bleeding brakes

[camanchedriver23]

i need to bleed my brake my pedal goes to the floor and my brake lights don't work util they go to the floor but when the truck is not running then i can pump them and get alot of pressure so i have heard i have to bleed all of my brakes at the same time is this true and can you take me through the steps so i do it right I'm not an idiot ive done it before i just never have on this truck and i havent usually can bleed one ata time so let me know asap please

[Eagle]

There's a special procedure for bleeding MJ brakes if you still have the rear proportioning valve in place. I posted the instructions awhile ago. I'd post the link, but I'd have to search for it and I have friends coming over, so I'll let you do the search. It's here ... somewhere.

[Drahcir495]

There's a special procedure for bleeding MJ brakes if you still have the rear proportioning valve in place. I posted the instructions awhile ago. I'd post the link, but I'd have to search for it and I have friends coming over, so I'll let you do the search. It's here ... somewhere.

Could you make it a sticky? How about a thread in the DIY forum? I can't find it. Thanks, Rich

[Eagle]

Yeah, the rear proportioning valve DOES require a special procedure. First, bleed all four wheels normally. After that, the FSM says to do the following:

After bleeding the brake calipers and cylinders the rear brake by-pass line must also be bled.

 

Open a front caliper bleed fitting and depress the brake pedal to the floor. This will shuttle the by-pass differential valve and allow fluid to flow through the by-pass line. The brake warning light on the instrument panel will illuminate when the ignition key is in the ON position. This signals the shuttling of the valve.

 

Re-Bleed the rear brake cylinders with the front caliper bleed fitting open.

 

After re-bleeding the rear brake cylinders the entire system must be bled again.

 

Bleed the brake calipers and cylinders in the following sequence:

 

1st -- Right rear

 

2nd -- Left rear

 

3rd -- Right front

 

4th -- Left front

[Drahcir495]

Yeah, the rear proportioning valve DOES require a special procedure. First, bleed all four wheels normally. After that, the FSM says to do the following:

After bleeding the brake calipers and cylinders the rear brake by-pass line must also be bled.

 

Open a front caliper bleed fitting and depress the brake pedal to the floor. This will shuttle the by-pass differential valve and allow fluid to flow through the by-pass line. The brake warning light on the instrument panel will illuminate when the ignition key is in the ON position. This signals the shuttling of the valve.

 

Re-Bleed the rear brake cylinders with the front caliper bleed fitting open.

 

After re-bleeding the rear brake cylinders the entire system must be bled again.

 

Bleed the brake calipers and cylinders in the following sequence:

 

1st -- Right rear

 

2nd -- Left rear

 

3rd -- Right front

 

4th -- Left front

Thank you for posting this information. I hope this corrects my lack of stopping power. - Rich

[Eagle]

Thank you for posting this information. I hope this corrects my lack of stopping power. - Rich

If you still have the rear height-sensing valve -- this won't help. The factory setup is biased to send virtually zero braking force to the rear wheels when the bed is unloaded.

[Drahcir495]

Thank you for posting this information. I hope this corrects my lack of stopping power. - Rich

If you still have the rear height-sensing valve -- this won't help. The factory setup is biased to send virtually zero braking force to the rear wheels when the bed is unloaded.

That sucks, I thought I had an answer. Is there a way to trick the valve into believing it has a full load? I zip-tied it up, but is still refuses to engage. I may just have to remove it :roll: .

[HOrnbrod]

If you still have the rear height-sensing valve -- this won't help. The factory setup is biased to send virtually zero braking force to the rear wheels when the bed is unloaded.

 

Not so with mine. Before I put disks on and the 96 booster/master, the bias w. the truck unloaded was about 75% front, 25% rear. I could lock up all four wheels (31"), although it required a lot of brake pedal pressure on my part. There is an adjustment procedure for setting the valve arm position in the FSM.

 

That sucks, I thought I had an answer. Is there a way to trick the valve into believing it has a full load? I zip-tied it up, but is still refuses to engage. I may just have to remove it.

 

Rich, the normal operating position of the valve arm is nearly parallel with the axle. Zip-tieing it pointing UP (if that's what you did) should make it worse. Tie the arm parallel to the axle and see if it helps. Or your valve may be shot internally, i.e. the diaphram may be gone. I don't think they are rebuildable.

[Eagle]

The problem with the FSM adjustment procedure is that adjusting calls for a new part (a spring, IIRC, but I'm not at home where I can confirm that), which is no longer available. In theory, adding load to the bed pushes the bed down which in turn pushes the arm on the valve up, so zip tieing it up at about 45 degrees should increase the rear brake bias. If it doesn't, the valve is probably not working.

 

The reason I don't trust them as I have posted previously, is that mine blew out in a panic stop situation. If one 20-year old diaphragm blew out, I have no reason to believe that another of the same device won't also blow out under panic stop conditions. I was lucky the first time -- I stopped before t-boning the old man who cut me off. I can't count on being lucky a second time.

