So we converted a road tractor to a flatbed for hauling our counterweight for one of the cranes. We redid all the brakes/ drums as we were redoing the truck, but now that we've been driving around with it quite a bit, the guys are complaining that the brakes don't work that great on it. Its got jakes and we're usually just following the crane around, so we don't run too hard, but the brakes just don't seem to work quite like they should. A small light went on in my head- that there is probably a proportioning (bobtail?) valve somewhere in the system. We don't have a trailer anymore, so I'm guessing I can just remove the valve, or is there something I need to put in its place? And am I correct in assuming the proportioning valve will be after the treadle valve, and before it goes to the rear tandems? or will it be back by the rear tandems? Truck is a Ford l9000, set back front axle, 3406, 10 speed with a flatbed that was a former 5th wheel tractor.
The main service brake relay valve is probably a BPR-1 valve and looks just like a R-12 valve except it has two ports on top. One is for control from foot valve the other comes from the tractor protection valve. So when hooked to a trailer and red supply valve is in it puts air to the BPR-1 valve for full braking. The Bobtail Proportion is just that. Plug the port on tractor protection valve, the line going to the bobtail port just plumb it to a port in a air tank. That will trick it and give full braking.
Thank you
weird you would have to do anything. My L9000 dump truck is fine solo.
Your truck was likely dump from the get go- so its brake valve wouldn't be like the one I have. I should have thought of this while we were making it a flatbed, would have been a lot easier to swap stuff before we put the bed on.
It has the same valving and tractors can be driven solo. Color me skeptical that the very presence of a protection valve is the cause of your odd braking.
A quick way to test is to put some plugged off gladhands on the trailer lines (if you still have them on the truck) and push both knobs. My bet is you have the bobtail valve.
If it's a tractor built from 90 through 97 it probably has BP. As a ten wheel configuration loaded and with application gauge if you watched the gauge you would probably see your using 60 plus psi instead of 20 for control.
Well its got a valve under it, but its got a bundle of wires heading to it. I'm guessing this is some kind of primitive early ABS. There's no sensors on the rear tandems, I didn't look to see if there's any on the steers. It sure doesn't look like the images I found of the BPR-1 that you mentioned Truck Shop. I'm going to have to dig a little deeper. If I have time tomorrow, I'm blocking off the old red and blue lines for the trailer hook ups and load up weights and see how it does. Last picture shows valves that are feeding the control line.
In this last photo/bottom-the small valve to the right is either a TR-3 inversion valve or a RV-3 pressure reducing valve. The valve in the top two photos I believe is obsolete and don't remember its designation number. In the top photos the black/ green/ yellow are control, supply, delivery ports. Where are the two rubber hoses going? I'm supposing air cans-park brake ports or service brake ports? I'm going to suspect either the 5/8" green or the black are going to a quick release valve on the back drive axle. What year is this, because a lot of Fords crazy air systems are obsolete/ no parts. But that doesn't mean it can't be converted to a simple R12 and some quick releases for park brakes. Check to see if the tractor protection valve has four air lines or five.
So I've numbered some things up and gave some guesses. 1 and 2 run to the tandem axles, 1 to the front axle and 2 to the rear axle. They then split on top of each axle, running to the brake cans. #3 I think is supply from tank up toward the front. #4 I'm guessing is control, and it comes from the small set of valves that were in the last picture above- that you are calling the pressure reducing or inversion valve. #5 stuff runs to a extra air tank mounted on the other frame rail, and if I remember right, the other line at 5 goes back to the valves beside the pressure reducing one. I'm guessing to give a air supply to that back set of valves. I didn't get under it until late today. I spent some time trying to follow air from front to rear, and found the old trailer hook ups. I'll climb under tomorrow and try to make a diagram how everything is plumbed up. Truck is a 1995. Thank you for the help- I really appreciate it.
What the small set of valves look like to me is a early try at a SR-1 modulating valve which coordinates/modulates spring brakes for emergency stopping. I'm fairly sure that main valve is totally obsolete. Check those air lines going to the axles to see if those are service or park air hoses, I'm going to assume service.
The two rubber lines -I think they are service. The park cans were originally only on one axle, and we have to stop in some steep spots, so we added park cans on the other tandem. I think we t-lined off the original park cans, to release the second set of park cans. So that wouldn't be these lines.
I ran into the same deal but to make it worse the SPORTS CAR was a automatic. The guy had been driving it for 3 years and all at once he said he didnt have very good brakes. The trailer lines were plugged so i had him run it with both buttons pushed in then i replaced the valve i couldnt tell any diffrents. Like alot of " problems" i replaced the front shocks and never hear about the brakes agin.
Hey you, did you get that fingered out yet?
With the trailer lines plugged off, and pushing in the red button, I have great brakes on the tandems. Night and day difference. So there is definitely a bobtail function. There is some kind of primitive abs- there's sensors on the front axle, but not the tandems. I don't know if the rears originally had sensors also, but there's only sensors on the front axles now. Who knows if any of it works the way its supposed to. I'm thinking of just removing all the extra electrical and the goofy valves on the rear, and just going to a r-12 like you suggested. Thanks.