Air leak?

Sounds like your valve assembly in the dash is that where it’s leaking in the dash???

 

Sounds like you have a damaged air cylinder the automatic transmission your driving or theres a hole in the air line to your splitter

 

This is stuff they teach or are supposed to teach in cdl school.

Do you not know how to diagnose an air leak? Do you not know how to do an in cab air brake test? What are the rules/guidelines for air pressure? How many lpsi can a system in a combination vehicle drop in 60 seconds?

 

you hear air leaking.

the air gauge drops.

nope, no air leak.

 

Well, at least the OP realizes there's an issue and is asking. Gotta give him/her credit for that.

But, yeah they should have taught such things in school.

OP, did you even attempt to locate the issue? Try releasing just the tractor brakes, make sure the trailer brakes are set. Does the air leak? If it does, the problem lies in the truck. If not, set the tractor brakes and release the trailer. If it leaks, then it's likely the trailer.

Or try shutting the truck off, block the wheels so it don't roll away, and release the brakes. Then get out and listen for air hissing outside.

 

You cant evdn figure out where the air leak is, yet want us to tell you how long it'll take to fix it?

Okay. Between 5min and 20 hours.