 

The valves aren't available from Jeep, so the one that blew out left me with no choice. I had to bypass it, because it was hemoraging brake fluid. But -- I'm old enough that I grew up and learned to drive before they had such devices. The cars I learned to drive on routinely locked the rear brakes before the fronts in a panic stop. It's not a big deal to me, it's normal. I understand that it's unnerving for you younger lads who aren't accustomed to the phenomenon. But I still don't trust those old valves. I think it's a far better solution to dump the height sensing valve, re-plumb the hard lines so you have only ONE steel line from the front directly to the rear flex hose -- and then put a Wilwood adjustable proportioning valve in that one line to adjust the rear brake bias to suit your driving habits.

 

If you put the Wilwood valve in the driver's compartment, you can adjust it on-the-fly to compensate for carrying heavy loads. Or mount it right next the the front metering block, and you can adjust it by popping the hood for access.

[HOrnbrod]

The problem with the FSM adjustment procedure is that adjusting calls for a new part (a spring, IIRC, but I'm not at home where I can confirm that), which is no longer available.

 

I just re-read the level adjustment procedure in my 91 FSM - no spring involved in the procedure. Then I looked up the valve itself in the parts manual - there are two different valves. The 1990 and below (p/n 52002389) does have this external spring, so I assume this is what Eagle is mentioning. In 91 the valve changed (p/n 52005758) and there's no external spring. Another "upgrade" when the HO's came out? Taz, if you read this, are there any valves of either type left at some dealership?

 

The valves aren't available from Jeep, so the one that blew out left me with no choice. I think it's a far better solution to dump the height sensing valve, re-plumb the hard lines so you have only ONE steel line from the front directly to the rear flex hose -- and then put a Wilwood adjustable proportioning valve in that one line to adjust the rear brake bias to suit your driving habits.

 

If you put the Wilwood valve in the driver's compartment, you can adjust it on-the-fly to compensate for carrying heavy loads. Or mount it right next the the front metering block, and you can adjust it by popping the hood for access.

 

I agree, and if and when my valve goes bad, I'll either use the Wilwood valve, or better yet, since I'm basically a lazy bastid, replace it with a newer Toyota load sensing valve so I don't have replumb the lines. :D I want to keep the rear variable brake biasing capability since I haul loads frequently.

[camanchedriver23]

i ahve already removed the height sensor and re did all of that so does this mean that i can use the instructions on here

[Eagle]

i ahve already removed the height sensor and re did all of that so does this mean that i can use the instructions on here

If you already removed the height sensing valve, you don't need the instructions in this thread. You bleed as for normal brakes.

 

If you removed the height sensing valve, you should also have removed one of the two hard brake lines from the front of the truck to the rear. The single line you have left should run from the NOSE of the front brake metering block (not the bypass port underneath) directly to the flex hose at the rear axle.

 

Hornbrod -- I was not aware that they changed the height sensing valve in 1991. You are correct, my FSM is for the early style.

[Drahcir495]

Rich, the normal operating position of the valve arm is nearly parallel with the axle. Zip-tieing it pointing UP (if that's what you did) should make it worse. Tie the arm parallel to the axle and see if it helps. Or your valve may be shot internally, i.e. the diaphram may be gone. I don't think they are rebuildable.

That is what I did :oops: . I will give it a try your way and see that helps. Thanks, Rich

[mvusse]

On my truck, before the lift, unloaded the valve was horizontal, and the more weight I put in the back, the further the arm on the valve moved up.

 

I zip tied it about 60 degrees up and every time I hit the brakes the rears locked up. I now have it a little above level and the front and rear lock up at about the same time with the cap on the back and maybe 200 pounds of weight in it.

 

Need to get a longer rod so I can hook it up properly again.

[HOrnbrod]

On my truck, before the lift, unloaded the valve was horizontal, and the more weight I put in the back, the further the arm on the valve moved up.

 

I zip tied it about 60 degrees up and every time I hit the brakes the rears locked up. I now have it a little above level and the front and rear lock up at about the same time with the cap on the back and maybe 200 pounds of weight in it.

 

Need to get a longer rod so I can hook it up properly again.

 

Yes, normal no-load arm position for mine (before lift w. cap) was about 30-45 degrees above parallel. If you still have your old rod, you can pull the two end caps off and make a new longer rod from 1/4" stock. I just followed the bend contours of the old rod and extended the center section the height of my lift. The ends require a little grinding and filing so the end caps will snap back on and lock.

 

OR you can cut your old rod in half, thread each cut end, and insert a long 1/4x20 internally threaded hex standoff w. locknuts on each end like below and fine tune it to any length you want. Jeep should have put in an adjustable rod to begin with like other manufacturers' load leveling valves are designed.