Air Brake Leak

[ejohna2000]

1986 PT 38 8V 92 The air brake front & rear tanks are at 120 PSI when I
shut the motor off. After about 30 min. both tanks lose the same amount
of air and get down to 60 PSI and will stay there for hours. If I leave
the parking brake in the off position the loss of air is much slower.
Have replaced the check valves in both brake tanks so they can not
bleed back into the supply tank. Can you give me any idea what would
change with the parking brake off or on. I have an ultrasonic leak
detector and have gone over the complete system many times and can find
no leaks. Elmer in Sebring,FL

[Hugh Turner]

Elmer
Have you checked the parking brake valve itself. The 60 psi point is
right around the point where spring brakes apply.Listen to the
backside of valve. Also check the treadle valve for your brake peddle.
More than likely it will be a very small leak. I have the print for
the air system if you need them. I have the opposite problem my brake
air holds great but my secondary air leaks down.
Hugh
PT40
Thomaston Ga


--- In WanderlodgeForum@yahoogroups.com, "ejohna2000" wrote:
>
> 1986 PT 38 8V 92 The air brake front & rear tanks are at 120 PSI when I
> shut the motor off. After about 30 min. both tanks lose the same amount
> of air and get down to 60 PSI and will stay there for hours. If I leave
> the parking brake in the off position the loss of air is much slower.
> Have replaced the check valves in both brake tanks so they can not
> bleed back into the supply tank. Can you give me any idea what would
> change with the parking brake off or on. I have an ultrasonic leak
> detector and have gone over the complete system many times and can find
> no leaks. Elmer in Sebring,FL
>