Hello,

Re: 1985 F-250HD, 4x4, 460ci, Sterling 10.25 rear,

Was inspecting brake lines and found the oddest arrangement at the rear.

The break line comes from the front of the vehicle than attaches to a block of sometype that is mechanically coupled via an odd half-moon arm arrangement that is than bolted directly to the differential housing. From that block another line comes out that goes to a smaller block. In this block the lines for the right rear wheel break and the left rear wheel come out eh sides and go to the wheels. but from the top of this block comes another rubber hose that is capped off and goes above the spare tire.

The only thing I can think of for the mechanical attachment is if the axil got jumping around too much it might apply some break pressure to the rear wheels and I don't have a clue what the capped off line is

Can anyone explain?

Thanks

nonrev

 

I can help on this part... It's a combination brake line tee, and axle vent. Rear brake line in, and then out through left and right sides to respective wheels.

Bottom of block has access to axle/diff air space, and the top has a rubber hose that goes up to a drier place, where it should not get submerged.

Can't help on your other block's description.
Some cars/trucks have a suspension height-operated valve in the rear line to adjust rear wheel line pressure versus cargo loading. But the arm on those has to go to something that moves with loading, versus where the valve is mounted.
Did not see that bit in your description.

 

Thanks for the info

 

That was a control valve that regulated the amount of rear breaking the rear wheels would do in relation to the amount of load in/on the truck, put weight in the bed, when suspension squats the link moved the arm opening the valve increasing rear brake pressure, remove the load and the pressure was lowered, keeping the rears from locking up under light load, heavy braking. I had a lot of tow trucks in those years and that valve was the cause of a lot of white hair when they quit working, it seemed they always went bad in the low pressure setting limiting rear brakes, not a good thing with a big car or truck on the hook. We always took them off and replumbed the lines. The line that goes up by your spare is the vent line and is not capped, what looks like a cap was a vent fitting to keep crud out.

 

Hello,

That's it, I went out and looked at the design. The arms are arranged such that any load in the bed (actually load on the springs and suspension bringing the axil closer to the bottom of the bed) would compress the arms and apply some small amount of rotational movement to the arm connection at the side of the proportional valve. Interesting

 

Hey Jetjocky99.

I plan on pulling a trailer for a few years while my wife and I travel around when I retire. I sure don't like that event you mention about them going bad and limiting rear brakes.

I am having a HydroBoost installed so that should help braking but would you advise taking this thing right off? What are the symptoms when this proportional valve on the rear goes bad?

Thanks

Rgds

nonrev

 

I would remove it before I did any towing I had them on both Fords and Chevys and I don't remember what fittings I used to bypass them, but it was simple to do. If the valves go bad you will have either reduced rear brake performance, the most common in my experience, or you will have full power rear braking and the rear wheels will or at least can lock up much easier with no load. Locking the wheels up under low load was much less of a problem than almost no rear braking under heavy load. They also tended to be a source of fluid leaks as well. They where a good (?) idea that was poorly integrated.