BLEEDING BRAKES with a PROPORTIONING VALVE

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coalman

coalman

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Just changed out a dual chamber master cylinder and one 10" rear drum brake cylinder. The question I have, do you open your proportioning valve full open to bleed the rear brakes?? Thanks a bunch
 
First you need to bench bleed the master before putting it into the car or you will never get your brakes bled. Then yes open the valve wide open. Start with pass rear first then drivers rear then the fronts.
 
Fisher said:
First you need to bench bleed the master before putting it into the car or you will never get your brakes bled. Then yes open the valve wide open. Start with pass rear first then drivers rear then the fronts.
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Bled the master cylinder on the bench, aft chamber for front disc brakes bled out just fine, having trouble with the rear drums, I will open the proportioner valve full open... Thanks
 
Do you have multiple proportioning valves? on none on the front. i bought a factor disc drum one for an A body from Dr Diff for my application they bled fine.
 
Fisher said:
Do you have multiple proportioning valves? on none on the front. i bought a factor disc drum one for an A body from Dr Diff for my application they bled fine.
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Just one, inline going to the rear drums.. Thanks
 
Sounds like you have an adjustable proportioning valve. Amazing how helpful photos are when you ask questions. It is not a simple valve, but rather a spring-loaded differential pressure regulator. The knob sets the dP. You shouldn't need to adjust it to bleed the rears. If you press the pedal hard enough, it should open and flow to the rears. I'm not even sure which way the knob works. I assume that as you screw the knob cw, the rear braking gets stronger. That means it opens at a lower pressure, so wouldn't hurt to screw the knob all the way "in".
 
BillGrissom said:
Sounds like you have an adjustable proportioning valve. Amazing how helpful photos are when you ask questions. It is not a simple valve, but rather a spring-loaded differential pressure regulator. The knob sets the dP. You shouldn't need to adjust it to bleed the rears. If you press the pedal hard enough, it should open and flow to the rears. I'm not even sure which way the knob works. I assume that as you screw the knob cw, the rear braking gets stronger. That means it opens at a lower pressure, so wouldn't hurt to screw the knob all the way "in".
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Yes, it is installed under the car in the rear brake line run. Clockwise more and counter less. Thanks
 
No, you do not have to mess with the prop valve to bleed the brakes. Most OEM prop valves are not even adjustable. How would you bleed the brakes if it were all OEM? Think about it.
 
69_340_GTS said:
No, you do not have to mess with the prop valve to bleed the brakes. Most OEM prop valves are not even adjustable. How would you bleed the brakes if it were all OEM? Think about it.
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My guess is the factory setup is a given, as all would be the same. The after market discs are installed in most cars that had drums up front. That is why the adjustable prop valve, does that make sense??? Thanks
 
The factory prop valve is the same basic design, but not adjustable. It acts only upon the rear circuit, so bleeding is the same. It is buried inside the "combination valve", which provides several other functions - imbalance warning switch, front "metering valve", and distribution block. The OP is smart to use an adjustable prop valve since the factory valve was set for conditions that no longer exist. Unless someone has the same bias tires and brake pads & shoes a factory disk car shipped with, their prop valve probably isn't set optimally. You need to run skid tests in a wet parking lot to set perfectly - fronts skid just before rears.
 
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