Brake Proprtioning Valve

[Ian Gross]

Do we have a Valve that controls front to rear breaking force? It feels like most of my breaking is done with the fronts, which is what it sounds like most of our tracs are doing by warping rotors so fast. So if anybody knows if we have one and where it might be I want to fool around with it. I looked on the brake lines in the rear and I didnt really see anything.

 

[Bill Ellis]

It's simple physics Ian. On nearly all vehicles, the front brakes apply about 75% or so of the stopping force and no one can change that. When you apply braking force there is a downward pressure applied to the front which ulimately causes the front brakes to work harder than the rear brakes. No doubt here is some web site out there that explains this in detail; I could too but it requires some diagrams that I'm too lazy to draw and post here. There is no problem with warping rotors. What many think is a warped rotor is really a buildup of brake pad material on the rotors. You can do a search and find a link to an article that addresses that in great detail.

 

[Todd Z]

They are screwed on to the master cylinder, If you look right where the master brake lines come out you will see a block of aluminum, that is the proportioning valve...



The rears are applied first before the fronts, Just like a train... the rear car slows down first..



You can buy an adjustable proportioning valve but I think then you might cause the truck to skid or tear apart rear pads way too fast....



Also a FWD car the right rear and Left front are on the same line, it is not like a train...



Todd Z

 

[Ian Gross]

Bill I understand this phenomenon and im sort of trying to beat it. In my taurus there was a break valve that if there was more weight in the back appled more hyraulic power to the rear. Since it was located on the body and connected to the rear suspension, as what you described happened it would transfer more power to the larger front brakes. So what alot of us did was to trick this valve into thinking it was always open with a zip tie allowing the max breaking force to the rear. Some people took this a step further and removed the valve bodies all together and just pluged the holes which lead to the ability to skid like Todd is saying.



Reason Im thinking of this is to try to get a little more force out of the rear drums, I know I know convert them to discs, believe me thats in the plan, Im not going to waste my time changing the shoes.



Ill have to take a look at what Todd is talking about and see if i can get it to do what Im looking for, Im kinda doubting it though.

 

[Bill Ellis]

I don't understand your desire nor need to do this; but, consider what such an adjustment might do. When there is no load in the bed, too much brake pressure could cause rear wheel lockup which will then be overcome with the ABS. If your rear drums are not doing much work at all, they may need adjustment. Try that first before tampering with a system that was designed to work well.

 

[Todd Z]

Believe it or not if you do the math a drum brake applies more stopping power than a disk pad due to surface area, piston size and hydrilics...



The reason disks are used is cooling , parts, and maintainance....



Todd Z

 

[Ian Gross]

I guess part of the problem is that im intimidated by those things, which is sad considering I just replaced my front wheel bearing assembly.



I was compairing it to the Taurus system in that we could fool the valve open IF we had one. Doing this is sort of with in the Design of the system in the fact that your not applying tooo much force just more in certain circumstances, which could lead to engaging the ABS, but this is part of "testing", if it does then switch it back if not and it improves the performace of the rear brakes then great.

 

[Ian Gross]

Believe it or not if you do the math a drum brake applies more stopping power than a disk pad due to surface area, piston size and hydrilics...

I think this statement should say CAN apply more power. And maybe like Bill said mine just need to be adjusted.

 

[Bill Ellis]

Ian, remember that drum brakes self-adjust when brakes are applied while driving in reverse. I have the habit of coasting to a stop in reverse and then shift to drive. That does not adjust the rear brakes and after a while, they aren't doing much. So, if they are not too much out of adjustment. Backup down the street and pump the brakes sharply and the adjusters will take care of it.

 

[Gavin Allan]

Warped rotors are usually caused by improper torquing procedures for the lugnuts. Run them down in about three torque steps in a star pattern, ending with the last pass at the torque spec.

 

[Ian Gross]

Bill Ill have to give that a try and see what I get.



Gavin, Yeah you can still get them to warp esp if drive on the western part of the pa turnpike through the appalacians with a 3500lb boat and three other people and camping gear a few times.



Just a little FYI side note when I was at the scrap yard the other week the Trac weighed 4700lbs with 1/2 tank of gas and my 180 lbs in it.

 

[Todd Z]

you can also manually adjust the star wheels through the holes in the drums....



Jack up the back of the truck, click the star wheels a couple, and manually spin the tire, do this until the tire only spins 1 turn.



There is more to that but that is the basic way of how to do it...



Todd Z

 

[Yardsale]

When you get done looking for the star wheel adjusting hole in the drum, look for it on the backing plate (little rubber plug). ;-)