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Discussion Starter · #1 ·
I have a 2014 GC diesel with 55000 miles on it. If I get in the car and step on the brake I have a solid peddle but as soon as I fire it up the peddle will slowly sink to the floor when I step on it. Fluid level stays on full. Anyone have any ideas?
 

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2015 WK2 Diesel H.A.
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I just bought a 2015 GC with the Turbo Diesel and Wow it has very good brakes.

This is my first diesel vehicle so I'm not totally up to speed on them but I do know Diesels especially Turbo Diesels don't make vacuum like a gas engine so they must have a vacuum pump to power the brake booster.

I would look into the vacuum pump and the lines from it.
 

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I saw in the parts catalog an electric vacuum pump connected to the Power Booster, I wondered why in the world would you need that? A turbo I could easily see needing one, and probably a turbo diesel even more so. I could be wrong cause I don't know Diesels that well, but I "think" turbo diesels spend more time at positive pressure than gasoline turbos.

OK, my 2011 WK2, I've noticed the Vacuum Check valve on the Brake Booster doesn't seem to hold a vacuum very long. Some cars I've owned will hold vacuum for days, some a day or less. My WK2, I've noticed the booster is out of vacuum within minutes of shutting down the engine.

And that's what I'm getting at. Could you just be mistaking the firm pedal you'll feel because of the loss of vacuum in the brake booster, and when the engine starts and supplies vacuum to the booster, which that now provided boost results in you pushing the pedal to the floor?

How do the brakes feel and perform while driving? Are there any other problems with the brakes other than just what you posted. Cause it could be normal, the only reason it's noticeable on the WK2 is because it brake booster bleeds down vacuum much faster than most cars.

There's another recent thread, stating the same problem and I gave the same advice and the OP replied the brakes work fine while driving, most times he can get the vehicle to stop before the brake pedal hits the floor...... .....Umm, no, that's not normal and you do have a brake problem.
 

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My 13 wk2 brake booster failed found out that they had a major recall on the booster not sure if the 14 diesels fall under that recall
 

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Grand Cherokee
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The recall is for the water shield on the Brake Booster, so unless your brake booster rusted out or rusted internally to cause it to fail, then it likely is NOT related to the recall.

So far my experience with WK2 brakes (I've only had it a couple of months), the brakes seem pretty heavily boosted. The pedal is fairly light and like a heavier pedal.

The Master Cylinder seems unusual, although I don't suspect it's not any different than the basic design, it just doesn't look like your typical MC. And perhaps they don't use the best quality brake fluid as factory fill either.

My 2011 brake fluid was black and full of particulate matter when I got. Bleeding the brakes resulted in the MC having one of its tandem pistons jam at full stroke.

After a new master cylinder it took several bleedings to get all the air out. I suspect air got into the ABS circuits and that was what made bleeding so difficult.

I've only driven 1 WK2, so I don't know how common this is. Perhaps the Brake booster is prone to go bad, and my complaints are booster showing symptoms. Maybe the previous owner did something stupid to have the brake fluid go totally bad and gum up the Master Cylinder.

Regardless, it took more work than I'm used to, but I have good working brakes in my 2011 WK2.

When I had air in the lines, I had the very noticeable drop after starting the motor and the booster getting engine vacuum to provide brake boost. After I got the air out, it didn't drop anymore after starting the engine.
 

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Discussion Starter · #7 ·
Thanks, it's heading for the shop next week. Had a panic stop the other day and my foot could hardly keep up with the peddle.
 

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Brake symptoms are hard to describe, so often I read posts and can't tell if the person has no problem at all, they just don't understand how the brakes work, or they really have a problem and just can't describe it properly.

When I had air in my brake lines, it sounded a lot like you're describing. I know a bad master cylinder can feel like air in the brakes. Heck, unless its a massive leak, a leak feels like air in the brake lines, but you'd be loosing fluid with a leak.

My blown MC, after replacing it, bled and bled, still had air in the lines, pedal felt like what you described. Speculated I might have gotten air in the ABS circuits, especially with all the crazy stuff I was trying to bleed the brakes with the bad MC till I figured out the MC was bad. So I tried to get the ABS to activate on a test drive and then bled the brakes. I got a good pedal and the brakes seemed good for the next week. I activated the ABS while driving, a couple hours later my brake pedal felt like it had a ton of air in them. Bled the brakes again, and the brakes feels even better than before, just about perfect now.

