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:nuts: Mayday! I can't stop and can't seem to figure out what is wrong. Can anyone bail me out on this? 90 Comanche which I removed the rear height proportioning valve. Replaced the front calipers, master cylinder and booster! I researched all the great info on this subject and assumed the rear proportioning valve was originally at fault, or at least partly at fault, since I have 280K on my machine and I have never replaced the rear shoes! Yes, I bought the truck new so I know the rear shoes are original. Then, about two weeks ago, the front calipers started draging real bad and the wheels were buring hot so I figured the calipers needed replacing. Lord help me, this only seemed to create more problems and the brake pedal would go completely to the floor no matter how much I bled the lines. Anyways, I replaced the master cylinder and booster, but to no apparent avail! Now I do realize there is air in the line, but here is the crazy part, you bleed the system as normal but the brakes still keep going to the floor, so then, if you reverse the proceedure and go from the last place, the left hand front, and go back to the right front you get a blast of air, but only once. I am going to the junk yard to get a cherokee front porportioning valve. The only other thing I can think of is that the replacement calipers are somehow responsible, or, more likely, that stupid front proportioning valve has been the problem all along. Ideas anyone? :bowdown:

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so you were having brake problems before you started changing the stock braking system?

 

Is there any sign of leaking fluid anywhere along a hardline?

 

Do you lose fluid after a series of compressions?

 

Do you have some braking power or none at all? I.E. if you jack up a tire, spin it, then hit the brakes, does it stop? Is it a firm stop or just barely got it to stop? Might be good to try at all four corners.

 

When you bleed the brakes the normal way (from furthest away from the master cylinder to the closest), do you get fluid coming out of each bleeder?

 

I honestly think its a bad idea to just start replacing things unless there is a reason to do so, likely it will just cause more problems and cost you more money. Figure out what is wrong first.

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Thanks for the response. Not a brake expert by any means, but not a novice either. There are no leaks, no fluid dripping any place, and, yes, I am getting good flow through all four points. Is it possible I just need to keep bleeding on one point, the right rear, until I am sure that I have completely run all air out of that line? I just can't believe that I am not getting any brake pedal pressure build up. I've bled the heck out the the thing. I'll try the tire stop test on the rear, but the front calipers hold well. I've never run in to this sort of problem before, but then I've never had a machine with such a fubared system. It seems to be acting like some one way valve that lets air in the system.

While I agree about just replacing parts, it all seemed reasonable and logical to begin with, and with so many miles and years on the truck I figured I screwed up on the caliper replacement, but obviously the master cylinder had to be the problem and the booster failed an air tight test. Now, I just don't get what could be going on, or could be going on, however I imagine I'll eventually prevail.

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Ok, I went and checked to see if there was any change in the fluid level after pumping the brakes. There was no change in the fluid level. I must still have air in the lines? :mad: Sound about right? There is no evidence of any leaking any place. With a new master cylinder and booster, along with new calipers and the removed rear height proportioning valve, I can only think there must still be a large amount of air in the system. :eek:

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I had front calipers dragging excessively, like almost locking up.

I had rear brake shoes which have been on the truck since new, and still look new, so they have not been doing anything for the last 280K miles.

So, yes, I have been having some kind of substandard braking for quite some time.

 

Well, I figured that the reason the rear shoes were not wearing was because of this proportioning valve in the rear. I had researched the many problems this valve could cause here on ComancheClub.com.

When the truck was new it had excellent stopping power, but this had been missing for many years. I elected to eliminate the valve after I found that replacing the front calipers had not solved my brake problem.

I reasoned that elmination of the rear proportioning valve would only simplify the possible reasons for why the front brake calipers had started causing problems to begin with. I thought that maybe the rear valve was leaking and all the braking energy was being transfered to the front brakes, but in either event the rear brakes simply had not been doing anything for the last seventeen years and I thought it was about time the damn things started doing something, ah, like helping me stop.

 

As I understand it, a fault in the rear brake system would route the total braking power to the front brakes, or vise versa.

Obviously I did not think this through and just assumed the front calipers probably just needed replacing when I started this project. However,...

After replacing the calipers I throughly bleed the lines, but just could not seem to get all the air out at the rear bleeders. I reasoned that the rear proportioning valve was somehow allowing air in while able to hold brake pressure, acting as a kind of one way valve. These valves seem to have many potential ways to fail, so I elected to just elminate it. This reinforced my notion that this is why the front calipers were dragging. I

conduced an air tight test for the booster and found it had seemed to have failed while doing all this bleeding. I felt that it was probably time to just go ahead and replace the master cylinder and brake booster. I thought, this would also elminate any other potential problems and the brake system should then function like any normal brake system.

My only modification was as described by Eagle who eliminated his rear proportioning valve after it blew up in a panic stop. I disconnected the front bottom line on the front proportioning valve and caped it off. I did the same at the back for this same line at the T fitting. The brake line which used to feed the rear porportioning valve was disconnected and reconnected to the T where the bottom line of porportioning valve once went up to. The original hard line that connects to the flex line was left intact. That's it, I see no leaks or loss of fluid. Any idea how much brake fluid it takes to fill rear brake line?

