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Unread 04-19-2009, 12:21 AM   #1
Chandler
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Another mushy WJ brake thread

I hate to ask but since it's a potential safety issue I want to make sure I get as much info as possible. I did search all the old discussions.

I have a 2004 WJ and bought in 2005 used. The brakes have been mushy the whole time. I just thought that's how they were. Last summer I changed my front rotors and pads. The mushy brake feeling was worst than before. To the point I thought something was wrong.

Today I changed my rear rotors and pads and added speed bleeders. I bled the system the best I could and purged out the old fluid. The brakes feel firm with power off but as soon as I start the pedal goes to the floor. I still have great stopping power.

Today I was searching for info on adjusting my ebrake and noticed other threads about mushy brakes and now realize this isn't normal.

I haven't noticed any fluid loss or lack of stopping power. I want to diagnose the issue and resolve since my wife drives the WJ back and forth to work. Friday someone rearended her and I don't want that to be her next time.

I want to diagnose the master cylinder and figure out how to test each caliper. If possible any advice would be great.

If I change the master cylinder how do I make sure I don't create air in the ABS system?

How do you bench bleed a master cylinder?

Thanks in advance.

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Unread 04-19-2009, 08:20 AM   #2
micifus
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every chrysler vehicle I have driven I have noticed "mushy brakes" maybe yours is more so then normal. A lot of times I will double pump the brake pedal. Push it in a little let off then push in again, the second push the brakes should be a lot firmer. Maybe this is just nature of the beast.
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Unread 04-19-2009, 08:38 AM   #3
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My brake fluid was really nasty so i spent all day cleaning and bleeding new fluid through. 2 quarts of brake fluid later, the brakes were not as mushy.

The reservoir had gunk in it so I took it off and cleaned it. Now the fluid is bright and clear.

Unless it is pulling when brakes are applied, I wouldn't start chasing a single caliper.

http://autorepair.about.com/od/fixit...ench-bleed.htm

Google much?
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Unread 04-19-2009, 08:41 AM   #4
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old brake fluid that has been opened and sitting on the shelf for a long time will make brakes feel mushy
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Unread 04-19-2009, 09:09 AM   #5
rm2001wj
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I suspect that the pedal never goes to the floor while the WJ is rolling; but it does after you are stopped and if you push hard on the pedal. I believe that is normal and is due to the way ABS is designed on the WJ. When you are stopped, the wheels are not turning, but you are pressing hard on the brake pedal. The ABS thinks the wheels are locked (they are not turning) and tries to reduce the pressure on the brakes pads. The wheels still are turning so more pressure is reduced. The net effect is that the pedal goes down to the floor as the ABS bleeds off the pressure.

Bottom line is that the brakes act normally if you don't push hard on the pedal when your WJ is not rolling.
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Unread 04-19-2009, 09:59 AM   #6
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Quote:
Originally Posted by rm2001wj View Post
I suspect that the pedal never goes to the floor while the WJ is rolling; but it does after you are stopped and if you push hard on the pedal. I believe that is normal and is due to the way ABS is designed on the WJ. When you are stopped, the wheels are not turning, but you are pressing hard on the brake pedal. The ABS thinks the wheels are locked (they are not turning) and tries to reduce the pressure on the brakes pads. The wheels still are turning so more pressure is reduced. The net effect is that the pedal goes down to the floor as the ABS bleeds off the pressure.

Bottom line is that the brakes act normally if you don't push hard on the pedal when your WJ is not rolling.
The ABS computer knows if your Jeep is moving. It won't activate when you're stopped.

Quote:
Originally Posted by micifus View Post
every chrysler vehicle I have driven I have noticed "mushy brakes" maybe yours is more so then normal. A lot of times I will double pump the brake pedal. Push it in a little let off then push in again, the second push the brakes should be a lot firmer. Maybe this is just nature of the beast.
That's an indication that you have air in the system & they need to be bled.
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Unread 04-19-2009, 10:30 AM   #7
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Quote:
Originally Posted by indept View Post
The ABS computer knows if your Jeep is moving. It won't activate when you're stopped.
...........
The only way that the ABS computer "knows" if the Jeep is moving is by getting signals from the wheel speed sensors. If wheels are not turning, there are no signals.

Nothing is wrong with the brakes if they behave as I described above.
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Unread 04-19-2009, 11:56 AM   #8
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Quote:
Originally Posted by baxy View Post
old brake fluid that has been opened and sitting on the shelf for a long time will make brakes feel mushy
Brake fluid Absorbs moisture in the air is the reason why.
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Unread 04-19-2009, 04:29 PM   #9
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Originally Posted by rm2001wj View Post
The only way that the ABS computer "knows" if the Jeep is moving is by getting signals from the wheel speed sensors. If wheels are not turning, there are no signals.

Nothing is wrong with the brakes if they behave as I described above.
Doesn't the ABS computer monitor vehicle speed otherwise the ABS would be pulsing away when you're stopped at a light.
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Unread 04-19-2009, 05:25 PM   #10
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I guess I'll call it good for now. I would like to get a cap for the master cylinder though and do the trick someone mentioned to use a valve stem to pressurize the line and bleed them.
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Unread 04-19-2009, 06:48 PM   #11
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Quote:
Originally Posted by indept View Post
Doesn't the ABS computer monitor vehicle speed otherwise the ABS would be pulsing away when you're stopped at a light.
WJs don't have a vehicle speed sensor. The PCM and ABS computer both use the wheel speed sensor signals. The pulsing is due to the ABS releasing pressure when a wheel stops turning and then applying it again when the wheel starts turning again. Of course, it only does this in response to heavy brake pedal pressure. Light pedal pressure, like that normally applied when the Jeep is stationary, doesn't trigger any particular ABS response.

As I mentioned earlier, it is heavy pedal pressure when not moving that lets the pedal go down near the floor. Pulsing would only occur if the wheels starts to turn as the ABS reduces the pressure on the pads.
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Unread 04-20-2009, 06:35 PM   #12
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I retested mine this morning on the way to work and my pedal is actually much firmer now. I do believe what is being said as my pedal as full stop will still depress. When I'm driving there was a noticeable new firmness when I braked.
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