rear axle thing on MJ. maybe xjs too?

i have no idea what this thing is, but its located above the rear axle. it has steel lines coming out of it with i dont know what in it, and it has a pivoting arm that comes down and attatches to the axle housing. the only thing i could think it to be is like a hydrolic rear axle stabilizer or something. who knows what it really is?

stupidfast said:

i have no idea what this thing is, but its located above the rear axle. it has steel lines coming out of it with i dont know what in it, and it has a pivoting arm that comes down and attatches to the axle housing. the only thing i could think it to be is like a hydrolic rear axle stabilizer or something. who knows what it really is?

Click to expand...

It's a break pressure control, when you add weight the springs go down and the break pressure goes up.

As Laner1 said, it's an adjustable proportioning valve that senses ride height changes and adjusts the rear pressure accordingly.

ahhhhh ok. so can i get rid of it and just run the lines from the MC to the brakes? the arm is missing anyways. or has that been covered a billion times

I assume you mean that you want to run the new line from the front combo valve (looks like a proportioning valve) to the rear, not from the MC. :laugh3:
Simply skipping past the rear prop valve would cause the rear to have full pressure all the time, which can cause the rears to lock up prematurely. The best bet is to swap in an XJ prop valve into the front of your truck and run a brand new line to the rear axle. If I remember right, a rear ruber brake line from a Dakota is plenty long for the rear of your truck.
Jeep on!
--Pete

ComancheClub.com

stupidfast said:

ahhhhh ok. so can i get rid of it and just run the lines from the MC to the brakes? the arm is missing anyways. or has that been covered a billion times

Click to expand...

Without it your rear brakes will lock and skid easly.

alright i found bretts thread on it. thanks

stupidfast said:

ahhhhh ok. so can i get rid of it and just run the lines from the MC to the brakes? the arm is missing anyways. or has that been covered a billion times

Click to expand...

As I understand it (from someone else here on ) the adj prop valve in the back bleeds excess pressure back to the master cylinder. Supposedly if the front hyd lines fails, the MJ combo valve switches to providing full line pressure on this bleed line to send full line pressure to the rear brakes - instead of using the normal line. So capping the second line means no rear brakes if you break a front hyd line.

BTW, I just have the arm on mine held all the way up with a piece of wire. When I finish the brake swap I'll probably make a new link to connect it to the axle again as I expect too much braking in the back when I'm done. I have a relatively stock length one somewhere out in the garage if you want it.

I bypassed that with a line adapter and moved my brake hose to the back of the bracket for my SOA.

Remove it and use a XJ proportioning valve under the master cylinder, running a single brake line to the rear.

lawsoncl said:

As I understand it (from someone else here on ) the adj prop valve in the back bleeds excess pressure back to the master cylinder. Supposedly if the front hyd lines fails, the MJ combo valve switches to providing full line pressure on this bleed line to send full line pressure to the rear brakes - instead of using the normal line. So capping the second line means no rear brakes if you break a front hyd line.

BTW, I just have the arm on mine held all the way up with a piece of wire. When I finish the brake swap I'll probably make a new link to connect it to the axle again as I expect too much braking in the back when I'm done. I have a relatively stock length one somewhere out in the garage if you want it.

Click to expand...

I've never seen this specific system, but I've seen plenty like it, I DO NOT THINK IT WORKS THAT WAY.

To bleed excess pressure back to the master cylinder there would have to be a 2nd line running back to the master cylinder. I doubt there is one there.

The way most brakes systems work:

*The Master Cylinder has 2 stages (2 seperate pistons, one on top of the other inline), each piston powers half the brakes. Thats why there are 2 lines coming out the Master Cylinder.

*The Lines run to a combination valve, it has a pressure reducer (proportioning valve) for the rear brakes, and it merely splits the front brake line/pressure in two for 2 different brake lines running to the front brakes. As well, it has a sensor/switch between both brake stages, if pressure is lost on one of the stages, the pressure on the other side of the sensor/switch will move it and throw the switch. That will light your "BRAKE" light to tell you something is wrong.

*The Master Cylinder provides the redundancy to give you half your brakes if you have a leak or a failure in the brake parts. The Combination valve gives you the pressure reducer (proportioning valve) for rear brakes, a sensor/switch to tell if you lose half your brakes and lights a light to warn you and splits the front brake lines for 2 different brakes.

*For Vehicles that vary weight distribution greatly, like pick-up trucks and mini-vans, there is the additional proportioning valve in the rear before the line gets to the rear brakes. Its connected to the rear suspension to modulate the valve and vary the rear brake pressure/proportioning according to the weight distribution of the vehicle. These 2 proportioning valves have to work together, the 1st one has to be higher pressure than a normal proportioning valve and the 2nd reduces it further according to weight distribution. The 1st proportioning valve is different from other stock proportioning valves for other vehicle not equipped with a 2nd load varying proportioning valve. So you can't remove half the special system and expect it to work like the totally different system. You have to replace the whole system, with the other, that means replacing the combination valve (that has the proportioning valve in it) with an XJ (like suggested) and removing the 2nd valve and reconnecting the lines with a splice.

The redundancy in the brakes will work like it always has, wether you replace the 2nd proportioning valve correctly or not, the only problem will be, if you get the pressure reduction correct for the rear brakes.

The front Propo valve has a slier in it. if the front braks were to fail then it switches the rear brakes to the second circuit. The second circuit bypasses the rear load sensing propo valve and trips the brake light. This way when you lose the front circuit the rears get full pressure, regardless fo bed height. If you cut the second line then you need to join it into the hard line that goes to the axle. If you don't if the front fails you won't have any brakes.
SOme discussion:
http://comancheclub.com/forums/view...ht=propo&sid=3c738117e78ec38be3a54cdc8388fa50
http://comancheclub.com/forums/view...ht=propo&sid=3c738117e78ec38be3a54cdc8388fa50

there ARE 2 lines to the back in a Comanche!