Brake Booster Fail

[CrazyTrainJK]

Today started with me replacing my rotors and brake pads, front and rear. The pads required a break in and when I went to do the hard braking the first time was a little spongy but squalled the tires. The next 4 times I could push the pedal to the floor. I did not do anything with the calipers today either.
I started checking for leaks. None
I removed the vacuum line from the booster and plugged it and then tried the brakes. Hard pedal and good brakes. So that leaves me with a defective booster??
Am I missing something? Has anyone heard of this or has the same issue?

thanks

 

[WJCO]

Booster shouldn't be related to pad and rotor replacement. Also, typically when a booster fails, the brakes will be very hard and it's much more difficult to slow down the vehicle.

 

[MericaMade]

If it is a booster I have that and MC sitting in garage. Will ship to you if want, just cover shipping and its your. Out of a 17 with 26k miles on it.

 

[CrazyTrainJK]

Well, Wasn't the booster I am at a loss! I even bled the brakes just to be sure and no difference. The pedal will just slowly go to the floor with the motor running. I hate to keep spending money just replacing parts. Any help ?

 

[WJCO]

Well, Wasn't the booster I am at a loss! I even bled the brakes just to be sure and no difference. The pedal will just slowly go to the floor with the motor running. I hate to keep spending money just replacing parts. Any help ?

When you put the new pads on and collapsed the caliper pistons, did you open the system or not? If you pushed the old fluid through the master cylinder, you may have damaged it. The symptom you are describing is either air in the system, a bad master cylinder, or a bad abs modulator (hydraulic).

 

[jesse3638]

When you put the new pads on and collapsed the caliper pistons, did you open the system or not? If you pushed the old fluid through the master cylinder, you may have damaged it. The symptom you are describing is either air in the system, a bad master cylinder, or a bad abs modulator (hydraulic).

What would be the correct way to do this? When I installed my BBK I collapsed the calipers as I've done for years (removed the pads and carefully with a C-clamp). Should I have opened the bleeder before collapsing them and allowed fluid to flow out? I did experience what the OP is describing but after driving and some pumping the breaks returned to normal feeling.

 

[WJCO]

What would be the correct way to do this? When I installed my BBK I collapsed the calipers as I've done for years (removed the pads and carefully with a C-clamp). Should I have opened the bleeder before collapsing them and allowed fluid to flow out? I did experience what the OP is describing but after driving and some pumping the breaks returned to normal feeling.

You should open the bleeder when you collapse the caliper piston so the dirty brake fluid doesn't push upstream in the system. I've personally damaged parts in the past by not doing it this way.

 

[jesse3638]

You should open the bleeder when you collapse the caliper piston so the dirty brake fluid doesn't push upstream in the system. I've personally damaged parts in the past by not doing it this way.

Good to know. Also if one was to do a break fluid exchange without the shop equipment what would be the best way to do that?

 

[WJCO]

Good to know. Also if one was to do a break fluid exchange without the shop equipment what would be the best way to do that?

It's time-consuming, but start with the RR wheel, open that bleeder and let it drain while keeping the master cylinder full. When the fluid coming out of the RR is clean, then close it, move to the LR wheel and do the same thing. Then RF, and last LF. During the entire process, make sure the brake fluid reservoir stays full. It's basically gravity. If you leave the brake fluid cap off, it goes quicker.

 

[jesse3638]

It's time-consuming, but start with the RR wheel, open that bleeder and let it drain while keeping the master cylinder full. When the fluid coming out of the RR is clean, then close it, move to the LR wheel and do the same thing. Then RF, and last LF. During the entire process, make sure the brake fluid reservoir stays full. It's basically gravity. If you leave the brake fluid cap off, it goes quicker.

OK that's what I was thinking. Drip drip drip for hours...haha. I can't bring myself to pay a shop or the dealer to do it when I can get a quart of DOT3 for under $10. Sounds like a good project to clean up the garage, listen to music and drink beer while waiting...haha

 

[CrazyTrainJK]

When you put the new pads on and collapsed the caliper pistons, did you open the system or not? If you pushed the old fluid through the master cylinder, you may have damaged it. The symptom you are describing is either air in the system, a bad master cylinder, or a bad abs modulator (hydraulic).

Yeah, talked to local shop and we are all in agreement the seals in the master cylinder set are bad so I guess Monday I will order a new master cylinder

 

[jeeeep]

my 2010 felt like what you've described. I had to engage the ABS then immediately do a break bleed.
If you have a stretch of road with little traffic, you can slam the brakes enough to kick the ABS on then immediately bleed the brakes - start with farthest.
have someone with you to pump the brake
have the tools you need and enough fluid cause you'll need to do it at least 3 times

 

[Yavapai]

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.

 

[jeeeep]

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.

was the issue resolved after the 3rd master cylinder? did they find brake fluid in the booster? brake fluid can't magically disappear, it always leaves a trail
I would argue the JK master cylinder is enough to handle the stopping job but must be bled correctly to get that firm brake pedal back.
I first used the Powerstop kit when I ran 35's and towed a 5x8 trailer, for even better stopping power, the Dynatrac ProGrip brake kit solves that issue and I'd say a must with 37's.

 

[CrazyTrainJK]

was the issue resolved after the 3rd master cylinder? did they find brake fluid in the booster? brake fluid can't magically disappear, it always leaves a trail
I would argue the JK master cylinder is enough to handle the stopping job but must be bled correctly to get that firm brake pedal back.
I first used the Powerstop kit when I ran 35's and towed a 5x8 trailer, for even better stopping power, the Dynatrac ProGrip brake kit solves that issue and I'd say a must with 37's.

I am installing the master cylinder today. Hoping all goes well. Unfortunately right now I don't have enough brake pedal to engage the ABS. I will update later today.

 

[CrazyTrainJK]

Master cylinder did not fix the problem So new booster and master cylinder along with bleeding the brakes what’s seems like 50 times and still have spongy pedal to the floor??????

 

[CrazyTrainJK]

When you put the new pads on and collapsed the caliper pistons, did you open the system or not? If you pushed the old fluid through the master cylinder, you may have damaged it. The symptom you are describing is either air in the system, a bad master cylinder, or a bad abs modulator (hydraulic).

WJCO, is there a way to test if the abs modulator is bad? Isn’t the abs system covered under warranty?

 

[WJCO]

WJCO, is there a way to test if the abs modulator is bad? Isn’t the abs system covered under warranty?

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?

 

[CrazyTrainJK]

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?

Yes, I bench bled the master cylinder and bled the brakes several times with a clear hose hooked up and no bubbles.

 

[WJCO]

Yes, I bench bled the master cylinder and bled the brakes several times with a clear hose hooked up and no bubbles.

And while having someone push on the brake pedal, no bubbles around the threads of the bleeders on each caliper and no bubbles on the banjo bolts where the hoses bolt up?