So its always possible you've got air in the ABS circuits, the brake might feel OK, then you activate the ABS for some reason, and the air gets pumped out of the ABS into the lines, and you've got air in the lines and the brake pedal feels just like that.

My pedal feels just short of brand new, so I'm starting to think air in the ABS is the thing, I've gotten just about all of it out. But can't help wondering if there is still a tiny bit left, and the pedal could be even better if I got the last of it out of the ABS.
 

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I've overtightened the banjo bolt on one of the calipers when I did my HD brake upgrade, as well as painting the calipers red. That overcrushed one of the copper washer gaskets and created a brake leak.

So the bad Master Cylinder I can blame on the previous owner. But I did the washer. Its fixed and the rear pads are bedding in now, the brake pedal is starting to feel exactly like it should now.

I had a MC go bad at 70k miles on my WK2. Doing new rotors and pads and bleeding the brakes, destroyed the bad MC (it always does). But continued to have some problems from a brake leak.

BTW, my leak was small enough that I could not notice the brake fluid level going down.
 

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Discussion Starter · #11 ·
Got the master cylinder installed today but now they say they can't bleed the brakes so I was sent home in a loaner.:(
 

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Is this an independent shop or a Dealership? Another thread said an independent shop couldn't bleed the brakes using the ABS Pump, they could only activate the pump for two of the 4 brakes and have to have the vehicle towed to the dealer to do it.

When I replaced my Master Cylinder myself, I bleed it the old fashion way and notice the rear brakes took many times more pumping of the pedal to get the brake fluid flowing out of ther rears.
 

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Discussion Starter · #13 ·
Dealership, they called this afternoon saying they had to order a special tool. Wish they would hurry. My loaner is a Chrysler 300 and I hate it. They couldn't pay me to take one.
 

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Ok, yea I'm getting suspicious of your dealership, they need to order a special tool to bleed the brakes? Hmmm, I replaced my Master Cylinder Myself and bled the brakes and didn't need any special tools.

Do they need to bleed the ABS Pump? That still shouldn't require a special tool, their dealer scan tool should be able to do it.
 

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Lifer: Old Geezer
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I always thought the scan tool was all that was needed also. Not sure what is going on. :(
Your symptom doesn't sound that close to the brake vacuum booster recall, but your location adds it to the list of suspects. Has that been done, and the recall for the recall performed? Plus a vacuum bleeddown test [not part of the recall/recall but many dealers will do it if requested]?

Not to diss your dealer, but a dealer that "has to order a special tool" for a vehicle that has been out since mid-2013 sounds more like they already have a tool--the service manager.
 

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From what I read in the recall, its for a water shield, that if it's installed incorrectly could cause the Power Booster to corrode.

Yes I could see how a corroding power booster could loose vacuum or fail completely, thus a check with vacuum leakdown test. But, I'm skeptical it could cause his symptoms, it would have to be overboosting, and even then, he'd still get corresponding brake force from the brakes for the pedal position. His symptoms sound like the classic failed Master Cylinder.

Something I noticed, you usually don't see rebuilds of aluminum Master Cylinders. The DOT requirements for Aluminum Master Cylinders is to have a special kind of anodizing done cylinder surface wall, this can't be honed or re-andozized practically. Thus impractical to rebuild......

....unless you have a source of Master Cylinders that failed for the seals or other reasons, leaving a still good cylinder wall surface......

.....and on this forum I see multiple posts that have symptoms of a bad master cylinder.....

....My Master Cylinder failed, and it was the seals that inside it that disintrigated....

....when I went to get a new Master Cylinder, I saw rebuilds for this master cylinder are being sold..... ....most cars, that didn't have Master Cylinders fail till they were coming up on 200k miles, you can only find aluminum Master Cylinders that are brand new being sold, no rebuilds....

So I suspect the Master Cylinder, like the Water Pump, typically fail early on the Jeep Grand Cherokee.
 
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