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Unread 07-05-2015, 11:12 AM   #1
JWMan
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Brake pedal intermittently goes to floor

Hi,

By any chance any one of you had come across with brake pedal going to the floor every now and then.
My Jeep Wrangler is 2009. Done only 70000Kms. In general, I keep up-to-date services. Jeep is in very good condition. I donít do off road drives.
Couple of months ago I started feeling that suddenly brake pedal hitting almost the floor, but brake applies. Iíve taken it to a local garage and tested and suggested to replace the Master Cylinder Pump. They replaced the pump with new one; made by Mopar. Couple of days later again I felt itís going to the floor.

I went back to the garage and they did a complete bleed out on all four wheels individually. Checked all over and no leaks were found. They checked the brake pads. Brake pads are about 40K Kms done.

On my way back from the garage it happened again; just once. Then I guess after 2 days it happened again and now keep happening at least once every two days or even every day.
I guess there is nothing else to replace.

Has anyone come across such a problem before? Any suggestions?

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Unread 07-05-2015, 02:21 PM   #2
rich6700
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Replace the master cylinder
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Unread 07-05-2015, 04:53 PM   #3
RockyClymer
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Master cylinder.
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Unread 07-06-2015, 07:12 AM   #4
Neo1130
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Master cylinder or air in the brake lines... I just replaced brake lines on a buddies Jeep a couple weeks ago because there was a split in the hard line that acted like what you describe.
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Unread 07-07-2015, 01:11 PM   #5
JWMan
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Quote:
Originally Posted by RockyClymer View Post
Master cylinder.

The master cylinder pump is replaced with a new one.

After replacing the master cylinder pump it was OK for few days, but the problem appeared again.

Is this something to do with the ABS controller?
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Unread 07-07-2015, 01:13 PM   #6
JWMan
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Quote:
Originally Posted by Neo1130 View Post
Master cylinder or air in the brake lines... I just replaced brake lines on a buddies Jeep a couple weeks ago because there was a split in the hard line that acted like what you describe.
Bleed out done on each wheel. There are no leaks. Brake lines appear in good condition.
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Unread 07-07-2015, 03:39 PM   #7
VEGASROBBI
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Quote:
Originally Posted by JWMan View Post
The master cylinder pump is replaced with a new one.
The Master Cylinder mounts on the brake booster which is mounted to the firewall, there is no Master Cylinder Pump I know of. There is a vacuum pump used on some JK's to increase vacuum to the booster under load. I am referring to a gas JK, not diesel.

The HCU(Hydraulic Control Unit) is mounted on the fenderwell along side the ABS module. The HCU contains the pump motor, valve body, accumulators, inlet valves, etc.
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Unread 07-07-2015, 07:49 PM   #8
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you have air in the ABS motor. take your jeep out o a dirt road and do about 5 or 6 complete stops form about 30 mph, then bleed the brakes. if you take your jeep into the dealer, they use a starscan tool to simulate the ABS motor functioning to bleed the brakes of all the air. the dirt road will save you the $ they will charge you to hook up the tool.
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Unread 07-07-2015, 11:02 PM   #9
JWMan
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Quote:
Originally Posted by VEGASROBBI View Post
The Master Cylinder mounts on the brake booster which is mounted to the firewall, there is no Master Cylinder Pump I know of. There is a vacuum pump used on some JK's to increase vacuum to the booster under load. I am referring to a gas JK, not diesel.

The HCU(Hydraulic Control Unit) is mounted on the fenderwell along side the ABS module. The HCU contains the pump motor, valve body, accumulators, inlet valves, etc.

I'm sorry if I misinterpreted, that's how the garage guy told me. Many thanks for correcting me.
My Jeep is gas not diesel
This is the part they replaced.

Is it that my HCU gone bad?
master-cylinder.jpg  
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Unread 07-07-2015, 11:04 PM   #10
JWMan
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Quote:
Originally Posted by JohnRodriguez View Post
you have air in the ABS motor. take your jeep out o a dirt road and do about 5 or 6 complete stops form about 30 mph, then bleed the brakes. if you take your jeep into the dealer, they use a starscan tool to simulate the ABS motor functioning to bleed the brakes of all the air. the dirt road will save you the $ they will charge you to hook up the tool.

Thanks. Let me give it a try
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Unread 07-08-2015, 12:27 AM   #11
rich6700
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Quote:
Originally Posted by JWMan
I'm sorry if I misinterpreted, that's how the garage guy told me. Many thanks for correcting me. My Jeep is gas not diesel This is the part they replaced. Is it that my HCU gone bad?
That's a picture of the master cylinder reservoir.
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Unread 07-08-2015, 06:51 AM   #12
jwmbishop
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they probably replaced master and reservoir - guys, he's in Dubai - we're loosing some in translation. He DID mean master cylinder (and it IS a pump lol).

I agree with air in the ABS pump.
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Unread 07-08-2015, 08:45 AM   #13
JWMan
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Quote:
Originally Posted by rich6700 View Post
That's a picture of the master cylinder reservoir.


Sorry guys, picture was inconclusive. It didn't copy the complete picture.

This is the complete unit. This was replaced.
mwsnap-2015-07-08-18_42_56.jpg  
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Unread 07-08-2015, 10:06 AM   #14
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Quote:
Originally Posted by JWMan View Post
I'm sorry if I misinterpreted, that's how the garage guy told me. Many thanks for correcting me.
My Jeep is gas not diesel
This is the part they replaced.

Is it that my HCU gone bad?
No worries I think we just need to make it clear what part you replaced. In a hydraulic system you have rams at both ends which move the fluid, in this case you have the master cylinder on one end and the caliper pistons on the other.

Many hydraulic systems have a hydraulic pump or in this case the ABS pump motor which is inside the hydraulic control unit.

I agree you should do a scan bleed to get rid of air in the ABS assembly after you have done a thorough manual bleed.

This probably no longer applies but back in the 1990's we had a lot of issues with the Kelsey Hayes ABS systems. The pedal would randomly drop to the floor and the truck would slowly roll to a stop it was very unnerving. The problem was low voltage: sometimes it would be from a weak battery or alternator but in most cases it was due to corrosion in the cables not supplying enough power to the hydraulic control unit, when the voltage would drop the unit would react by dumping pressure.
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Unread 07-08-2015, 02:24 PM   #15
Maertz
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It was a pain to bleed my abs unit. To bleed it takes a very expensive scan toll only shops and dealers normally have. I was successful in locking up my brakes on gravel roads activating the abs then bleeding my lines and repeat a few times...
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