Brake Booster Fail

WJCO said:
That sucks that it didn't fix it. Did you bench bleed the master cylinder first?

Some manufacturers have a way to isolate each part of the ABS hydraulic circuit of the HCU with a scan tool. I've tested them manually by plugging various parts of the brake system so you can find where the hydraulic pressure loss is but it's a time-consuming process. Along with that, it's such a rare failure that I haven't done it often. It should be covered under regular factory warranty if you're within the time and mileage. And you're 100% sure there's no fluid bubbling slightly at all bleeders and hose connections?
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Took it in to my local dealer and they put the laptop on it. No codes or anything so we scheduled it for an ABS bleed next Friday. They seem to think that will fix it.
 
WJCO said:
That sounds like a logical next step.
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Well, local Jeep shop did an ABS bleed and no change. They said the back calipers were bad. So on their advice I changed the rear calipers and again no change🤬🤬🤬

so here is my question? I replaced my rubber brake lines with the EVO steel braided ones when I initially did the lift back in 2016 or 2017. Could one of those hoses be bad?
I am grasping at straws because I am out of ideas
 
Are they extra long? Is there a high point in which creates a loop / arch? Since we’re grasping at straws here if there’s an arch in the line a bubble can stay in it even while bleeding. Would need to remove caliper and straighten line to the lowest point you can and then bleed.
Yavapai said:
I have had a similar problem with my 2015 Rubicon JKU with 35" tires. Spongy Brakes. I I have bled them several times. Replaced the front pads, and have replaced master cylinders 3 times and still have spongy brakes. I was told by someone that the problem is the larger tires and the stock master cylinder that simply cannot handle it. Also, bake fluid would magically disappear which is why we changed master cylinders. My 4WD shop told me they thought it was going through the vacuum booster and vaporizing into the engine.
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Tires don’t cause a spongy pedal. Pedal dropping to the floor with little pressure has not a single thing to do with tires.


Are the extended lines extra long? Is there a high point in which creates a loop / arch? Since we’re grasping at straws here if there’s an arch in the line a bubble can stay in it even while bleeding. Would need to remove carpet straighten to the lowest point you can and then bleed.

When did you first notice the spongeyness. And to be clear the feel is a system with air in it, a pedal with little resistance, correct? Not just shitty braking performance. Have you had someone step on the pedal while you inspect any rubber lines for bulging?
 
Snboarder113 said:
Are they extra long? Is there a high point in which creates a loop / arch? Since we’re grasping at straws here if there’s an arch in the line a bubble can stay in it even while bleeding. Would need to remove caliper and straighten line to the lowest point you can and then bleed.

Tires don’t cause a spongy pedal. Pedal dropping to the floor with little pressure has not a single thing to do with tires.


Are the extended lines extra long? Is there a high point in which creates a loop / arch? Since we’re grasping at straws here if there’s an arch in the line a bubble can stay in it even while bleeding. Would need to remove carpet straighten to the lowest point you can and then bleed.

When did you first notice the spongeyness. And to be clear the feel is a system with air in it, a pedal with little resistance, correct? Not just shitty braking performance. Have you had someone step on the pedal while you inspect any rubber lines for bulging?
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The pedal feels normal under typical braking but when you push hard on the pedal it will go to the floor when the engine is running. When the engine is off the pedal only moves a couple 3-4 inches. I am on a time crunch for our trip to Moab so I just ordered new braided brake lines hoping that will take care of it. I have thrown everything else at it LOL.
 
CrazyTrainJK said:
Well, local Jeep shop did an ABS bleed and no change. They said the back calipers were bad. So on their advice I changed the rear calipers and again no change🤬🤬🤬

so here is my question? I replaced my rubber brake lines with the EVO steel braided ones when I initially did the lift back in 2016 or 2017. Could one of those hoses be bad?
I am grasping at straws because I am out of ideas
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even though you've done the bleed and it appears there is no air, the ABS must have some cavity that traps air but you won't notice it until you apply the brakes.
Here's what I did when I bled my JKU brakes wrong and introduced air into the system -btw, I could hear a buzzing sound when they were really spongy, to the floor spongy but given enough distance they were stopping me. I did a brake pump bleed to stop the buzzing but still had spongy brakes.
I bought a Motive Power Bleeder 0103, this allowed me to pressure test per the instructions (no fluid in the power bleeder) to make sure that the master, booster, calipers/bleed screws were all good. Do not over pressurize the system, you will cause damage.
Once I confirmed pressure was holding, I bled the brakes again per the instruction using the pressure of the power bleeder only - no brake pedal pumping.
Keep an eye on the fluid, and pressure of the motive. you want to keep it filled and with steady pressure that allows the fluid to flow properly.
I was surprised at the amount of air that was in the system.
After this the brakes felt a lot better but still not 100%, that's when I took everything and did an ABS bleed.
I've since bought a cheap unit that allows me to trigger the ABS so I can bleed in my driveway - haven't used since I tested it but it was a lot easier to do a brake bleed with the Motive and the ABS unit in the driveway than the slamming on the brakes method and brake bleeding off the side of the road.
Edit:
For anyone else doing a brake swap, don't push the caliper piston in without opening the bleed valve, pushing the fluid back up thru introduces air into the system. I've done it for years not wanting to "waste" fluid but I was informed that ABS are different and that's how I introduced air into the system.
I've since changed brake pads on my 2010 and 2015 JKU, add some fluid, opened the bleed screw to push the caliper back and no spongy brakes.
If I added too much fluid, I do a gravity bleed - no brake pedal pumping.
 
