the brake system.
Proportioning is already built into the brake system by the sizing of the caliper pistons to get the right balance (proportion) of braking force between front and back.
The distribution block senses difference in pressure between front and back and activates the brake light via shuttle valve built into the distribution block when there is a fault
To make the light go out and recenter the shuttle piston you need to "crack" a front or rear brake line while brake pressure is applied - a bit of a trial and error process.
Good luck !
Pifo,
Early C3s had distribution blocks.
Later models, not sure exact yr, changed to Proportioning Valves.
The wire going to the switch at the unit is a GRD wire.
I suspect that connection just needs a thorough cleaning of grease & road grime to work correctly.
You got it bass akwards
It's a ground wire so if the connection wasn't "good" then the light would NOT come on !
The above could work if needed.
Even easier is the service manual recommended method:
Stab the brakes HARD! a few times. That should center / reset the valve / light. REALLY ??
There is a $7 tool you can buy on Amazon to prevent the valve from moving in the first place while you bleed the brakes.
I have used both. Both work. So does pulling the switch and using a pic to center the little shuttle valve.
The screw in tool eliminates the whole problem.
A handy tool for Corvettes, as you know we bleed the brakes a lot.
Also fits other GM musclecars of that era.
As some one mentioned, somewhere in the mid/late 70s, the block/switch in the vette changed to a real pressure proportioning valve.
Unless you had an L88 which came with a separate adjustable pressure proportioning valve. I put on of those on my Z28 back in the late 70s.
Last edited by leigh1322; Dec 21, 2024 at 05:11 PM.
Thanks everyone for the advice.
This morning with the help of my wife I first bled a front caliper, without being able to get the light to go off, the same when I bled a rear one. In both cases the DOT3 came out.
I'm going to order a tool to see if whith that I can center the valve.
Thanks again!
Thanks everyone for the advice.
This morning with the help of my wife I first bled a front caliper, without being able to get the light to go off, the same when I bled a rear one. In both cases the DOT3 came out.
I'm going to order a tool to see if whith that I can center the valve.
Thanks again!
The important headline here is that you married well!!!
Here is an internal diagram of the distribution block for a 71-72 with the "safety light" in the tripped position, with the shuttle valve shifted.
Being able to visualize the internals should help you re-center it.
Since your light is "on" and pulling the wire turns it off, the valve is tripped.
Am I stupid or does the brake indicator light also run to the parking brake lever? I am pretty sure that the brake light will illuminate for either condition. Have you removed the parking brake console to ensure the parking brake switch is connected and working?
Am I stupid or does the brake indicator light also run to the parking brake lever? I am pretty sure that the brake light will illuminate for either condition. Have you removed the parking brake console to ensure the parking brake switch is connected and working?
In my car, apparently it's not working. When I unplug the brown wire from the valve, the dashboard light goes off and if I apply the parking brake, it works but the light doesn't come on.
I have not taken apart the center console to see if the switch is connected. I thought, and perhaps I am wrong, that the light on the dash was exclusively due to the valve as it goes off when I unplug the brown wire.
I'm not very skilled with electrical issues, but could the problem be in what you mention?
Thanks everyone for the advice.
This morning with the help of my wife I first bled a front caliper, without being able to get the light to go off, the same when I bled a rear one. In both cases the DOT3 came out.
I'm going to order a tool to see if whith that I can center the valve.
Thanks again!
before you spend more money sit in the drivers seat start the car and and bang the brake hard a few times while sliding your foot off the pedal
From: Loud, Raw and Dangerous 1968 327 4S in Southern California
Originally Posted by Eliredandblack
Am I stupid or does the brake indicator light also run to the parking brake lever? I am pretty sure that the brake light will illuminate for either condition. Have you removed the parking brake console to ensure the parking brake switch is connected and working?
Took a look at the schematic for my 1968 car and it does look like the brake failure warning switch and the parking brake warning switch are in parallel on my year. If ether one connects to ground the parking brake indicator light comes on. This is thru the fuse block +12V Ign "Gauges" fuse circuit.
So yes maybe the light is on because of an issue with the parking brake part...switch is pressed on or internally shorted or a miswire somewhere. However if unplugging the brown wire makes the light go off likely not.
Last edited by Redvette2; Dec 22, 2024 at 01:06 PM.
Reason: Kan't spel
I have a line lock on my front wheels. Every time I use it the valve gets out of center and leaves the brake light on after using it. I can confirm that simply stabbing the brake pedal hard and releasing will recenter the valve.
What would you call this gizmo if you were to search Amazon for it?
TIA.
Originally Posted by leigh1322
The above could work if needed.
Even easier is the service manual recommended method:
Stab the brakes HARD! a few times. That should center / reset the valve / light.
There is a $7 tool you can buy on Amazon to prevent the valve from moving in the first place while you bleed the brakes.
Hope that little tool works, as I see it the little tool keeps piston from moving too far BEFORE it gets stuck when bleeding brakes, but if it is already stuck one way or the other will it move the piston back to center?? Me thinks it is time to replace valve.
Proportioning valve advice.
