1 ton rear axle propotioning valve.

[Gulfstream Greg]

I was told by the previous owner that my proportioning valve had been upgraded to the larger 1 ton version. So that brings up a question is there two diferent ones. pre 87 etc..

Here is a pic of my valve. 86 Sunrader

[nolan]

Good question Greg, don't know if the later 1 ton's used a different prop valve or not, but from your picture it looks the same as the 81 4x4 I have, if anything I imagine it would be internal valve size that would be different if any difference at all. Looks as though yours is set where it should be from the location of the boot and rod, fully compressed for max rear brake pressure.

[Gulfstream Greg]

Nolan

Do you know how that rod works? I have not a clue how that whole contraption works.

Greg

[nolan]

Greg, The prop valve on the frame rail has a piston that slides up and down and is connected to the rod that goes down to the rear diff. Just for explanation, under normal load and ride height the piston is centered in the valve, as you increase weight the rear drops the rod pushes the piston up and that in turn raises rear brake fluid pressure when stepping on brake pedal. Under hard braking the nose of the truck drops the rear lifts, the rod pulls the piston out and that decreases rear brake pressure to keep from having rear wheel lockup, common with an unloaded pickup, not so much a problem on a weighted down motorhome.

Adjustment is normally preset at factory and to readjust is pretty much trial and error unless you have the right equipment and figures, as it requires a brake pressure gauge to check the actual line pressure. Usually on the heavy motorhome with extra rubber on the rear, rear lockup is not common so full brake pressure works fine, if you do experience some lockup under hard braking then it could be adjusted by shortening the rod adjuster on the diff or adjusting the valve upward on the frame rail if it has the slotted bracket like some I have seen.

[ps4u]

Is this something I can add to an '83 to improve breaking. My RV locks up easily when breaking (and scares the oooo out of me). If so, what would you expect the cost to me and where would I find it? Thanks.

[Gulfstream Greg]

Is this something I can add to an '83 to improve breaking.  My RV locks up easily when breaking (and scares the oooo out of me).   If so, what would you expect the cost to me and where would I find it?  Thanks.

I can not see why not. Check with Toyota on the 1 ton Prop valve. Have no idea how much. The only problems I could see is mounting holes and maybe the size of the brake lines. Which wheels are locking up? The way the valve works is when you break the front of the truck dives down and the rear raises. The rod on the Prop valve moves with the rear axle, as the axle becomes farther away from the truck the valve is supposed to apply more braking power to the front and less to the back. You need to get a chiltons or toyota service manual to find out where its supposed to be adjusted to. From what I have learned mine was upgraded to the 1 ton valve but only because my rear axle has larger brake drums and cylinders for the 15 inch wheels.

Hope that helps.

Greg

[nolan]

Your 83 should already have a factory prop valve installed, either mounted on the rear frame rail or possibly just under the master cylinder/ brake booster under the hood. Normally with the weight of the motorhome, duals on the rear, rear wheel lockup is not common even when the valve is adjusted to full pressure, and the brake system is operating correctly.