Air Pressure Drops 20psi With Every Brake Application 05 Diplomat...

[1doodadd]

The air loss has Nothing to do with brakes being out of Adjustment. It as simple as your brake chamber diaphragm is damaged and no longer sealing in the chamber and allowing air to escape the sealed chamber during application.

You will need someone to apply the brakes while you walk around the coach and listen for the air leak to find the correct brake chamber diaphragm leaking

[CountryB]

I think it can to some extent. Not air loss - but excessive pressure drop.

If you had a broken slack adjuster (or clevis), but not a leaking diaphragm, when you step on the brake pedal, air will fill the brake chamber and push the diaphragm to the "maximum extent" (air will completely fill the brake chamber). That will be a lot more air then is normally needed to push the chamber diagram the inch or two it would normally travel if everything was working and adjusted properly.

Then when you release the pedal, all the air is going to dump out the relief valve. Which could explain the large initial pressure drop and excessive air dump you hear when you let of the pedal.

In this scenario if you held your foot down, the pressure would stabilize and hold at some psi.

I don't know if the pressure would drop from 120 to below 65 (for low pressure warning buzzer to come on) with just one brake pedal application, but it would certainly drop a lot.

[twinboat]

Out of adjustment brakes will certainly cause excessive air pressure drop.

The brake chambers are 30 sq inches with a 5 inch stroke. Normal movement is 1 inch.

Get a buddy to step on the brakes, while you watch the rods, coming out of the chambers, move. Do this with the parking brake OFF ( button in ).

If the rod moves more the 1" the brakes are out of adjustment.

If the rods look like they are already out and don't move at all, the brakes shoes are worn and the S cams flipped. Not likely but it happens.

[Unplanned Tourist]

Originally Posted by twinboat

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If the rods look like they are already out and don't move at all, the brakes shoes are worn and the S cams flipped. Not likely but it happens.

Cammed over brakes, happens. Have the brakes been spiked lately? If they were worn beyond min. pad thickness and he had to make a sudden hard stop, that could do it.
Happy Glamping.

[MonacoMan84]

A lot of great info posted here. I will start by having them inspected an adjusted, I will post pics and progress....

[DiplomatDon]

MonacoMan, 43 years and over 3 million miles of driving truck tells me you have a leaking diaphragm. Do as suggested, build air pressure, release parking brake, have helper step on brake while listening at all four corners. Willing to bet one corner has serious leak. If one or more brakes were just out of adjustment, problem would have come about very gradually. I wouldn't ask the RV tech who thought out of adjustment was the problem any more brake related issues. Good lick and let us know. Don

[guardrail53]

Originally Posted by 1doodadd

The air loss has Nothing to do with brakes being out of Adjustment. It as simple as your brake chamber diaphragm is damaged and no longer sealing in the chamber and allowing air to escape the sealed chamber during application.

You will need someone to apply the brakes while you walk around the coach and listen for the air leak to find the correct brake chamber diaphragm leaking

X-2 Brake Chamber (Doughnut) bad!

Originally Posted by DiplomatDon

MonacoMan, 43 years and over 3 million miles of driving truck tells me you have a leaking diaphragm. Do as suggested, build air pressure, release parking brake, have helper step on brake while listening at all four corners. Willing to bet one corner has serious leak. If one or more brakes were just out of adjustment, problem would have come about very gradually. I wouldn't ask the RV tech who thought out of adjustment was the problem any more brake related issues. Good lick and let us know. Don

Same X-2 Listen to the Truck drivers!

Rail!

PS, Take your MH to a truck shop, or have a Mobile Truck Mech. come to you, and fix it right! And you will save some money too!

[moisheh]

In today's world OTR truck mechanics are not supposed to adjust the slacks . If your brakes are out of adjustment there is an underlying cause that must be repaired. However what the OP describes sounds like a brake chamber with a hole in the diaphragm.

[CountryB]

If the brake chamber diaphragm has a leak, it will continue to leak while the pedal is held down (brakes applied). So its easy to locate.

If the air pressure drops (a lot) but then holds steady (this is without the engine running so no air is being add by compressor), then it is possible that there is a broken brake chamber pushrod, clevis, or slack adjuster which is allowing the brake chamber to fill with air more than normal (as I described in my post above).

I'm not clear from OP's post if his air pressure drops and stops, or if it continues to drop.

[MonacoMan84]

Originally Posted by CountryB

If the brake chamber diaphragm has a leak, it will continue to leak while the pedal is held down (brakes applied). So its easy to locate.

If the air pressure drops (a lot) but then holds steady (this is without the engine running so no air is being add by compressor), then it is possible that there is a broken brake chamber pushrod, clevis, or slack adjuster which is allowing the brake chamber to fill with air more than normal (as I described in my post above).

I'm not clear from OP's post if his air pressure drops and stops, or if it continues to drop.

To clarify the pressure holds endlessly while the pedal is depressed. It only drops dramatically after releasing the pedal.....

[walt2137]

Im with Diplomat Don, when i had a air loss driving down the road i could see the compressor cycling about evert 2 or 3 min , I parked the coach blocked the wheel releases the park brake and started the coach and in my case it was the inversion valve leaking and replaced.

[MonacoMan84]

Originally Posted by walt2137

Im with Diplomat Don, when i had a air loss driving down the road i could see the compressor cycling about evert 2 or 3 min , I parked the coach blocked the wheel releases the park brake and started the coach and in my case it was the inversion valve leaking and replaced.

In my case I don't have any air loss, even while the pedal is depressed. Only when it's released.....

[twinboat]

If your gauges drop when taking your foot off the brake it may be your inversion valve.

Are you doing this with the parking brake on ?

The inversion valve sends air to the spring brake chambers to release them, as you apply air to the service brakes. That is so your not compounding the brakes.

[Unplanned Tourist]

Originally Posted by twinboat

If your gauges drop when taking your foot off the brake it may be your inversion valve.

Are you doing this with the parking brake on ?

The inversion valve sends air to the spring brake chambers to release them, as you apply air to the service brakes. That is so your not compounding the brakes.

Ahh, I was trying to figure out what you were calling the "Inversion Valve"!
We call it the "anti-compounding valve" here.
Happy Glamping.