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Brake Test Fail

April 18, 2019, 04:14:35 pm

While fixing something else, needed to raise the rear a bit to make it easier to work on.  While doing this decided to do a brake test.  Built up pressure until cut out occurred at 120 psi.  Shut off engine and applied service brakes.  Pressure dropped about 15 lbs over a 2 minute period.  Both needles dropped at the same rate.  I have taken it to a shop to have it looked at.  The owner had gone to lunch and a doctor's appointment, but his employee on a creeper rolled around under the coach and didn't find anything, just listening.  Built up pressure,  shut off engine,  and while I applied brake, he went under again and didn't find anything.  Pressure dropped about 30 lbs over a 10 min period with me applying the brake.  Other wise everything seems to be normal while driving.  Any ideas about what the problem is?

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Re: Brake Test Fail

Reply #1 – April 18, 2019, 04:50:42 pm

Shouldn't need soap to find a 15 PSI leak in 2 minutes (assuming steady peddle pressure, not pumping them).

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Re: Brake Test Fail

Reply #2 – April 18, 2019, 05:35:18 pm

Dont forget the brake button .. not sure if its able to leak when depressed but I think its worth checking also

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Re: Brake Test Fail

Reply #3 – April 18, 2019, 05:54:25 pm

There are pneumatic relay valves that supply the brake diaphragms. They can leak and are hard to hear. I have replaced quite a few of them on trucks and cranes. Soap test finds them. Follow the air hoses from the brake can back to where the valve is.

VALVE PLUS

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Re: Brake Test Fail

Reply #4 – April 18, 2019, 06:29:49 pm

Thanks everyone, yes steady pressure on the pedal, didn't think about the pneumatic relay valves, I don't think the brake button is leaking.  Coach doesn't hold air pressure like it used too when static.  Rained last night, managed to get out of the storage lot without getting stuck in the mud.  Just didn't feel like going under the coach and crawling around in the mud.  Planned on leaving Tuesday for 3 weeks, running out of time to get ready. The shop owner is back, said he would call when he finds something. 

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Re: Brake Test Fail

Reply #5 – April 20, 2019, 01:06:33 pm

The owner of the shop said he did the brake test and it passed.  Brought the coach home yesterday and tested it and it passed, maybe it just needed driving a little bit.  Magic!

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