I'm working on changing my 8.8 rear axle from drum brakes to disk brakes. I have collected the parts off of an explorer and have read through the how-to's. My main question is whether or not a proportioning valve is necessary??? My truck originally came with a 7.5 axle with 9 inch brakes. I converted it to a 31 spline 8.8 with 10 inch brakes. Now it seems to me an after market adjustable proportioning valve would be necessary in order to get proper brake pressure distribution. On TheRangerStations tech instructions, there are step to adjust the master cylinder pushrod, but I don't believe that would help the pressure distribution.

 

I didn't with mine and my truck stops way better with the disc in the rear. I dont think its necessary.

 

I asked the same question and I was told the the Explorer proportioning valve is not needed.

 

Well that is very interesting then. I know with my current brake setup, my front brakes lock well before the rear brakes. Does anyone know of a way to find out the brake pressure being applied? A way to look up the information, maybe from Ford? I know Bob has mentioned some brake pressure before in his thread.

Keep the comments coming!

 

True for 2001+ Rangers which have Electronic Brake Force Distribution (electronically controlled proportioning provided by the 4WABS system).

By contrast, Rangers from 2000-back used a mechanical proportioning valve and may need a change in the proportioning curve to help prevent rear wheel lock up when rear discs are fitted.

 

Thanks for the info Bob. As for the proper way to proportion the rear brakes, I was looking to run a Summit Adjustable Proportional Valve, and tie it into the brake line system after the stock proportioning valve, before the line splits to both rear brakes. Any input?

 

your front brakes should lock up b4 your rears

 

There is less weight in the back of a truck because of the bed so the rears should lock up before the front that's why trucks used to only have rear abs.

 

rears should lock up first. haven't you seen chuck norris lock up his rear brakes on walker texas ranger? jeeze lol

 

my fronts always lock up first no matter what i am driving

 

When you stop the weight of the vehicle transfers to the front and the rear will lock up before the front. That is why more braking force is applied to the front. In a car usually the front will lock before the rear but in a truck the rear will always lock before the front because of this weight transfer and the lack of weight in the rear. Your brakes must not work then.

 

1st, remove the stock valve and replace with the new one, don't run double proportioning valves,

if the truck is set right the front will lock first, it is designed so that you understeer and any collisions are taken in the crumple zones (locked rears would make you spin around) even without the proper proportioning valves and such the master cylinder still pushes less force to the rear along with the rear having less brake surface area so that will also lower the effectivness of the rears so that they do not lock as easy as the front, if everything was equal then yes the rear would lock first but nothing in the equation is, say with my truck, my front is 2 piston, 11.75" (I think, whatever the new rangers are), so if I went 10" single piston in the rear the front would have hella mechanical advantage over the rear even if the MC was pushing equal fluid pressure, also look at the pad surface area, my fronts are a good 6 inches long, the rear is 3",

 

^^^ thank you. im glad i was right for once i knew the front brakes were suppose to lock up first.

 

I said earlier that more braking is done up front. The reason the rear brakes usually lock up on truck is because of the lack of weight. It is so simple to understand. That is why trucks first had rear abs. They didn't only put it in the rear because they had a problem with the front locking up.

^^Right there.

 

Could you elaborate some more please. What is the issue with running two proportioning valves? The main proportioning valve I know of on my truck is on the inside of the drivers side frame rail up near the motor, but off hand I can't remember how the brake lines are split from there (To the front and rear, just rear?) Maybe some of the SAS guys know more about setting up an adjustable proportioning valve?

 

Rob a general rule of thumb is drum brakes take around 10psi to push the pads out and calipers take around 2psi.

You will need the proportioning valve to control that pressure. Also there maybe another valve called a residual (sp?) valve that holds pressure in the line, but I cant remember if your truck would have one or not.

 

Well that a good real to start with then. It would seem that for the people who have swapped to disc and not change the valve, would be getting rear lock up much quicker than the front then.

On your truck, I know you had an adjustable valve, did u remove the stock one?

 

Well on 2000 and newer the stock valve is located in the abs module, so yes i removed it.

I would try it without first. If it needs it then add one from summit for 40 bucks.

 

The summit 40 dollar valves are the main ones i have looked at with a single in - single out, my main question would then be where to add it to the system? I would think after the stock proportioning valve before the rear brakes, that way the rear brake pressure could be reduced. Not sure if that is the correct way though.

 

yup i think you are right on track. that is where i would put it.

 

The 2000-back Ranger proportioning valve controls the front-to-rear pressure bias by limiting the rear brake line pressure. Ideally, the harder you push the brake pedal, the greater the braking power bias should be toward the front. This is important because the harder the vehicle is braked, the more weight is transferred to the front wheels/tires.

The ideal relationship between the master cylinder pressure and the rear brake pressure is described graphically by a nonlinear curve. In the real world, the ideal curve can be approximated by two straight lines with different slopes that meet at the "kneepoint".

Generally speaking, below a proportioning valve's kneepoint, the front and rear pressure is equal; above it, the rear pressure is a fixed percentage of the front pressure.

A factory proportioning valve is set up to match the stock brakes and almost always has a fixed kneepoint. The adjustable proportioning valve allows the kneepoint to be moved to better approximate the ideal curve after modifications.

I agree that the correct way to install the adjustable valve is to replace the original valve.

 

Residual valves are not about lockup. They determine how much residual pressure remains in the lines after the brakes are released.

The higher pressure residual valve for drums prevents the springs from fully withdrawing the shoes which would lead to long pedal travel on the next stop. The lower pressure residual valve typically used with discs helps reduce brake drag because disc calipers do not have return springs.

 

Thanks for the info Bob. I will roll under my truck this evening and take a better look at the stock valve as far replacing it with an adjustable. I'm just not sure whether or not a simple 1 in - 1 out valve will work.

 

After installing the proportioning valve take a test run.
Hit the brakes hard and see if the rear lock up; if they do reduce the rear pressure until they don't lock up any more.

Some proportioning valves actually work as a brake safety valve too, so leaving it in line might be a good idea; not sure.

 

So I finally got a chance to roll under my truck and take a look at how the brake system is set up. From the master cylinder there are two lines that lead off. One goes to the front of the truck where it is T-ed off to both from brakes. The second line leads down between the frame rail to a proportioning valve that then proceeds to the rear of the truck..

It seems a simple single in single out adjustable proportioning valve will work in place of the proportioning valve. My question is, the stock proportioning valve has a 4 prong wiring plug on the side of it. What is this for? My truck does not have ABS so i'm not sure when the electronics would be for.