Brake Bleeding

Guys, whats the bleeding procedure on an '89 with the rear proportioning valve in the system? I plan to bleed the whole system to get fresh fluid in the fronts also.

If your rear Por'ing valve is still working, it's not a problem, fluid will just flow thru it.

But first thing, jack up the rear and adjust the "self adjuster" in the rear shoe, this will solve alot a probems with the whole system. Just set them so the wheel "drags" alittle when you spin it by hand.

Then start with the wheel furthest from the master cyl, the right rear, next the left rear, right front, and finish with the left front.

I do the one man bleading way, using a 1/4" rubber hose, attached to the bleader and in to a bottle/jug with brake fluid in the jug, tube has to be in fluid, keeps air from sucking back into the system.

Pop master cyl cover off, and leave off, open bleader, with hose on, into jug, pump 10 times, close bleader, move to next wheel and check fluid level in master, keep toped off, don't let the master get dry.

And pump the brake petal all the way down, and all the way up, slow, with the motor off.

And if all of your bleaders open with out a problem, in 15 minutes your done.

Any fluid you pump out, do not reuse, toss it, Or keep it for the next time to keep the hose in fluid. And start with new fluid in the bottle to start if you need to. A clear soda bottle with a screw on top works good.

And Happy :wrench:

Thanks, I was wondering if the rear valve required any special precedure. Hopefully, tomorrow I'll have the new brake lines in and working brakes again.

Then, fix the alternator. :(

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

to me, that

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l l

l l

means remove rear brake prop valve and replace with xj valve.

that's just too much crap to bleed.

to me, that

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/ \

l l

l l

 

means remove rear brake prop valve and replace with xj valve.

 

that's just too much crap to bleed.

I agree. The wisdom of dumping the rear height-sensing valve was brought home to me when I lost my brakes as a result of a panic stop when I was cut off by an errant senior citizen (more senior even than me, if you can imagine that). Not only did the rusty hard line pop over the gas tank, the rear valve also exploded.

Now I don't trust them. At all.

Damn!!! that would suck so bad!!! that reminds me of when my clutch went out for some reason... :nuts:

well that sounds like a wonderful crusade :D

haha, we're all glad you're here to keep us in check Eagle...remember that 86 "dana 44" my dad had? well guess what, both he AND I were WRONG. it's an amc20.

Ok, if I use an XJ prop valve, what size line do I need to run to the back? The hose to the axle takes a 1/4" line. XJs the same?

Eagle - Thanks for the update on the rear Porp'ing valve......Main reason to cut the non-working valve off to begin with ;)

And you know that the line will alway blow out in some obscured location

Eliminator89 - The rear brake lines are totally diffrent from the XJ. By hose, do you mean the soft line from the frame to the axel? That is also diffrent, and the swb and the lwb are two diffrent soft lines, I always replace with the swb line ( a little longer and $5 less)

And with a rear lift, the Dakota soft line will work.

All of the hard lines (steel lines) are 3/16" tubing, not 1/4"

And to convert to the XJ front porp'ing valve check this out -

http://comancheclub.com/forums/viewtopi ... ting+valve

A timeless topic ;)

Ok, so I can use the existing valve, just plug the port under the front and use the front facing port?

This would be nice. No junkyard crawling for an XJ valve. I have a short bed 2 wheeldrive. The hose to the axle is in good shape and I plan to re-use it. New line will be run from the front prop valve top the rear of the truck. I had planned to re-use the rear prop valve but advice here is to eliminate it. I don't carry heavy loads so it should not be a problem.

3/16"? looked like 1/4" to me. I'll take a peice to the parts house to compare and be certain I get the correct size.

I had planned to re-use the rear prop valve but advice here is to eliminate it. I don't carry heavy loads so it should not be a problem.

Actually, it may be a problem precisely because you don't carry heavy loads.

When you eliminate the rear height-sensing valve, you get full braking force to the rear wheels at all times. When a pickup is unloaded, the back is quite light and heavy braking or panic stops usually result in the rear brakes locking up long before the fronts. The purpose of the valve is to reduce the amount of rear braking when you're running light, and to give you full brake power to the rear when you're loaded down.

This is a non-issue for me because I'm an olde pharte who grew up and learned to drive a couple of decades before they invented proportioning valves. I expect the rear brakes to lock and the vehicle to try to switch ends on me under some conditions, so it's not something new, different, and scary.

Those of you who have never gone through a brake-induced spin-out should take this into account. Under most conditions it'll never be a problem. Where it could be a problem is rain, snow/ice, and when you're heading down a steep hill so that even more of the vehicle weight is on the front wheels rather than the back. A true panic stop isn't an issue because when you REALLY stomp on the brakes all four wheels lock up. At that point you're no longer driving, you're just along for the ride in a pre-aimed cruise missile. (No, you really can't steer when the front wheels are locked up. Trust me on that.)

Try it with the rear valve out of the circuit, but drive easy until you know how your brakes are going to act. And if you're a really heavy-footed driver I would suggest that you do this only in conjunction with a Mopar or Wildwood adjustable proportioning valve in the rear brake circuit.

