Soft brake peddle cause

[MT Mike]

Pedal pedal pedal pedal pedal pedal pedal pedal pedal pedal pedal pedal pedal pedal pedal pedal pedal pedal pedal pedal pedal pedal pedal pedal pedal pedal pedal pedal pedal pedal pedal pedal pedal pedal pedal pedal pedal pedal pedal pedal pedal pedal pedal pedal pedal http://grammarist.com/usage/pedal-peddle-petal/
Morons :badpc:

 

[dan1977p]

I have seen no reason to replace the combo valve on mine, which would require me to make new steel lines and figure the tooling out out due to the lack of space to get at it, since mine works and does not leak. I researched the combo valve internet wide and decided it could not be the problem based on test data I have. No one has reported fixing a mushy peddle with just a new combo valve. They have replaced them when they seized up and fluid only flowed to one set of brakes. All 4 of mine work fine. Gush have a gutless soft as water peddle.

The thing in bold has been reported twice on this thread alone as being a fix or at least helped and now another report of a combo valve leaking that was previously missed as an issue because people just assume that block with a spring and a few holes drilled in it can't go bad.

The way your problem has been reported has only three possible root causes, in my opinion (ordered most likely to least likely): Air in the system, water in the system, leak in the system.

I would rule everything else out because you have a solid pedal with the jeep off and when the vacuum booster is engaged, it gets soft. It also seems to get better after some random part was changed and then a few days later another random part gets thrown at it and it gets worse again. That just screams to me that the system gets opened up and air is introduced or a fitting is now loose causing a leak.

Water is a very real possibility in the combo valve if there was ever any sludge in the system. My brake fluid looked like it had never been changed and the amount of black sludge I cleaned out of the master cylinder was impressive. I dumped a bunch of brake cleaner down the lines and cleared out a ton more but still had a soft pedal, went through almost all the same things mentioned in this thread and still the same. The only things not replaced were the drums, combo valve and hard lines. Lo and behold, replacement of combo valve with one I took apart and cleaned and the lines going to it from the MC solved my problem. You could pop the end caps off and clean it while still connected pretty easily.

 

[Ecomike]

"end Caps" is plural, where is the other end caps(s) on the combo valve?. All I ever saw was the one I have bleed on the front with many quarts of new brake fluid out of. This system has always been clean for over 12 years and never gave me a bleding problem before. Probably bleed and filled it with 10 gallons of new Dot 3 brake fluid. No sludge, never has been. But I hear you. Also had this mushy peddle for 3.5 years, till the 2nd new AZ MC seemed to have failed and got replaced with no change, then found a bad 3-4 old AZ wheel cylinder leaking air in but not fluid out. Never had any brake fluid loss in the MC reservoirs the last 3-4 years until one day late last year when one wheel cylinder must have suddenly leaked and let air in (found later to be a source of air in getting in after bleeding), but it stopped leaking fluid disguising the problem as an MC being bad so I replaced the MC again, first. 4 MC's ago I had a 12 month old (not rebuilt, was new) MC fail in about 6-12 months out the rear and it wiped out the almost new (1-2 years old) Vacuum booster leaking brake fluid into the booster. The Booster suddenly started hissing noticeably and the MC was loosing fluid. So I replaced both at the same time with new AZ parts. I do not recall the Combo valve being reported as a fix for working brakes with a mushy peddle, just as a fix for non working brakes, like no rear brakes with good front brakes. Someone said that was typical problem with a combo valve as I recall? A stuck valve blocking flow to one set of brakes. I do not have that problem. I also recall trapped air in the combo valve being reported which is why I started for the first time on any of my jeep brakes in 14 years to bleed the combo valve first and again last when bleeding the brakes on my 5 jeeps. And that did help on this one jeep!!!

The thing in bold has been reported twice on this thread alone as being a fix or at least helped and now another report of a combo valve leaking that was previously missed as an issue because people just assume that block with a spring and a few holes drilled in it can't go bad.

The way your problem has been reported has only three possible root causes, in my opinion (ordered most likely to least likely): Air in the system, water in the system, leak in the system.

I would rule everything else out because you have a solid pedal with the jeep off and when the vacuum booster is engaged, it gets soft. It also seems to get better after some random part was changed and then a few days later another random part gets thrown at it and it gets worse again. That just screams to me that the system gets opened up and air is introduced or a fitting is now loose causing a leak.

