I was driving around today and noticed that every time I try to brake while going over some bumps, the brake pedal seems to go soft and the car stops braking until I am on a smooth surface again. The pedal also seems to vibrate when this is happening. I went to a side street and tested the brakes a few times going about 10 MPH and slamming on the brakes to see if it would happen and sure enough it did the same thing but every once in a while.

Has anyone else experienced this or can tell me as to what the problem may be?

I appreciate your help!

 

My guess is that your ABS is kicking in.

 

Unless it is pulsing, I'm not sure about the ABS but I noticed it a couple times but it was when I was going over a speedbump a little fast like when the Jeep lifted a bit but very rare. I guess that could be an ABS thing or some way our ESP or other nanny controls activate. If it's happening during normal braking, that's not right and you should have it checked.

 

It seems like the ABS is working properly. Throw in a little ESP and everything is playing at once. I make it a point not to directly brake going over bumps in the road; either before and coast over them, or after. Your ABS is kicking in once in awhile on a level road because it's not slippery enough to kick in every time you brake hard. Since you have an 07, when was the last time your brakes were checked. If they're original you probably need rears at the very least. Yes, rears go first on these. The only part I don't like is the peddle seeming to go soft. At this point, due to age, mileage, etc., I would have them checked. Check your brake fluid also. If it's a bit low that could mean your pads are low.

 

Thanks for the advice fellas....I am going to get everything checked soon to see what is going on.

 

There has been a rash of what you are describing in my area lately... 'Mushy brake pedal' One of the local off road shops has six (mainly 2007-2008) JKs with the same problem. They also shared that one customers power brakes failed completely as a result. I recently had them do a lift and install braided lines and now I have the same problem. I have never been a big fan of the JK brakes and initially thought it was just air in the system (have bleed twice) or the physics of the larger tires (but it happened at very low speeds as well, like when parking) it was kinda scary sometimes, like WHOA Nellie! I also get a little pop sound sometimes after taking my foot off the pedal, as if the pedal is popping back up. Right now the assertion is that the 2007-2008 brake master cylinder is a piece of meat. The best answer they have come up with so far is to possibly replace the stock master cylinder with one from the Chrysler military JK (known as the J-8, link: http://www.jeep-j8.com). This is the same master cylinder that Teraflex is advising customers to upgrade to when they opt for their 'big brake kit'. Chyrsler SHOULD be looking into this...

Teraflex Big Brake Kit
http://www.teraflex.biz/jk-big-brake-kit.html

Larger Bore Master Cylinder in question…
http://www.teraflex.biz/brake-master...ized-bore.html

I will post more when I find out how the bigger bore cylinder works out on another Jeep.

 

I have noticed the same thing with my 08' Unlimited. The brakes seem to work fine on the road, but when you come to a rest at a stop light or in a parking lot with the engine running, you can press firmly on the brake pedal and it will go all the way to the floor.

This is a tell tale sign of a leak (can't build pressure), air in system (air compresses when you hold pressure on the pedal) or a bad master cylinder (allows fluid past the seals).

However, at only 58,000 miles and bone stock it is hard to believe any of these problems have occurred. A leak would be possible, but I don't see any. Are you guys saying that it is common for the master cylinder to fail this early in life on these Jeeps?

If the MC is bad, that is something that needs to be replaced as you are not getting full, sustained braking force and that could make a difference in a panic stop.

 

Well,

I finally got back to post... One of the local 4x4 shops talked me into replacing the master cylinder to address the 'soft pedal' issue. They made me a deal I couldn't refuse The changout is also recommended by Teraflex when installing their "JK big brake kit" (calipers, rotors). The cylinder is a Chrysler part used on the military export version of the JK (maybe 2009-2011 JKs as well?). The outside appearance is just about identical with supposedly a 14% larger bore. It has a part number of CHR-68045998AB(?) I believe. After driving it for a couple weeks (all of it on road) I have to say it is an improvement over the 'soft pedal' I had before. Braking does seem a little firmer, but then again, I did not like the original configuration at all. I have even been doing some light towing (about #1000) and it seems good to go. I believe the wholesale price on the part is about $90 (Teraflex MSRP $199, Part# 4303450 ) and not sure how much the labor would normally be if you don't do it yourself. For the price of just parts I think it worthwhile, especially if you are upgrading calipers and rotors, but don't know if I would drop a couple hundred to include having someone install it. It did cure the whole soft pedal issue though.

I have also seen some references regarding the soft pedal being due to trapped air in the system from not properly bleeding the braking system. Traditional bleeding does not always work ,as air can be trapped in the ABS portion of the system. The dealer procedure calls for bleeding then hooking it up to their equipment to cycle the ABS valving to release any air then re-bleeding.

Cheers

 

I am having some of the same problems with my jk as well. I think it is time I upgraded. thanks for the knowledge.

 

It seems like there are multiple different symptoms being described with different fixes.

I had a similar problem as the OP described. It was due to a bad ABS wheel speed sensor. You might want to read this topic that I started for further information to see if it sounds similar to what you're observing. The brake pedal going all the way down to the floor intermittently is definite.y different than the brakes intermittently slipping. Pedal travel is typically always related to some type of brake fluid problem be it air bubbles, Master Cylinder, Caliper problems, etc.)

https://www.jk-forum.com/forums/stoc...gnosis-331956/

Here's my symptoms from that thread.