Master cylinder replacement and brake bleeding hasn't fixed a soft brake pedal

[JayOh]

I bought a 2011 JK sport a few weeks ago and during the test drive I noticed the brake pedal was very soft. I bought it anyway hoping a fluid replacement would fix the pedal, but no luck. My mechanic noticed the master cylinder was leaking so we tried to source a replacement. Due to parts shortage we tried two different parts from a wrecker and no amount of manual bleeding, pressure bleeding or computer bleeding has improved the pedal.

I ended up buying a new genuine Mopar Bosch unit from Rock Auto which arrived this week, but still the same problem - no amount of bleeding will fix the soft pedal.

I've read on other forums that the ABS may need bleeding which requires a scan tool. I'm not sure if the 'computer' bleeding the mechanic mentioned is the same as a scan tool bleed, but I will check with him.

Outside of that are there any other suggestions?

Thanks in advance!

[RLT]

Is the brake peddle soft when engine is on. or just slowly depresses with constant pressure when off ?
If its the latter I believe its quite common.
My 2007 built 2.8CRD has been like that since new.

[JayOh]

When the engine is on

[RLT]

Originally Posted by JayOh

When the engine is on

Probably need to do ABS bleed.
I've read that brake fluid can leak into the servo, but if you've got no drop in level from your new master cyl. wont be that.
But there's members on here with much more knowledge than me !

Just had a guy with exactly the same issue with his 2009 2.8CRD Cherokee over here in England, which I believe has the same brake system as the Wrangler and followed the same path as yourself re Master cylinder and even purchased a used ABS unit which made no difference.
He purchased a 2020 Autel Maxicheck Pro off Amazon to bleed the ABS.
Apparently he's now back on the road, but didn't give any further detail to what he did.
Here's the link to the post on Jeep Owners Club forum
https://community.jeepowners.club/to...e-2009-brakes/

Good Luck in getting it sorted

[JayOh]

Thanks for that link, interesting reading. I'll pass it on to the mechanic and see if he has done an abs bleed.

[JayOh]

This is getting frustrating, I've got a lift kit and a new set of tyres ready to fit but the mechanic can't get these brakes to work. So far he has:

Done a bench bleed on a brand new, genuine Mopar master cylinder.
ABS bleed with his scan tool
Manual and vacuum bleed of all wheels
Check caliper alignment ensuring nipples were on top
Clamped off all four brake lines at the caliper and tested the brake pedal with no change, so the problem is not likely at the caliper end.

Next step is he is trying to source some screws to blank off the ABS to try and isolate the fault further.

Is it possible there could be an air leak in the ABS module?

Anything else to try?

Thanks!

[Fishframe]

Seems not uncommon on JK’s. This is an interesting read - https://www.jk-forum.com/forums/modi...lation-278094/