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Well,
I had a few friends in our Jeep club try their brake pedal and they have the same result. If you hit the brakes they will stop you but If you continue to press hard on the pedal after you stop it will continue down. I ordered and installed the Crown Big Brake Kit on the front and replaced the braided lines and purchased and used a pressure bleeder to bleed the system and I have a good pedal. Of course if you press hard after you stop you can still press the pedal down but the Jeep stops better than it has in years.
 
I am experiencing the same issue. I thought it was a fluid problem. I've flushed the whole system, pedal is still sinking.

my issue is air is in the ABS unit. I cracked the lines at the aluminum box and confirmed there IS air in the system. The master cylinder just doesnt have enough throw to burp it out or the air is stuck in the valve body.

I do not own a motive power bleeder and OBDtool capable of triggering the ABS system so I scheduled an ABS Bleed with the dealer for Tuesday this week, I'm going to have them do the airbag recall while it's there... because I still haven't had time to get that taken care of.

...Will report back after the $179 minimum charge.
 
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DWiggles said:
I am experiencing the same issue. I thought it was a fluid problem. I've flushed the whole system, pedal is still sinking.

my issue is air is in the ABS unit. I cracked the lines at the aluminum box and confirmed there IS air in the system. The master cylinder just doesnt have enough throw to burp it out or the air is stuck in the valve body.

I do not own a motive power bleeder and OBDtool capable of triggering the ABS system so I scheduled an ABS Bleed with the dealer for Tuesday this week, I'm going to have them do the airbag recall while it's there... because I still haven't had time to get that taken care of.

...Will report back after the $179 minimum charge.
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You can trigger your own abs bleed while driving. I do it at work in the bigger trucks. I will hit around 40-50mph then slam on the brakes in a grass section just off the road. It will cause the abs pump to activate and bleed to unit. Do that a few times then rebleed the system at each of the calipers
 
cozdude said:
You can trigger your own abs bleed while driving. I do it at work in the bigger trucks. I will hit around 40-50mph then slam on the brakes in a grass section just off the road. It will cause the abs pump to activate and bleed to unit. Do that a few times then rebleed the system at each of the calipers
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Remind me what dealership your at so I can avoid 😳 lol
 
cozdude said:
You can trigger your own abs bleed while driving. I do it at work in the bigger trucks. I will hit around 40-50mph then slam on the brakes in a grass section just off the road. It will cause the abs pump to activate and bleed to unit. Do that a few times then rebleed the system at each of the calipers
Click to expand...
I did this with my JKU, took what I needed to bleed the brakes with me to a dirt road that doesn't get used much and could up to speed. Made sure the reservoir was topped off, got up to about 50 then slammed on the brakes, checked the reservoir level, repeat and bled the brakes, repeat once more.

It was time consuming but got the job done.

I've since bought a cheap OBD scan tool with ABS autobleed.
 
The dealer just called.

To my shock - did the "gravel road to trigger the abs" then bleed. The pedal is still the sinking.
They want $11XX to replace the master cylinder
which they say may be "bypassed" due to a seal failure.

I can 100% confirm there is air trapped in the brake system at the hardlines to the abs unit.

So I'm out $230 for their time?

Looks like yet again I am going to fall back on the old reliable - "if you want it done right, do it yourself"

So these are my current thoughts:

Step 1) get the jeep back from the stealership.

I understand paying for the techs time, but $230 for them to not be able to confirm with confidence that all the air is out of the brake system, not pressure test the master cylinder, and just recommend I "throw money & parts at the problem" is what am I paying for? Has anyone successfully negotiated the technician charges for failure to perform services?

Step 2) I plan on purchasing a motive power bleeder (Unless the community here recommends otherwise)

Step 2a) I will consider purchasing a scantool capable of triggering the ABS pump (Again unless the community here recommends otherwise)

Step 3) I plan to pressure test the master cylinder as a first step check in sanity

Step 4) I plan to pressure bleed the entire system

Step 5) I plan to enjoy my jeep with restored confidence in braking performance and a firm pedal
 
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DWiggles said:
The dealer just called.

To my shock - did the "gravel road to trigger the abs" then bleed. The pedal is still the sinking.
They want $11XX to replace the master cylinder
which they say may be "bypassed" due to a seal failure.

I can 100% confirm there is air trapped in the brake system at the hardlines to the abs unit.

So I'm out $230 for their time?

Looks like yet again I am going to fall back on the old reliable - "if you want it done right, do it yourself"

So these are my current thoughts:

Step 1) get the jeep back from the stealership.

I understand paying for the techs time, but $230 for them to not be able to confirm with confidence that all the air is out of the brake system, not pressure test the master cylinder, and just recommend I "throw money & parts at the problem" is what am I paying for? Has anyone successfully negotiated the technician charges for failure to perform services?

Step 2) I plan on purchasing a motive power bleeder (Unless the community here recommends otherwise)

Step 2a) I will consider purchasing a scantool capable of triggering the ABS pump (Again unless the community here recommends otherwise)

Step 3) I plan to pressure test the master cylinder as a first step check in sanity

Step 4) I plan to pressure bleed the entire system

Step 5) I plan to enjoy my jeep with restored confidence in braking performance and a firm pedal
Click to expand...
hope ABS bleed takes care of it. replacing the master cylinder isn't too much effort and cheaper than paying dealer labor prices.
 
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