Water is a very real possibility in the combo valve if there was ever any sludge in the system. My brake fluid looked like it had never been changed and the amount of black sludge I cleaned out of the master cylinder was impressive. I dumped a bunch of brake cleaner down the lines and cleared out a ton more but still had a soft pedal, went through almost all the same things mentioned in this thread and still the same. The only things not replaced were the drums, combo valve and hard lines. Lo and behold, replacement of combo valve with one I took apart and cleaned and the lines going to it from the MC solved my problem. You could pop the end caps off and clean it while still connected pretty easily.

 

[dan1977p]

The firewall side of the combo valve has the spring in it and has an adapter for, I think, the right front brake. On the GC valve, it was capped off and I suspect the front brakes were t'd after the combo valve.

 

[Ecomike]

I got some work done on this the last 2-3 days, after my last cataract eye surgery (I am no longer blind )party1:
I looked at a spare combo valve and I suspect that the front and rear sides of the combo valve's fluids do NOT communicate liquid to liquid with each other? Also the combo valve sensor does not have a seal or o'ring on the thread side to keep fluid from leaking where it threads in!!!!! NO way it can seal 4000 psi high pressure brake fluid, so the seals must deeper inside the valve. Seems like there is a cam like valve body inside the outer body that slides in either direction to trip the switch when the front or rear side looses pressure.

Is this right? If so then there is no reason to bleed the rear brakes after only replacing a front caliper or front hose.

The thing in bold has been reported twice on this thread alone as being a fix or at least helped and now another report of a combo valve leaking that was previously missed as an issue because people just assume that block with a spring and a few holes drilled in it can't go bad.

The way your problem has been reported has only three possible root causes, in my opinion (ordered most likely to least likely): Air in the system, water in the system, leak in the system.

I would rule everything else out because you have a solid pedal with the jeep off and when the vacuum booster is engaged, it gets soft. It also seems to get better after some random part was changed and then a few days later another random part gets thrown at it and it gets worse again. That just screams to me that the system gets opened up and air is introduced or a fitting is now loose causing a leak.

Water is a very real possibility in the combo valve if there was ever any sludge in the system. My brake fluid looked like it had never been changed and the amount of black sludge I cleaned out of the master cylinder was impressive. I dumped a bunch of brake cleaner down the lines and cleared out a ton more but still had a soft pedal, went through almost all the same things mentioned in this thread and still the same. The only things not replaced were the drums, combo valve and hard lines. Lo and behold, replacement of combo valve with one I took apart and cleaned and the lines going to it from the MC solved my problem. You could pop the end caps off and clean it while still connected pretty easily.

 

[Digger87xj]

I got some work done on this the last 2-3 days, after my last cataract eye surgery (I am no longer blind )party1:
I looked at a spare combo valve and I suspect that the front and rear sides of the combo valve's fluids do NOT communicate liquid to liquid with each other? Also the combo valve sensor does not have a seal or o'ring on the thread side to keep fluid from leaking where it threads in!!!!! NO way it can seal 4000 psi high pressure brake fluid, so the seals must deeper inside the valve. Seems like there is a cam like valve body inside the outer body that slides in either direction to trip the switch when the front or rear side looses pressure.

Is this right? If so then there is no reason to bleed the rear brakes after only replacing a front caliper or front hose.

Correct.


The switch does not need a gasket as that portion of the combo valve does not see fluid.
As long as the pressures are equal, the piston is centered & the light is off.
If one side loses pressure, the piston slides to the low differential and a resulting high spot in the piston grounds the switch.

Its purpose is to separate the brake circuits so if there is a leak in one, you do not completely loose all braking.

Also correct that typically you only need to bleed the circuit you are working on, and in the front, most times only that wheel.

 

[Ecomike]

I never liked that plastic switch, if its leaking replace it. For a fast check I'd try taking out the switch & installing a plug in its hole to see if the pedal feel improves.
PS: Is there any type of sealer that can be used under that switch that brake fluid won't destroy?

I just inspected a spare JY combo valve and it looks like there is no brake fluid contact at the switch, unless the internal seals of the valve itself are bad???? There is no seal at the switch itself!!!!

 

[Ecomike]

Awesome, I got that part right finally. Could have saved a lot of time if I had know that earlier.

Correct.


The switch does not need a gasket as that portion of the combo valve does not see fluid.
As long as the pressures are equal, the piston is centered & the light is off.
If one side loses pressure, the piston slides to the low differential and a resulting high spot in the piston grounds the switch.