For the rest of us, and especially if you're due to freshen up the rear brakes anyway, a partial offset is to look for rear wheel cylinders that have the same length as the factory ones but a smaller piston diameter. If your axle is a D44 this is easy -- buy wheel cylinders for the D35. They're smaller. Using smaller diameter wheel cylinders reduces the amount of force actually transmitted from the hydraulic circuit to the brake shoes. It's not perfect, but it helps.

Eagle...remember that 86 "dana 44" my dad had? well guess what, both he AND I were WRONG. it's an amc20.

Is this where I get to say "I told you so," or didn't I told you so?

There is NOTHING wrong with an AMC Model 20 axle. It's a huge, beefy axle that has been used reliably for many years in vehicles much larger and heavier than the MJ. The only problem with it is weight and ground clearance.

hehe, i just wanted to bring that up and say i appreciate your knowledge

Back to swapping in an XJ proportioning ("combination") valve.

Somewhere on this forum, a long time ago, I or Pete posted a photo I took of an MJ front metering block (I'll call it that since it doesn't have any proportioning function) that I sliced in half to be able to see how it worked internally. It was that exercise that showed me the "extra" rear brake line for the MJs isn't a "return" line, as I had always been told (even by the techs at the dealership), but an emergency by-pass line. It was a worthwhile sacrifice.

I haven't got a photo, but since doing the MJ combo valve I have more recently sliced up an XJ combo valve. And having done so, I still cannot figure out just what it's supposed to do. The best I can figure, what it actually does seems to be that it prevents any fluid from getting to the rear brakes until you really stomp on the brake pedal ... at which time it would allow full pressure to the rears.

That's the only way the spings and plungers and O-ring inside the thing can work, but it doesn't make any sense to my understanding of what a brake proportioning valve is supposed to do -- which is limit the pressure to the rear under conditions that might cause a spinout if the rear brakes lock up before the fronts. That doesn't happen under normal driving -- it happens under heavy braking and in panic stops.

The other problem with XJ combo valves is that they get gummed up internally. I know of numerous people in NAXJA who found they had NO rear brakes. My own '88 XJ is that way -- if I stomp on the brakes in snow, the fronts lock up and the rears keep rolling. One of these days I have to open that combo valve up and either clean it out, or just gut it.

For that reason, although I've explained the downside to keeping the MJ combo valve and removing the rear height-sensing valve, I also don't see swapping in an XJ combo valve as much (if any) of an improvement. Personally, I would rather know that I have rear brakes, and then deal with how to limit the rear braking force if the rear wheels lock up too much. I can deal with too much rear brakes a LOT better than I can deal with no rear brakes. I have a box on my bench with 5 XJ combo valves in it and one MJ combo valve. Those 5 XJ valves are NOT slated for installation in any of my MJs.

Well, I done it. I replaced the rusted lines with a single line straight to the hose to the rear axle. Replaced both axle lines and one wheel cylinder. I removed the line at the prop valve that attaches underneath and plugged the port. Attached the new line to the front port.

I now have brakes again. 8)

I see I need to rebuild the rear brakes but they'll do for now. The hardware is a bit rusty but they are working.

Now to fix the alternator. It isn't alternating.

Let a truck sit idle for a couple years and it goes to pot. :cry:

Brakes are a good thing.

You can take that to the bank.

hey where is this thing located can i have a picture of it i don't like how you guys are telling me stories of brakes failing and I'm going on a trip through a canyon and a 14 mile steep hill and tons of switch backs

It's just above the rear axle, on the left side of the differential. There should be (but very possibly won't be) a round rod connecting a lever arm on the proportioning valve to a ball stud on the differential. If that rod is NOT there ... someone else has been mucking around with your brakes and you have zero idea what's going on with them because you won't know what the previous mucker around has done.

I agree with you Eagle. I am from the old school, before the invention of the proportioning valve. So I expect the rear brakes to lock-up. That's why this height proportioning valve is confusing to bleed. :nuts: Thanks for the correct proceedure in bleeding a system with a height sensing proportioning valve. Well; I going to properly bleed my entire brake system now, thanks to you :D

so I'm gunna be a :dunce: here . so i can take the prop valve completly pu of the system if i want and just comtine the lines straight to the rear axel? and i will just make my rear breaks mor jumpy?

Eagle,

what do you suggest in place of the stock valve?

cap the return line at the front block and run the feed line to a T?

Pete - how do you center the proportioning valve so the light on the dash will go out, after bleeding the brakes for the second time around? - meaning with the front bleeder open so the shuttle the valve will travel to one side, while rebleeding the rears. :help:

Eagle,

 

what do you suggest in place of the stock valve?

 

cap the return line at the front block and run the feed line to a T?

It is not a "return" line. It's bypass line. I recommend removing the second line completely. If you leave it there, you have twice as much brake line under the chassis, corroding away and waiting for the most inopportune moment to spring a leak. Plug the forward outlet on the bottom of the front distribution block, and run ONE line from the "nose" out let of the front distribution block directly to the rear flex hose.

If that makes the rear brakes too touchy for you, I would suggest getting a Wilwood adjustable proportioning valve from Summit Racing or from Mopar Performance and putting that in the line to the rear. The only drawback is that it doesn't automatically adjust as you add weight to the bed. If you frequently alternate between heavy loads and running empty, you could re-route the line through the cab and mount the Wilwood so the knob can be reached from the driver's seat.