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Getting the dash brake warning light to go out on a 67 involves bleeding the brakes as per the instructions below. On a 70-73, you only have to depress the brake, no bleeding (see instructions below). Can the Pressure Differential Valve on a 70-73 be put into a 67 to avoid this in the future?



ADJUSTMENTS




1967-69 Models


See Figure 1



Fig. Fig. 1: Cross-section of the pressure differential warning valve


To centralize the valve:
  1. Switch the ignition ON. Have an assistant apply pressure to the brake pedal.
  2. Loosen the bleeder screw at the opposite side of the brake system that was affected or repaired last.
  3. Press the brake pedal slowly until the valve is centralized and the light goes out. Retighten the wheel cylinder bleeder screw.
  4. Check the brake fluid level and brake pedal height and firmness. Road-test the car.
1970-73 Models

To centralize the valve:
  1. Turn the ignition to ACC or ON.
  2. Check the fluid level in the master cylinder reservoirs. Fill up to within <SUP>1</SUP> / <SUB>4</SUB> inch of the top.
  3. Depress the brake pedal firmly and the valve will centralize itself causing the brake warning light to go out.
  4. Turn the ignition OFF.
  5. Prior to driving the vehicle, check the operation of the brakes and obtain a firm pedal.
 

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So, your car has factory disc brakes? I don't think you have to completely bleed the system, just take enough pressure off to let the pintle get re-centered.
However, a later model power disc brake proportioning valve serves the same purpose. However, you will need to bleed the brakes after you change it, so I don't really think you are gaining much from the swap...
 

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I like the older way because if you have a hydraulic failure the brake light will stay on until the problem is fixed. Example: Driver 1 has hydraulic failure. Limps car home but does not tell other drivers about the problem. Driver 2 gets in the car and starts the car and see's the brake light is on so does not attempt to drive the car. The newer self centering valve would not pre warn driver 2 or the original driver if they were a dumas aka the light is out now so it must be OK.

Bill
 

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Kinda off subject but does anyone know how the brake warning light switch is wired?
I am in the process of rewiring my 68 xr7 and am a bit confused with this part. I have a wiring diagram but the print is so small. I know it is wired through the ignition switch on the cranking side, and this is for checking to see if the light in the dash is working. After that I am not sure.
 
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