Its purpose is to separate the brake circuits so if there is a leak in one, you do not completely loose all braking.

Also correct that typically you only need to bleed the circuit you are working on, and in the front, most times only that wheel.

 

[Ecomike]

Now that I understand this, do you see any reason to bleed the rear of the combo valve (which is a pain to even reach, not sure it is possible) to get rid of trapped air in the front brake lines or just bleed at the calipers?

I never had to bleed a combo valve before to get rid of air, but I have been bleeding the front lately out of desperation....

Correct.


The switch does not need a gasket as that portion of the combo valve does not see fluid.
As long as the pressures are equal, the piston is centered & the light is off.
If one side loses pressure, the piston slides to the low differential and a resulting high spot in the piston grounds the switch.

Its purpose is to separate the brake circuits so if there is a leak in one, you do not completely loose all braking.

Also correct that typically you only need to bleed the circuit you are working on, and in the front, most times only that wheel.

 

[Digger87xj]

I've never needed to. I don't think air can get trapped in the valve if a proper bleed procedure is used.


I don't remember if I asked,... As a last step in the bleed process, are you bleeding the lines at the master? Air will definitely get trapped there no matter how much you bleed at the wheels. Simply crack the lines open, giving the nut about a 1/4 turn, have someone press the pedal slowly to the floor an hold, then snug the line, pedal up, 15 count, then repeat at least once or until no more air is coming out. You will know it if there is air; it will sputter as it squirts out.

 

[Ecomike]

Update time on my soft brake peddle nightmare !!!1
Finally broke down and replaced the driver's side caliper and brake hose. Had no real reason to suspect them, but they are the oldest parts (maybe 3 years old?), on the 87 jeep.

Got the wrong caliper and lost all brake action ( I know what lots of air in one caliper feels like now, ZERO brakes, peddle goes to the floor like nothing...). Turns out there is a front mount and rear mount caliper for our jeeps (A detail I screwed up on at the parts counter), but they can both be installed on a rear mount like mine, but putting a front mount on the rear leaves the bleeder screw at the bottom and not the top, so the air gets trapped no matter how hard or well you bleed the sucker..

So for others here with a spongy peddle/poor brakes, be sure the bleeder screw is mounted on the top side of both calipers!!!

Not sure which jeeps got front versus rear mount calipers? Anybody know?


Got the correct new caliper and new hose and still have a spongy brake peddle, but the brake action is a wee bit better, than last weeks small improvements.

Now for a curious note. When we installed the wrong caliper we clamped off the new hose to test that section (driver's side hose and caliper) since I had lost all signs of working brakes (before I figured out it was the wrong caliper), and guess what????

I had a hard peddle with the engine on, like when I first tested the passenger side weeks ago that made me change the caliper and hose on that side (rotors were both already new) because the test said the newish hose or caliper was bad.

So I have now seen two times where I isolated a bad part (passenger side) or trapped air (drivers side) that confirmed the MC must be good.

UNLESS!!!! Clamping off the rubber brake hose at a caliper is affecting a defective area of the MC????

Changing the Passenger side hose and caliper should have solved the mushy peddle problem based on the hose clamp test unless the brand new AZ brake hoses are bad???? But the prior ones were only 3-4 years old and where Rock auto sourced Bendix hoses.

Oh, and we have little trouble bleeding any of the brake lines lately after replacing a part...

The new one man bleeder set up and new bleeder hoses etc helped. So did getting rid of a used (Leaking air in only) and later a new defective wheel cylinder during this ordeal.

 

[Ecomike]

I've never needed to. I don't think air can get trapped in the valve if a proper bleed procedure is used.


I don't remember if I asked,... As a last step in the bleed process, are you bleeding the lines at the master? Air will definitely get trapped there no matter how much you bleed at the wheels. Simply crack the lines open, giving the nut about a 1/4 turn, have someone press the pedal slowly to the floor an hold, then snug the line, pedal up, 15 count, then repeat at least once or until no more air is coming out. You will know it if there is air; it will sputter as it squirts out.

NO. I have never done that. That may indeed be the magic bullet I am missing. THANKS!!!

I had always wondered how the last bit of air could get out of that area since air rises and brake fluid falls.

Since you are such an expert, what is you opinion of the so called need to bench bleed an MC. I just read on Pirates site that he only uses 75% of the stroke length to bench bleed? About 1" out of 1.5" of stroke length.... My old mentor friend of mine said to always use the full stroke and always bench bleed to get air out of the end of the MC? I must have done 30 MCs in 43 years and until this problem, I almost never bench bleed the MC, with no problems as a result.

