Air brake issue.. any ideas are welcome

[#1FordFan]

Did it pass the 4 point air brake safety check during the pre-trip inspection?

The bus obviously has a intermittent problem if such a large leak was present the moment he started the bus he would have NEVER had enough air pressure to release the park brake.

It is very possible to pass the air brake test and then a mile down the road a valve stick open and cause a big pressure drop even with a perfectly good compressor.

 

[Rivetboy]

WOW. “Emergency failure mode” ??!
I never heard that term before.

You know it sounds like his brakes work just fine. (Sounds like safety features built into modern air brake work as well) His problem is intermittent air supply.
It seems he has a quite large air leak one moment . And no leak (or one much smaller) the next.

That sounds like a prime candidate for sticking dryer valve. At least that is where I start looking.

Commas are your freind, his brakes went in to emergency, failure mode (air pressure)

 

[Rivetboy]

Commas are your freind, his brakes went in to emergency, failure mode (air pressure)

Loss of air pressure = emergency application

 

[meyermobile]

I think that's what it was too. The pressure remained good for the remainder of the trip. I'm going to service the drier, and the governor and of course check for any other leaks.

 

[Sehnsucht-SKO]

The bus obviously has a intermittent problem if such a large leak was present the moment he started the bus he would have NEVER had enough air pressure to release the park brake.

It is very possible to pass the air brake test and then a mile down the road a valve stick open and cause a big pressure drop even with a perfectly good compressor.

Which is why I asked the question. I am aware however that too many people drive these like it's their car where they just hop in and go without taking the time to properly pre-trip the vehicle but I wanted to give the OP the benefit of the doubt. It's not an intermittent problem if it occurs more than once but is ignored - that's a recurring symptom of a problem that's probably going to leave you stranded sooner or later because you chose to ignore it.