Brake warning light on all of the time , 69 SS,front disc, rear drums

[Randy Shanks]

I have just finished installing new brake pads and shoes, new wheel cyls, rebuilt the single piston calipers, and new master cyl.
The front brakes are working fine, the rear brakes are not.
I am pretty sure we bled the brakes properly.
The brake warning light on the dash comes on as soon as I turn the key on. Does no go off.
I am trying to figure out if the switch/dist block under the master cyl is bad. Can this be taken apart and cleaned, or does it just need to be replaced.
The only procedure to test the switch I could find in the Service manual was to open a rear bleeder and see if the light comes on.
I can't find any method to test or clean the switch.
Also how does one test the proportioning valve and the hold off valve on the frame.
Just replacing all of these parts gets pretty expensive.
Any help would be appreciated
Randy

[z28z11]

Look in the technical articles section of Muscle Car Research - I think you can find the solution to your problems. Tuning up the distribution block and metering valve is not too difficult or expensive. The site will also give you a good understanding of what causes what (a lot of us have been through this before).

https://www.musclecarresearch.com/

This, in particular, is the one you should be looking for -

https://www.musclecarresearch.com/gm-pd-valve-rebuild

Regards,
Steve

[Randy Shanks]

Thanks Steve.
This is exactly the info I need
Randy

[Randy Shanks]

If I unplug the wire from the switch under the MC, would that shut off the light on the dash. If it does not shut off the problem is either a grounded circuit of bad switch at parking brake lever.
Am I on the right track here or not.
Any info would be appreciated.
Randy

[Mike S]

  If that block is indeed the cause of the 'brake' light to illuminate, then yes, removing the wire should cause the lamp to go off.
That light is illuminated either from the parking brake switch or the distribution block under the MC. If both wires are off and the light is still on then something is grounding that lamp. Did you remove the wire from the parking brake switch too?
  Do the brakes feel fine otherwise?

Mike

[Randy Shanks]

Mike,
I will try that tomorrow. The front brakes work good, the rear do not lock the wheel.
If the plunger in the block is pushed completely to the rear would that restrict the flow to the rear brakes?
When I brought car from storage the rear MC reservoir was dry and had a lot of fine rusty residue in it.
I replaced the MC with new one but have not done anything to the block or valves.
I also rebuilt the calipers and new pads and new rear shoes and wheel cyl.
Bled the brakes and have a good hard pedal but the rear brakes do not work, flow seemed restricted some when bleeding rear brakes.
Probably should order rebuild kits from Muscle Car Research for the block and two valves.
Very frustrating.
Thanks for your help.
Randy

[Mike S]

Hi Randy,
   It sounds like you had air sitting in the system for a while so there may be some crud in the lines somewhere.
Check to see if you have a proportioning valve mounted on the drivers side frame rail. If you have one it should be near the drivers door and has a brass body with a line in and a line out to the rear brakes. That valve can prevent fluid to the rear if it is filled with crud and the piston stuck.
 I don't think that the pressure differential block would prevent fluid from going to the rear even when activated. The way the piston works is it will move to either direction depending on which half of the braking system is failing and stop moving when the center relief of that piston body hits the center terminal 'tit'. And if it were locked to one side I would expect the brake light in the dash cluster to be illuminated.
  Another possibility is the coupling hose that connects the brake line, that travels to the back, to the brass junction block that connects to the brake lines running along the axle housing. Sometimes when brake hoses fail, it develops a one-way blockage internally thereby allowing fluid in one direction and blocking it the other way.

Mike

[KurtS]

http://www.camaros.org/brakevalve.shtml#mv
"If the brakes are bled with a pressure bleeder that develops less than 30 psi, the plunger at the rear of the metering valve must be depressed in order to hold the valve open so it allows fluid to flow to the front calipers."

[Randy Shanks]

Thanks KurtS for your response.
I started by vacuum bleeding ( with MityMite )  the MC, then the brakes.
Followed by manual bleeding the old fashion way.
I have since unplugged the parking brake switch which shut the warning light off. When I press the brakes it comes on. It goes off on release of pedal.
I am going to try to re-center the plunger in the dist. block and re-bleed the brakes again.
I have a good hard pedal so I don't think I still have air in the lines.
Maybe this will fix it.
fI that doesn't work I will rebuild the proportioning valve.
Thanks

[Randy Shanks]

Update;
now no brake warning light when I press brake pedal with key on but not running. Good solid pedal.
However when I start the engine and press the pedal I get a light, the booster seems to be working but I just don't know what to check next.
Randy

[69Z28-RS]

Seems the problem lies between the booster or the engine vacuum supplied to the booster...?