I always did a sort of bench bleed while mounted on the vehicle before connecting the lines to the MC.

 

[Ecomike]

I've never needed to. I don't think air can get trapped in the valve if a proper bleed procedure is used.


I don't remember if I asked,... As a last step in the bleed process, are you bleeding the lines at the master? Air will definitely get trapped there no matter how much you bleed at the wheels. Simply crack the lines open, giving the nut about a 1/4 turn, have someone press the pedal slowly to the floor an hold, then snug the line, pedal up, 15 count, then repeat at least once or until no more air is coming out. You will know it if there is air; it will sputter as it squirts out.

Thanks!! I will give this a try tomorrow!!

 

[Digger87xj]

If the bleeder is on the bottom them you have the caliper on the wrong side.

I always bench bleed. Always.

 

[Digger87xj]

The length of the stroke to bleed the master depends on the method used. When using tubes to recycle the fluid back into the reservoir, then 100% stroke.
If using block off plugs then short strokes are used until no bubbles rise from the ports.

 

[Ecomike]

I've never needed to. I don't think air can get trapped in the valve if a proper bleed procedure is used.


I don't remember if I asked,... As a last step in the bleed process, are you bleeding the lines at the master? Air will definitely get trapped there no matter how much you bleed at the wheels. Simply crack the lines open, giving the nut about a 1/4 turn, have someone press the pedal slowly to the floor an hold, then snug the line, pedal up, 15 count, then repeat at least once or until no more air is coming out. You will know it if there is air; it will sputter as it squirts out.

Thanks, we did this today and bleed all four wheels again. May have gotten a tiny bubble or two at each point .... we had driven already driven it which may have dislodge the last bubble or two and migrated it to the bleed screw area?).

No change in the soft peddle.

What puzzles me is that twice I clamped off a single brake hose on the front side, a disk caliper hose, once on the passenger side, and once on the drivers side weeks later, and on those two occasions I got a hard pedal with very little pedal movement, like normal brakes. So I replaced the hose, rotor and caliper on the bad side after each test (both sides now), and it made no difference either time or side. Clamping off the hose to the rears made no difference indicating the rears were not the problem. And the front hose test indicated the rears were not a problem.

So I concluded the vac booster and MC and rear brakes must be good, and that the combo valve was also OK and not the problem based on the clamped off hose tests. But not sure why the passenger side hose clamping said the drivers side was OK one day, and then after replacing the passenger side hardware, no change and weeks later a hose clamp test on the drivers side said the drivers side was the only problem???

What the hell am I missing????

I get solid brakes but with a mushy pedal and it takes 3 inches of pedal travel to get good brake action.

 

[Digger87xj]

I got nothing.

 

[yossarian19]

I lost track.
Are the rear drums adjusted tight?
Stock brakes all around?

 

[Ecomike]

I lost track.
Are the rear drums adjusted tight?
Stock brakes all around?

Yes and yes. The key data IMHO is the clamped off rubber brake hose tests. Every thing except the Combo valve is new. No problems bleeding. Have brakes after 3" of mush.

 

[XJ-ARNIE]

I read this entire thread this morning, if your rear brakes are adjusted properly, and installed correctly, the only culprit is air in the system.

Based on what I've read, I would imagaine that the rear brakes are adjusted correctly, and installed correctly.

So, my professional opinion (with out my own eyes on it, and my own tools turning the bolts in my own shop, on my own rack) I'm going to draw the conclusion that you have air in the system. This air is located in the rear, and the only way it's coming out is by using the special tool to bleed the proportioning/metering valve. (technically called a combination valve) It's job is to delay fluid flow to the rear so the drums don't lock up instantly, and then meter the pressure during braking with waaayyy less to the drums, if it wasn't there, the drums would just self energize and lock up at every light.

All of that being said, there is a special tool to bleed that bastard, and I'm pretty sure it will solve your dillema. I've got a few different style in box at my facility, and I do not need them to often, but I have solved this issue on jeeps, trucks, SUVs, cars, station wagons, vans, anything with a disk front, drum rear with one if the aforementioned tools on many occasions.

WWW.tooltopia.com

Www.thetoolwarehouse.net

You can find the one you need at one of these vendors. If you were in Illinois by me (where brake lines rust, and brake repair about covers my overhead every month) Id tell you to stop by, and we'd get her done together. Let me know If i can help.