When I let off brake peddle, trailer brakes still have pressure applied

Sounds like you've got a sticky valve in the truck somewhere. Try and use the trolley valve only if you have one and see if it still does it.

 

WD40 the peddle works best

 

Check your air lines between the truck and trailer for a crimp. Any slight crimp or bend in the lines can cause the brakes to drag. Maybe you stepped on one of them while connecting the air lines to the trailer.

 

Go under truck to look at air release rubber cover on bottom of foot valve and service brake valve, dirt dobbers, ants can build up nests and block air from ex.

 

You have a trailer air gauge that's reading....

Wait! You have a trailer brake pressure gauge??????

And it's reading 120-130 psi?
And you didn't blow a brake chamber yet?

I think this operator doesn't know what they're looking at while looking at the dash.

If your getting 120 psi brake pressure, your giving way too much pressure.
Should only require (estimate here) 40-80 psi.

 

Seems to me problem is more complicated
first of all check brake lights. Brake light relay is usually actuated by 0.3-0.4 BAR switch in foot brake valve line. It they are off - be sure foot valve is OK.

Now u have to chekc what ia bad - TCV ore valves on your trailer.

TCV _ trailer control valve. It is supplied from tank #3 (trailer and park brake tank), controlled by lines from foot brake and trailer hand brake lever (via choose max pressure valve) and as output blue (control) and red (supply) lines are used.

To check it u need glad hand with 200 PSI gauge.

Fit it on control line first and check for pressure, If u can see it - loosen TCV control lines becouse tube may be collapced it truck frame and some control ait may stay there. After that do all TCV rebulding procedures ore change TCV.

Ok. If u can see no trailer blue glad hand problems - it is not all. Sometimes if TCV supply line is collapced ore tank #3 valve is bad and pressure in tank is low - in red glad hand pressure may go too low and PREV valve on trailer applies brakes, becouse low pressure in glad hand is signal to apply brakes too!

 

What if he doesn't have three tanks, and why would you need a 200psi gauge when the entire system gets to 150psi max.

Why do people keep saying these air pressures are in the mid hundreds?

 

Mechanical gauges are most accurate in the middle of their range. Plus you want a bit of a safety factor.

 

Context please.