NEED HELP !!!

Sounds like the brake valve itself went bad. They are replaceable. Order a new one.

 

Mine is a 94, i had a similar issue and thought it was the brake valve like you mention. After I dig a little more I realize it was NOT the valve but the switch for the cruise control . So what I'm trying to tell you, dig a little further, it might be another issue close the the brake valve . @NorthernMechanic @wore out and others will chime in.

 

No cruise control in a 359 , but correct. Look for air in the vicinity. We will be kindred souls as we are also working on a 359. Ours has lots of air lines in that area. Start by cinching up the air line connections on the valves. Since the valve is new, maybe the air line has a crack due to messing with it and it now leaks. 30 year old rubber is not as flexible as new...

A bit of advice. We cruised ebay and were able to buy a owners maintenance manual that was printed the same year as our truck - 1978. Absolutely invaluable. No way could I have figured out how to fix stuff without it. The air supply schematic and wiring schematic are my close friends . Buy one. You won't regret it.

Some details are different between earlier 359's and later ones. Be aware.

John

 

Is it a tri axle with a pusher or a tandem. Anything could be cross plumed from the swap. If it's a triaxle odds are probably better that's it's something along those lines good luck

 

I have an 86 359 with factory cruise. It's an air operated cylinder under the cab

 

I'm trying to recall what would be in that portion of the air circuit.

I don't think it'd be a brake chamber, that would dump air either to atmosphere or out through the exhaust port on the service brake relay valve.

My 1980 W900 has a relay for the park brakes. Pretty sure most trucks are like that. IIRC the yellow knob only supplies a pilot signal to the relay valve and the air to the chambers comes direct from the tank. So even if the diaphragm in that valve was leaking, that air should not back feed from that relay to the park valve in the dash.

This truck being an '86, does it have 3 knobs or just 2?