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

[Fishframe]

Jeep JK $17,500
Mechanics to sort out brake diagnosis $800
Jeep Dealer to look at brakes at over inflated hourly rate $10,000
More mechanics to actually fix brake problem with new parts $1,000
Uber costs in interim while car unusable $250
New iPhone after throwing the other one in frustration $1,200
Finally get Jeep back and discover rocker cover leaking oil $500

It’s true, “Just Empty Every Pocket”

[JayOh]

The tally so far:

Local mechanic: diagnose leaky master cylinder, can't find a new replacement so tracks down a used one, bleeds it up and fits it, no improvement. Arranges replacement from supplier, bleeds it up and fits, no improvement. I arrange a new genuine part from US - he bleeds it up and fits it, no improvement. Carries out ABS bleed, no improvement. Removes master cylinder to test and bench bleed again. No improvement. Don't know how many hours spent or how much brake fluid he has gone through in all of this, total charge - $0.

Jeep dealer - don't have the bill yet but expecting around $500 for a couple of hours labour and a couple of bottles of brake fluid to bleed brakes and ABS with no improvement.

Their next step is to remove the booster to check and test - quote over $1,000 in labour plus parts, no guarantee it will fix.

If it's not the booster the next step is to check a hose near the brake booster... I can only imagine this is the vacuum hose they're talking about?

Nothing further is going to happen before the new year so I'll be picking it up from the dealer later, no further ahead and a few hundy $$ poorer...

[Classic Boy]

I would be systematic, given what has been tried. I would go to pick a part wrecker and cut out some short brake pipes with the threaded union nut, and crimp the open ends ends and if you have access to to hearing torch seal the crimp. I would fit them to the master cylinder ports as blanking plugs and see if the pedal can be bled to satisfactory hardness. If a satisfactory pedal can be achieved then move the plugs to the outlet ports of the abs module and then see if a hard pedal can be achieved. If ok then go to the wheels.

[Hayesio]

Gees, sounds like a challenging issue but surely it can't be that hard. You need to try and collect more symptoms linked to the problem - like a detective solving a crime - something is definitely not right there and there will be other symptoms. The first thing I would look for is any leaking - master cylinder, caliper cylinders, lines, connections etc. Do the brakes all actuate evenly? Is there any pull to one side or a feel of uneven braking? Take the jeep onto a gravel road and brake heavily, is there any lock-up? You can also test the ABS on a gravel road. Disconnect the brake booster and drive around, is the fading still there? Alternatively, take it to the top of a hill and roll down with the engine off (but key turned to ON!) - this effectively removes the booster from the equation. Does the reservoir drop when the brakes a depressed but slowly return to level? Also, rubber brake lines are known to deteriorate and cause "sponginess" as they expand under pressure, maybe check that out too.

[Fishframe]

Maybe the brake pedal is fine and you have in fact got a ‘spongy’ leg?

[alexbrown64]

It’s always something that’s overlooked.
On my XJ, I had the spongy pedal and I did Everything!!
Ended up being the rails that the front pads sit on. They get grooved and the pads would hang and twist in the grooves. They couldn’t slide evenly. This caused high and low spots in the pads and required a lot more pedal travel. Once I welded the grooves, Installed new pads and checked for smooth operation, I had a high and perfectly operating pedal again. I spent months chasing this problem, including bleeding and replacing ABS modules etc...

My point is....remove wheels, check rotors and pads for wear/uneven wear, and replace. New pads and checking all the components that they work around can make a big difference to pedal travel. That’s front and rear.

Cheers,

[JayOh]

Just picked it up from the dealer, the bill for the bleed was $300 for parts and labour. They made a comment that the master cylinder did not appear to be genuine which is a bit of a surprise as I'd ordered the genuine Mopar part from Rock Auto which arrived in a genuine Mopar parts box...

I'm assuming Rock Auto is a reliable source for genuine parts?

Still no closer to sorting the issue out though, next step will probably be a trip to ATV in the new year and hopefully they will be able to sort it out. In the meantime the christmas off-roading plans are on hold.. probably much like a lot of other people's holiday plans.