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Author Topic: Parking Brake Strangeness  (Read 444 times)
tmathis
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« on: September 10, 2013, 07:03:32 PM »

Had to replace the parking brake PP valve to pass inspection, there was a slight leak around the "stem" the knob goes on.
The old valve was superseded back in the late 70s. This is on my 71 Eagle btw.
Besides that, it was working as it should.
Now, the new valve will release as it should but with any more than a slight application of the service brake the valve pops up and engages the parking brakes. Anyone seen this? Any ideas where to start?
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Tony Mathis
1971 Eagle
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luvrbus
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« Reply #1 on: September 10, 2013, 07:16:03 PM »

Check and be sure the replacement has a check valve you may need to install a inline check valve if not
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Live each day like it was your last,one day it will be
tmathis
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« Reply #2 on: September 10, 2013, 07:27:00 PM »

I didn't notice any kind of check valve mechanism in the old one, but that gives me a place to start.
Thanks
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Tony Mathis
1971 Eagle
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TomC
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« Reply #3 on: September 10, 2013, 09:53:36 PM »

Sounds to me that the brake pedal supply is taken off the same supply to the parking brake button. So when you push on the brake pedal, the air pressure drops enough to pop the parking brake. Look into rerouting the supply for the brake pedal, or reroute the sensing air supply for the parking brake so neither affects the other. I would not install a check valve-the parking brake has to be able to be bled off-with a check valve the pressure would remain the same even with an air pressure failure. Good Luck, TomC
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
Oonrahnjay
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« Reply #4 on: September 10, 2013, 10:48:50 PM »

  Sounds to me that the brake pedal supply is taken off the same supply to the parking brake button. So when you push on the brake pedal, the air pressure drops enough to pop the parking brake. Look into rerouting the supply for the brake pedal, or reroute the sensing air supply for the parking brake so neither affects the other. I would not install a check valve-the parking brake has to be able to be bled off-with a check valve the pressure would remain the same even with an air pressure failure. Good Luck, TomC 

      Yeah, I feed air to my push-pull switch direct off both tanks (with check valves at the tanks so if there's a leak on the compressor side of one tank, it won't "back feed" and drain both tanks - at least not immediately, giving time to get off the road).  Of course, there's a low-pressure sensor on both tanks so if one is going down, the buzzer will be squealing.
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Bruce H; Wallace (near Wilmington) NC
1976 Daimler (British) Double-Decker Bus; 34' long
6-cyl, 4-stroke, Leyland O-680 engine

(New Email -- brucebearnc@ (theGoogle gmail place) .com)
luvrbus
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« Reply #5 on: September 11, 2013, 06:17:07 AM »

Eagles had a check valve built into original PP valve check ,if he has a bad DD3 it will pop on a Eagle when you push the pedal if he has the plumbing wrong
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