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As I understand it, a fault in the rear brake system would route the total braking power to the front brakes, or vise versa.

Not exactly.

 

The front and rear circuits are independent. If you lose the rear brakes, you will still have front brakes, but they will only provide as much braking as they did before (which is probably about 60% to 75% of the total in a 100% functional system).

 

If you lose the fronts, though, it gets sticky. In the MJ, the front combo valve does NOT perform any proportioning. Proportioning is all handled by the height/load sensing valve at the rear. However, the front metering block DOES include a bypass feature so that if you lose the front brakes, the rear proportioning valve is bypassed and you get full braking to the rear wheels. That's not great, of course, since the rear wheels only contribute a small portion of the total braking force, but at least you get all of that portion.

 

However, when I sliced and diced an MJ front metering block to see how it works internally, I was dismayed to find that the bypass passage was not drilled through. In other words, the vehicle that valve came from would NOT have had any bypass function if the front brakes had failed.

 

I plan to simply eliminate the proportioning valve, plug the outlet in the from metering block that goes to the bypass circuit, and route the hard line direct from the normal outlet for the rear circuit to the flex hose on the rear axle. Under some conditions that may result in too much braking at the rear, but I grew up and learned to drive years before they had proportioning valves, so I think I can deal with that better than I can deal with only having front brakes.

 

You said you put in a new master cylinder? Did you bench bleed it first?

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First of all, yes, every thing you did, was worth it, with 260K, I would think your 2x past the rebuild time.

 

The reason your rear brakes were not working, they were not adjusted properly, thru the "self adjusters" that need to be manualy adjusted. This should be checked ever 6 months, or when the braking power is lost. That's why you got 260K on the original brake shoes. After the self adjusters failed, the shoes were not making contact to the drum. This should have been notice on your parking brakes also.

 

Did you pull a rear wheel, and check if the wheel cyl is leaking, or even working?? It a $12 part that worth changing out, and do both of them.

 

My only modification was as described by Eagle who eliminated his rear proportioning valve after it blew up in a panic stop. I disconnected the front bottom line on the front proportioning valve and caped it off. I did the same at the back for this same line at the T fitting. The brake line which used to feed the rear porportioning valve was disconnected and reconnected to the T where the bottom line of porportioning valve once went up to. The original hard line that connects to the flex line was left intact.

 

I think you got some thing run wrong in the rear, You did the front proportioning valve correct, but then you only need one hard line to the rear, from the front port, direct to the soft line in the rear, I don't get it where you "reconnected to the T" If you deleted the rear porp valve, just let the line hang, as you disconnected it up front, and then remove the tee completly, and the one hard line should be connected directly to the soft line ( to the rear axle)

 

If you have 2 hard lines connected in the rear, you could be sucking fluid back to the front porp valve when your trying to bleed the system, Or you have the wrong hard line hooked up to the front porp valve, front port.

 

If you replaced the master cyl, did you bench bleed it first?? Or just install it, and hope to get the air out thru about 20 bleeds?? It could be air locked if you did not bench bleed it first.

 

As I was typing this out, Eagle was posting :bowdown:

And before I get yelled at, Yes, the front porp valve is the "Metering Valve/Block"

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Well, thank god I listened to my friends about going to ComancheClub.com

 

Ok, tomorrow I'll just run the supply line to the flex hose. I thought about just doing that to begin with but didn't want to fight any more brake line fittings.

 

Yes I bleed the system per the instructions, which says not to bench bleed since over stroking could damage the master cylinder.

 

Instead I installed the new booster and master, bleed the master by simply putting my finger over the disconnected lines on the return stroke.

Pretty sure that the master is successfully bled.

 

I'll try connecting the rear brake line directly to flex, like the rest of you, and report back.

 

Now I thought someone said that by directly connecting up the rear line this way would result in full energy being directed to the rear brakes. Meaning the full measure of the rear brake master. That 30 or 40% you were mentioning. Is this correct?

 

Thanks.

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:nuts: Mayday! I can't stop and can't seem to figure out what is wrong. Can anyone bail me out on this? 90 Comanche which I removed the rear height proportioning valve. Replaced the front calipers, master cylinder and booster! I researched all the great info on this subject and assumed the rear proportioning valve was originally at fault, or at least partly at fault, since I have 280K on my machine and I have never replaced the rear shoes! Yes, I bought the truck new so I know the rear shoes are original. Then, about two weeks ago, the front calipers started draging real bad and the wheels were buring hot so I figured the calipers needed replacing. Lord help me, this only seemed to create more problems and the brake pedal would go completely to the floor no matter how much I bled the lines. Anyways, I replaced the master cylinder and booster, but to no apparent avail! Now I do realize there is air in the line, but here is the crazy part, you bleed the system as normal but the brakes still keep going to the floor, so then, if you reverse the proceedure and go from the last place, the left hand front, and go back to the right front you get a blast of air, but only once. I am going to the junk yard to get a cherokee front porportioning valve. The only other thing I can think of is that the replacement calipers are somehow responsible, or, more likely, that stupid front proportioning valve has been the problem all along. Ideas anyone? :bowdown:

