This is a question for a friend.
He bought this truck new (90 pete 379 dump truck) and the other day he noticed that when he dumps the air for the rear bags ( Pete airtrack ) that it's not exhausting at the leveler valve like it used to.

It's dumping the air at a relay valve behind the cab. He has replaced the dash toggle valve the Relay valve and the leveler valve and it's still doing the same thing. He said the leveler valve works fine when going down the road, exhausts properly.
He said he hooked up the new relay valve properly, replacing one line at a time..3 lines total.

He was working it one day and it worked properly...the air would exhaust at the leveler valve. Then he dumped the air again later in the day and he could tell ( hear ) it was exhausting closer to the cab at the relay valve.

He's baffeled ??