Soft brake pedal

[Jump3r]

I have a new to me 2005 LJ and the brake pedal feels squishier than I think it should. It sinks quite a bit before any activation and while it does stop it feels like I have to get almost to the floor for that to happen. This all started when I replaced all 4 calipers looking to solve a sticking piston.

* All 4 banjo bolts have new crush washers on both sides and are torqued to spec. No obvious leaks.
* Calipers are definitely on the correct sides (bleeder screws are at the top)
* New pads and rotors were done at the same time as the calipers.
* While bleeding the brakes after the caliper replacement this I let the reservoir run dry. Yes I am that dumb.
* After letting the system run dry I put 2-3 quarts more DOT4 through the system trying to eliminate the squishy pedal
* Assumed I have air in the master cylinder so tried bleeding it on the vehicle by cracking the lines but no dice
* Replaced master cylinder with a new Centric that was thourougly bench bled
* Bled another quart or so of DOT4 through the system after replacing the master cylinder but pedal still feels squishy
* All bleeding is done with the traditional 2-person swift to the floor after cracking the bleeder method and with @mrblaine 's tool in place to hold the safety valve

I'm a bit at a loss at this point. Any suggestions are welcome. Would love to solve the problem while my wife is still speaking to me

 

[mrblaine]

I have a new to me 2005 LJ and the brake pedal feels squishier than I think it should. It sinks quite a bit before any activation and while it does stop it feels like I have to get almost to the floor for that to happen. This all started when I replaced all 4 calipers looking to solve a sticking piston.

* All 4 banjo bolts have new crush washers on both sides and are torqued to spec. No obvious leaks.
* Calipers are definitely on the correct sides (bleeder screws are at the top)
* New pads and rotors were done at the same time as the calipers.
* While bleeding the brakes after the caliper replacement this I let the reservoir run dry. Yes I am that dumb.
* After letting the system run dry I put 2-3 quarts more DOT4 through the system trying to eliminate the squishy pedal
* Assumed I have air in the master cylinder so tried bleeding it on the vehicle by cracking the lines but no dice
* Replaced master cylinder with a new Centric that was thourougly bench bled
* Bled another quart or so of DOT4 through the system after replacing the master cylinder but pedal still feels squishy
* All bleeding is done with the traditional 2-person swift to the floor after cracking the bleeder method and with @mrblaine 's tool in place to hold the safety valve

I'm a bit at a loss at this point. Any suggestions are welcome. Would love to solve the problem while my wife is still speaking to me

There is no "thoroughly" when it comes to bench bleeding a master. It is either bled or it isn't. If you used OTHER than the plugged port method to bleed it, then you don't know if it was bled or you just bled at it. That and there was no reason to swap it out. Bench bleed the old one and put it back on. Use the plugged port method this time.

 

[Jump3r]

I bench bled the master cylinder using the Dorman kit with the lines running back into the reservoir until i saw no air at all in the lines when i push the piston. I will try the plugged port method.

 

[Jump3r]

Well I bench bled the master cylinder using the plugged port method. Got it to where it had no travel other than the 1/8” or so.

I put it back on the Jeep and bled the brakes again. Still feels very soft (goes almost to the floor) when the engine is started, but quite firm (almost no travel) when the engine is off.

I can try repeating the bench bleed to see if I get different results but assuming I did it correctly any ideas of where I should be looking next?

 

[mrblaine]

Well I bench bled the master cylinder using the plugged port method. Got it to where it had no travel other than the 1/8” or so.

I put it back on the Jeep and bled the brakes again. Still feels very soft (goes almost to the floor) when the engine is started, but quite firm (almost no travel) when the engine is off.

I can try repeating the bench bleed to see if I get different results but assuming I did it correctly any ideas of where I should be looking next?

If it goes to the floor when the engine is started, that is the #1 symptom of an upside down caliper. I know you said you checked, check again.

 

[Jump3r]

I verified that all of the calipers are in the correct orientation.

I noticed something new today. During the bleeding process there is a *very* faint and short whistling sound. It's incredibly soft and I think my wife acknowledging the "push" instruction was masking it before.

The whistle only happens if any bleeder screw is open (front or rear). If I close all of the bleeder screws the whistle goes away. Having a hell of a time localizing it without getting brake fluid everywhere but it seems like it's coming from the front half of the vehicle, possibly in the area of the master cylinder / brake booster. It's so quiet that I can't quite pin it down. My wife had to leave to start doing the after-school ride service thing for a bit so I lost my brake-pushing helper but wondering if anyone has any ideas I can chase down.