 

When you replaced the calipers did you put the correct caliper on the correct side? I have seen this done before and they will bleed and everything seems fine, but the brakes never totally bleed correctly and the brakes are spongy. The bleeders are supposed to be at the top on the back of the calipers not on the bottom. If the bleeders are on the bottom you have the calipers on the wrong side. Also your front brake hoses could be bad not allowing you to bleed the brakes correctly. They go bad inside and come apart and restrict the flow and act almost like a one way valve allowing fluid to flow one way, but not the other. If the hoses are old and cracked I would replace them just for safety.

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1986Comanche brings up a very good point on the old soft lines being deteriorated, I know I've had this problem of a Ford van, and just replaced all of the flex lines and solved some problems.

 

I assume your hard lines are in good condition? If there is any rust, I would not trust them, and replace the steel lines also. The couple of MJ's that I've redone, I just tear out all of the steel lines and flex lines and replace every thing with new, the time involved is time saved messing with it latter. Note- all of the steel lines are 3/16".

 

But on the other hand, I'm in the rust belt, and working on these 20 year old trucks, everything is just rotted out, so new lines are the norm.

 

Any steel lines that you modify, just make sure you double flair and use the correct fittings, yes, I know other's have used compression fittings, but they are not kosher.

 

Now I thought someone said that by directly connecting up the rear line this way would result in full energy being directed to the rear brakes. Meaning the full measure of the rear brake master. That 30 or 40% you were mentioning. Is this correct?

 

Some people have had problems, but I done a '89 last year that is a driver for me, and I have no problems with this, I've had some panic stops, and the front lock up on me. And yes, it's better to have the fronts lock up and have some controll over a skid.

 

Well, thank god I listened to my friends about going to ComancheClub.com

 

You must have some Good Friends :D

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:bowdown: Well, I I believe 86Comance has solved this idiots poblem.

In his haste to replace the brake calipers it appears he did put them on the wrong sides, which does put the bleeders on the bottom, and this does make it difficult to remove all the air.

 

Considering the grevious oversight already mentioned, I decided to avoid further errors by directly routing the rear brake supply line to the flex hose. As recommended.

 

All brake lines are in in excellent condition so I will go with them for the time being. Owning the vehicle since new has the great advantage of having been well taken care of. Apparently the only real flaw has been with the owners belief in his supposed mechanical knowledge. :oops:

 

Now, I have to go out and swap the calipers and rebleed the brakes. I have little doubt that success is in sight.

Thanks to all, and I'll report back on the results shortly.

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Ok, Well, I got brakes and I have eliminated the dreaded explosive Eagle Valve. Thanks to everyone for their contributions. Special thanks to 86Comanche :bowdown: . Well I have offically joined the ranks of the Idiots who routinely outwit the fool proof designers. Lord, how embarassing, what next? Stay tuned for more humor at my expense. :brows: Oy yes, he says; "Not a Novice Either." Ha!

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Ok, Well, I got brakes and I have eliminated the dreaded explosive Eagle Valve. Thanks to everyone for their contributions. Special thanks to 86Comanche :bowdown: . Well I have offically joined the ranks of the Idiots who routinely outwit the fool proof designers. Lord, how embarassing, what next? Stay tuned for more humor at my expense. :brows: Oy yes, he says; "Not a Novice Either." Ha!

 

Well, I'm glad the info helped and that you got your problem worked out. That's why we're all here, to help other Comanche owners out.

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Yea, glad to hear that it was just a minor mistake and that it all worked out to be a easy problem to solve :D

 

But don't beat your self up on this :wall:

 

I think that's in one of the 3 Rules on this board ;)

 

And your friends were right to drop in and ask what could be the problem, other wise you would still be trying to torch, ah....er, trying to fix the dang thing.

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Ok ok guys this guy just saved my a$$ some time and money.....will he would have if this was talked about a week ago :oops: O well. So here is the thing I was having brake issue to and thought it was air in the line and then it went to the bake booster so I bought a new to me 99 Cherokee off of eBay wrong year. The rod was to long :oops: So when I got home at 3:00 in the morning from work I thought what the hell it really could not be that the caliber were on the wrong side will guess what they were. So at 3:30 I changed the brake caliber then went in and tried to wake the wife up at 4:00-4:30 to go out and bleed the brake. That was not going to happen :mad: so when she gets up around 8:30 she went out and bleed the brakes. Now my truck stops. :D So guy your not the only one that did not no that these damn thing can go on the wrong side but leave it to the Comanche guys to figure it out. :bowdown: :cheers: :bowdown:

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