Brake distribution valve thingy

[Matt Vee]

Does anyone know how the brake distribution valve thingy actually works?
When I was welding up the back end of my chassis a couple of years ago I had to cut this off at the bracket as the bolts had become one with the bracket. After finishing rebuilding the chassis rails I just welded the bracket back on where it looked like it was meant to be.
However, whilst sorting my hand brake out (again) the other day I noticed the pistons in the caliper on both sides were basically seized up and the outer pads were near enough fkd whilst the inner pads were almost new. Seeing as I changed these last at the same time as the chassis rebuild I deduced that I had fucked up the positioning of this valve and the rear brakes were hardly moving under braking and hence had seized up or something like that, dunno.
Anyway my question is, how does this thing operate? not as in what's inside it, I understand how the valve works itself but rather the activation of said valve. With the truck at ride height there is bog all tension on the spring and it is just flapping about in the wind. Is this the correct situation? Should there be more tension on the spring with the suspension in neutral position.
I am assuming possibly incorrectly that as there is more load on the rear, like when towing etc the spring comes under tension and pulls the shuttle valve across thus allowing more fluid to go to the back brakes than under normal non towing driving?
Am I just making this up in my head?
What is it actually for?
How should it be set up?
I have both a haynes manual and a max elery book about the truck but cannot find anything about setting it up in them, just says to replace it lol.

Thanks dudes and dudettes

 

[SteveJB]

Think you might be on about the Load Sensing Valve if it has brake lines in and out of it I have removed mine altogether and replaced with a t piece had no problems in over four years and think if you are only wearing brake pads on one side then sounds like your problem is in the callipers themselves and am assuming your handbrake is the same as drum in disc and not been converted to a hydraulic system

 

[AdventureWagon]

Yeah what you described is how it works, more load on the rear results in more braking at rear. I think there's almost no braking on the rear at minimal load.

Not sure how is set up but can get some pics of mine if you want to compare.

 

[SteveJB]

Just had a look see at my haynes and ellery books in haynes chapter 9 11 gives you a measurement of A = 90 mm between centre of fixing pins and in ellery page 271 gives you a whole load of words to read and follow good luck for removal or adjustment

 

[Shayne]

I never messed with my brake valve but i was interested to note while investigating stupidly high lift kits (to gain understanding) that a lowering bracket for the valve is often included . What logged was "nothing more - just lower it

 

[Matt Vee]

Thanks guys
That is very odd, in my haynes book I cannot find anything relating to setting it up. It just says "if a new or replacement load sensing valve installed, have the valve adjusted by an authorised dealer or a brake specialist"
In my Ellery book page 271 is about a limited slip diff, how odd.

In the haynes book however there appears to be an adjuster on the pan hard rod, mine just has the spring hooked over the little bracket that clearly is meant to have an adjuster.

Ok thanks people I shall continue to attempt to resolve the mystery and if that doesn't work, T-Piece it is!

 

[Chris]

Effectively it's a needle. Like a small pointy thing that slides in and out of a corresponding hole. It restricts the fluid flow meachanically as the arm goes up and down. Unless of course it gets full of crud and doesn't move anymore. They also leak after a while. Probably due to being closed and the brake pressure busting the seal.

 

[Matt Vee]

ok cool thanks, so it's most likely in a "normally closed" position then?

 

[Chris]

Great question Matt. Can't really remember. I'd have to get under one and stare at it for a while. As the back end lifts, it should reduce the fluid supply to prevent lock up.

 

[Matt Vee]

That's how I figured it worked. This is what I think caused my calipers to seize up. Hardly moving, shit building up in the slider pins maybe, when they move they pull it over a bit and a bit more and a bit more etc till the outside pad is near enough dead and the inner pad is hardly worn. I have new pads coming today so I want to try and work out wtf is going on before I put them in eh.

 

[Chris]

Sounds about right Matt

 

[Matt Vee]

Ok finally got round to finding the info in the ellery book I have, it's on page 319 in mine. Seems the spring needs to be under at least some tension when at ride height, mines as slack as mince. The measurement is taken from the centre of the lever pivot to the head of the adjuster where the spring clips in:

SWB: 220mm
LWB: 222mm

More tension on the spring= less brake pressure on the rear brakes
Less tension= more brake pressure on the rear brakes

So seems like it is a valve in normally open, which makes sense because then if the spring snapped the rear brakes would still have pressure.

 

[Matt Vee]

That's how I understand the theory, find out tomorrow if I have won the contest for least understood concept of 2020