replace load proportioner w/ fitting

[87mjdriver]

I am thinking about taking out the load proportioner(sp) and replacing it with a t fitting for right now,

With full braking power going to the rear and riding on 35's I would think the chances or rear wheel lock up would be very minimal. any one agree???

90% of the time it is an empty truck bed.

[CWLONGSHOT]

That's not the way it works....

 

If your going to eliminate the rear proportioning valve, you only need one line for the brakes. That other line is a "safety" that allows front brakes if the rears fail (or is that versa visa :dunno: ) Anyhow, you need to plug the return line and only run one single line into the rear brake hose to the axle. IIRC its the line running out of the "nose" of the distribution block up front is the one to plug...

 

CW

[Pete M]

it's a safety line that allows full rear pressure to the rear should the fronts fail. :thumbsup:

 

You can either just splice in the T, splice in a union and cap the old emergency line at the front splitter, or (if you live in a rust-prone location) remove all the rear lines and run a new single from the front. (the brake line is prone to rusting out next to the gas tank)

 

[87mjdriver]

Ok guys thanks.

 

but what about the lock up ?

any body eliminated the proportioner?

[Pete M]

eliminating the prop valve has had mixed results. some have had lock-up problems, other have not. It's sorta hit or miss. If you do find you're having lock-up issues, you can always try an XJ front prop valve, or splice in an aftermarket adjustable one.

[dasbulliwagen]

I recently did this on the boss's MJ...it was having brake troubles and I was trying to eliminate things one by one. Someone replaced the rear lines before me and put a tee fitting in there at one point, so I unhooked the lines to the height sense valve, tied both of the rear lines into the tee fitting going to the rear brakes so if the front valve kicked in it too would go to the rear brakes. During hard braking the rear wheels would lock up... even moderate hard braking. It is a stock 4.0 4x4 on 235's. It ended up needing new front calipers for the braking problem. but lockup is an issue, just be careful.

[ncgamedog]

I just did this on my 91. I used a booster/master from a 96 XJ as well as the Prop valve from the same cherokee. I just reused the line running to the "T" before the LSPV in the rear and then a SS braided line down to the axle. I am running an XJ dana 44 rear with 10x2.5" drums and have NO problems with lock up running 245/75/16's. I enjoy some awesome clean braking now! hope this helps. I just picked up the parts from pull-a-part, I did replace the master w/ a new unit from auto zone.

[Eagle]

Rear lock-up is a potential problem when the load-sensing valve is removed, but IMHO swapping in a Cherokee proportioning valve is not the answer. I've been running the '88 MJ with no load-sensing valve ... I had no choice, it blew out in a panic stop. I had the rear wheels lock up once, when I was approaching a stop sign going down a fairly steep hill and there was sand on the pavement. Aside from that, it just feels like I have better brakes than any other XJ or MJ I've ever driven.

 

Why isn't the XJ proportioning valve the solution? I have a couple of reasons. The first is that the XJ proportioning valve is prone to gum up, resulting in NO rear brakes. That's the sutuation with my '8 XJ right now, but I have other things on it that have to get fixed first (like heat). The second is the way I think the XJ valve works.

 

If you open one up, there's a plunger, a cup washer (which most people refer to as an O-ring, but it isn't), and a spring. The spring tends to hold the cup washer toward the rear of the bore, such that NO fluid can pass to the rear brakes. Only when the pressure is high enough to compress the spring does the cup washer and plunger move out of the way to allow brake fluid into the rear brake circuit.

 

At least, that seems to be the only way it can operate, based on the way it's constructed. What does that mean in operation? If I am correct, it means that under most normal conditions you are stopping only with the front brakes. You get rear brakes only under heavy/hard braking. BUT ... that's exactly when the vehicle weight is shifted onto the front wheels and the rear brakes are most likely to lock up prematurely, so in reality that exactly when you DON'T want full braking to the rear.

 

I'm happy with the MJ metering block and no proportioning valve. I know I can't drive like a maniac when the pavement is slippery ... so I don't.

 

I don't think the tire size makes much difference. With larger tires you have a bigger contact patch, but you also have the same weight on the contact patch, so the pressure of the tire on the pavement is lower in psi. In fact, if it works like driving in snow, you'd probably do better with smaller/narrower tires.