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Brake Story

KPumroy

Member
Local time
7:27 AM
Joined
Jan 16, 2023
Messages
14
Reaction score
22
Location
South Carolina
So continuing the brake saga with my 1968 Charger. I had recently reworked the rear drum brakes as they were sticking and grabbing. When I had my car transported south the driver used the parking brake which seized the rear brakes up. This got me working on the rear brakes which is another story. This story is about the front disc brake conversion I had done about 20 years ago. I had a shop install a front disc brake kit with power booster, new master cylinder and combination valve. I was never impressed with the feel of of the brakes and know I know why. While working on my rear drums I cut the parking brake cable, I know I have already caught flack for that. But, I noticed there was no brake light warning coming on on the dash. I was going to disconnect the switch at the parking brake lever arm so the light wouldn't come on but there was no light. Seems someone had pulled the light bulb out of the dash and the bulb was on but illuminating an empty void behind the dash. So the brake warning light was on even though I had disconnected the parking brake switch. So next I checked the switch at the brake combination valve and guess what, there was continuity at the switch. I pulled the switch and looked into the valve and the shuttle valve had closed off the rear brake circuit. Looked online and some had suggested using a little pick tool to reset the shuttle valve. That was unsuccessful. So I replaced the brake light warning bulb in the dash and started the car, pumped the brakes up then firmly pressed the brake pedal, very firmly. I heard a little click and the brake light went off. The valve had reset! I then went around and bled the brakes with a vacuum bleeder. Wow what a difference! The brakes feel great and the car stops on a dime. So I surmise 20 years ago the mechanic didn't use the little tool that you are supposed to use to lock that shuttle valve open while pressure bleeding the brakes and for 20 years I have had little or no rear braking. The sad part is that he had artfully hidden the brake light warning bulb so I had no idea. Hopefully this will help others as those combination valves are a commonly misunderstood part of the brake system.
 
Question:
Did the brakes actually bleed correctly before? In other words....if fluid made it to the rear circuit and was flowing through the bleeder screws, I wonder if maybe the pressure and flow were just below acceptable levels and once the proportioning valve reset, the bias was finally in spec?
I'm no expert...I'm guessing here too. I've had excellent results with disc/drum setups and trouble with my 4 wheel disc arrangement.
 
Question:
Did the brakes actually bleed correctly before? In other words....if fluid made it to the rear circuit and was flowing through the bleeder screws, I wonder if maybe the pressure and flow were just below acceptable levels and once the proportioning valve reset, the bias was finally in spec?
I'm no expert...I'm guessing here too. I've had excellent results with disc/drum setups and trouble with my 4 wheel disc arrangement.
I don't know because I had never tried to bleed them before. Yeah they feel great now so the bias is working as intended. Those combination valves for front disc/ rear drum have a metering valve for the front brakes that I think you are supposed to remove for a 4 way disc system. But am am no expert either.
 
Question:
Did the brakes actually bleed correctly before? In other words....if fluid made it to the rear circuit and was flowing through the bleeder screws, I wonder if maybe the pressure and flow were just below acceptable levels and once the proportioning valve reset, the bias was finally in spec?
I'm no expert...I'm guessing here too. I've had excellent results with disc/drum setups and trouble with my 4 wheel disc arrangement.
I found this video to be very helpful.
 
I don't know because I had never tried to bleed them before. Yeah they feel great now so the bias is working as intended. Those combination valves for front disc/ rear drum have a metering valve for the front brakes that I think you are supposed to remove for a 4 way disc system. But am am no expert either.
A four disc system still requires a
proportioning valve. To prevent nose
dive under hard braking, the rear must
come into play, first, thus "holding
back" the sudden transfer of weight
from rear to front. Too much transfer
results in rear braking inefficiency.
(such action lifts the load off the rear
tires and transfers it to the front),
refered to as brake bias. This force
is multiplied if the springs and shocks
both front and rear are weak or worn,
or are of the incorrect rate of
frequency. ie...too soft a spring.
As per the attached pic, the
proportioning valve does not have
to be installed way back at the rear.
It can be installed within easy reach
to dial it in. (Note the valve below
the booster).
I have 2lb residual check valves
installed on each circuit to keep
the disc brake pads from backing
away from the rotors. My old hot
rod stops straight, level, and true.




20211227_151541_HDR.jpg
 
Last edited:
So continuing the brake saga with my 1968 Charger. I had recently reworked the rear drum brakes as they were sticking and grabbing. When I had my car transported south the driver used the parking brake which seized the rear brakes up. This got me working on the rear brakes which is another story. This story is about the front disc brake conversion I had done about 20 years ago. I had a shop install a front disc brake kit with power booster, new master cylinder and combination valve. I was never impressed with the feel of of the brakes and know I know why. While working on my rear drums I cut the parking brake cable, I know I have already caught flack for that. But, I noticed there was no brake light warning coming on on the dash. I was going to disconnect the switch at the parking brake lever arm so the light wouldn't come on but there was no light. Seems someone had pulled the light bulb out of the dash and the bulb was on but illuminating an empty void behind the dash. So the brake warning light was on even though I had disconnected the parking brake switch. So next I checked the switch at the brake combination valve and guess what, there was continuity at the switch. I pulled the switch and looked into the valve and the shuttle valve had closed off the rear brake circuit. Looked online and some had suggested using a little pick tool to reset the shuttle valve. That was unsuccessful. So I replaced the brake light warning bulb in the dash and started the car, pumped the brakes up then firmly pressed the brake pedal, very firmly. I heard a little click and the brake light went off. The valve had reset! I then went around and bled the brakes with a vacuum bleeder. Wow what a difference! The brakes feel great and the car stops on a dime. So I surmise 20 years ago the mechanic didn't use the little tool that you are supposed to use to lock that shuttle valve open while pressure bleeding the brakes and for 20 years I have had little or no rear braking. The sad part is that he had artfully hidden the brake light warning bulb so I had no idea. Hopefully this will help others as those combination valves are a commonly misunderstood part of the brake system.
I just came across your "brake story" and I am glad I did. I have been struggling with my brakes bleeding correctly on my 67 Charger with Bendix Disc up front and drums on the rear. I'm going to check this out and see if I get better results.
 
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