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air pressure droping to much when you step on the pedal


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The most obvious cause for this would be a leak in the system. Can you hear any leaks with the engine off? If not you might need to find someone to work the brake pedal while you check around/under the truck. If it is a leak, it should be easy to find with such a large drop in pressure.

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Jim

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Yeah what green dash said, it's most likely to be a leak. Have someone work the pedal for you and snoop around, could be a blown diaphragm in an air can. Either way the leak should be on the service side of your air system in case you need to start tracing the airlines.

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The problems we face today exist because the people who work for a living are outnumbered by the people who vote for a living.

The government can only "give" someone what they first take from another.

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thanks for the quick response. checked for leaks this morning. found one small one, but I don't think it is severe enough to cause such a drop in pressure. purged the tanks did find condensation with a little oil. but still doing the same thing. the air does not continue to drop while you are pressing the pedal. it drops as air moves from the tanks to the chambers. then holds steady. I did have someone work the pedal while I listened for air leaks. no chambers are leaking or valves that I can hear.

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The rubber diaphram that the air pushes to actuate the brakes. Here is a picture to show you the parts.

4-1.jpg

I would guess that the truck has relay valves for the rear. Maybe an issue there? There has to be something that is dumping large volumes of air. How many air tanks on the truck?

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IMG-20180116-202556-655.jpg

Larry

1959 B61 Liv'n Large......................

Charter member of the "MACK PACK"

 

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HeavyGunner, could you elaborate on the what, when, and where. of a bad diaphragm in a can. thank you

What freight train posted above

The problems we face today exist because the people who work for a living are outnumbered by the people who vote for a living.

The government can only "give" someone what they first take from another.

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