I have a 1994 Peterbilt 379 It was a road tractor at the time of purchase. We took sleeper off and lengthened truck for log truck.It has had terrible brakes ever since. You have to stand on the pedal and then they will eventually work. Seems like I've heard someone in the past with similar issues on using a road tractor when it is not hooked to any kind of trailer. They said something about hooking glad hands to each other when truck isn't attached to trailer and it would give you better brakes. Anyone ever had any experience with this or does this sound crazy. Thanks
many fifth wheel trucks had "bobtail proportioning" valve. without trailer, only small amount of air to drive axle brakes, more to steer axle. you can put a dummy glad hand on , then push the red "trailer charge " valve in and have better brakes. proper thing to do is remove the bobtail valve (BPR-1) from system . http://www.manualslib.com/manual/392604/Bendix-Bp-R1-Bobtail-Prop-Relay-Valve.html?page=3#manual I would replace with an R-12 or R-14 relay http://www.manualslib.com/manual/392673/Bendix-R-12-R-14-Relay-Valves.html 525isx
525isx is right. Ran into that a few times people converted to flatbed and left the same valve. Limits air because it thinks your bob tailing all the time.
I had a interesting experience bombing over the billings scale bobtail with that problem. Run a supply line from the primary tank to the valve and viola done 100% brakes all the time. I cant remember what line but its 1/4"
It is a little confusing here because being a log truck you would think the red trailer supply knob would be pushed in when loaded, unless it is some kind of straight truck hauling logs. Unless the brake problem is only when empty? Nevertheless it does not need a bobtail proportioning valve because the dolly will be loaded giving the drives weight even when the truck is deadhead.
I'm thinkin' it is used as a straight truck -- he is in North Carolina -- they probably do things a little different than our stinger steered west coast trailers !!