3rd Gen 4Rnr Rear Brake Proportion & Pressure
 

Hey All - after pulling the rear drums off, cleaning everything up and seeing how little my rear brake shoes have worn in 100k miles; I am wondering if there might be a way to mess with the line pressure to the rear brake circuit. Yes, I do have better rear brakes as a result of my adjustments (shoes allow one rotation of the drum before stopping when spun by hand without wheel/tire mounted); but the performance under braking isn't quite what I would like.

To that end I would like to know if anyone has investigated where working pressure is controlled in the rear brake circuit. On my old '87 Turbo-Rnr there was a frame-mounted rear proportioning valve actuated by a rod connected to the axel which effectively "added working pressure" to the brake cyls for the rear drums when the rear end of the truck squatted as a function of load. So while I was under the truck cleaning and adjusting stuff I looked around for that same proportioning system. Didn't see one. So I'm guessing it's elsewhere, or non-existent.

Here's what I would like to do. I would like to mount a tilton brake bias adjusting valve in the cabin to allow me to regulate the rear brake circuit pressure to allow better rear shoe engagement without needing to "drag" the brakes on the drum.

I've mounted Tilton valves on all the various race cars I've owned, I am simply looking for whether or not there is a fixed pressure limit valve to the rear circuit, or some other proportioning valve that I need to work around. Ideally I would like to feed the Tilton with full master-cyl working pressure and then manually adjust so as to have maximum rear brake engagement (without lockup) for my given load profile.

Why? Well even with the Tundra brakes up front, the amount of front-end dive under braking load is made greater by poor rear engagement. It gets a little ugly when I hang 500lbs of motorcycle & carrier weight to the back of the trcu plus 100lbs of gear inside. With an in-cabin adjustable brake bias controller I can best use the systems on the truck.

A search on the forum had effectively no relative posts on this topic that I could see.

I have a wilwood valve mounted to the frame to adjust my rear vs front brake pressure. I need to hone it down a little more, but I think that is what you mean (except you want yours in the cab).

Thanks! Yes that's what I mean.

So there is nothing currently inbetween the master cyl and the rear brake circuit that limits operating pressure when the truck is in stock form? Maybe my understanding is faulty but I seem to recall the operating pressures for front disks were much higher than those needed to operate rear drums - so I would expect a pressure limiter/regulator/proportioning system from the factory.

I am simply asking if anyone knows where it is.