MJ rear brake lines

I helped a friend work on his 87' shortbox MJ, and we ended up replacing line at the axle and both in and out of the proportioning valve because they would not come loose and were corroded badly.

There is obviously still air in the system as the unit worked reasonable before we messed with it, and now he has to pump it to get the brakes to grab.

We have no air coming out of the system at the rear brakes, and up to the splice we had to install at the return line.

My questions are:

Where exactly does the return line go.

Is there a special procedure for bleeding MJ brakes?

return line?
main line comes back to the weight/height valve, splits into two- one per wheel.....you have a return line?

always remember- anytime you break open a line and loose all the pressure, you have to reset the proportioning valve- instead of useing the tool- that mysterious tool that few of us have seen, but we know exsists- reset is simple-if you weigh enough-

go get in the vehicle, put both feet on the brake pedal- and stand on it.
hard.Dont seat in the seat and push- get ON it and STAND on it hard-
listen for a click noise- when you hear that click, the piston has moved over the oriface, pressure is now full at 70/30 instead of 90to100% front only-

your basicly trying to overcome spring pressure inside the Master- do it once, you`ll laugh.

I dont have a return line on my old MJ..I feel....left out.

Yes there is a special bleeding procedure. You need to get the air out of the return line from the rear load-adjusting valve to the front valve. Have a look at these threads.

http://www.naxja.org/forum/showthread.php?t=9679
http://www.naxja.org/forum/showthread.php?t=24821

I've got Crown Vic disks on the rear of my MJ. I just tied the arm on the rear valve up to get max pressure. I have a 97 double diaphram booster/mc/propvalve that I plan to install this spring. I will probably ditch that rear valve in favor of a wilwwod adjustable valve.

Ed in North Ga. said:

return line?
main line comes back to the weight/height valve, splits into two- one per wheel.....you have a return line?

Click to expand...

On mine, the feed line goes to the rear valve. The output of that rear valve goes down to the axle and feeds the brakes. There is a return line to the prop valve up front. I think it The MJ prop valve is different than the XJ prop valve and has an extra connection.

I'm not sure how the second line works. I understand that the front valve sends pressure down this line so that the rear brakes get full pressure if the fronts lose pressure - ie "bypassing" the prop valve. http://www.naxja.org/forum/showthread.php?t=82708

That line is ther if the front loose pressure the rear will get full presure.

I knew someone here would have an explaination.

Thanks!

Ron

I replaced the stupid valve in mine with a joiner and capped off the return line. With 6" of lift, it made me feel like I had zero brakes at the WORST times!