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Unread 01-08-2014, 07:44 AM   #1
supersport126
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Problems with brakes, please help

Ok, since we've gotten cold weather in Michigan first start of the morning when you depress the brake pedal it's rock hard almost can't push it in.
Now that the temperature is 10 or lower when you pull away you can press the brake pedal and it just does not stop until the vehicle warms up a little bit. We've got 72,000 miles but every time it's serviced they say that the brake pads look good I think there might be a vacuum leak our something I'm not sure. After 5 to 10 minutes of driving the brake pedal feels normal and everything is back working okay

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Unread 01-08-2014, 08:30 AM   #2
Dave2002ti
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Brake Fluid

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Originally Posted by supersport126 View Post
Ok, since we've gotten cold weather in Michigan first start of the morning when you depress the brake pedal it's rock hard almost can't push it in.
Now that the temperature is 10 or lower when you pull away you can press the brake pedal and it just does not stop until the vehicle warms up a little bit. We've got 72,000 miles but every time it's serviced they say that the brake pads look good I think there might be a vacuum leak our something I'm not sure. After 5 to 10 minutes of driving the brake pedal feels normal and everything is back working okay
Needs to changed and flushed. You should have the brake fluid changed every 24mos or sooner depending on how wet and humid your location is. Brake fluid absorbs water. The OEM brake pads should not need to warm up unlike some high performance and racing pads like Metalmasters. As you back out the driveway you can keep light pressure on the brakes to heat up the pads. However, you description doesnt sound normal. I would bring your vehicle in and drop it off overnight and let it sit outside so they can duplicate the problem
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Unread 01-08-2014, 09:21 AM   #3
loveracing1988
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Quote:
Originally Posted by Dave2002ti View Post
Needs to changed and flushed. You should have the brake fluid changed every 24mos or sooner depending on how wet and humid your location is. Brake fluid absorbs water. The OEM brake pads should not need to warm up unlike some high performance and racing pads like Metalmasters. As you back out the driveway you can keep light pressure on the brakes to heat up the pads. However, you description doesnt sound normal. I would bring your vehicle in and drop it off overnight and let it sit outside so they can duplicate the problem
While in theory this is true, outside of racing how often have you ever heard of brake fluid freezing or boiling from water being in the brake fluid. Between me and everyone I work with there is over 100 years of working on vehicles not one has ever heard of that outside racing and people towing down mountains riding the brakes.
If I had to venture a guess the booster is getting moisture in it somehow. I've noticed on my wifes some days you get in to start it and it will still have vacuum, other days it doesn't, if the vacuum can escape moisture can get in.
The only other possibility would be frozen calipers and rotors from driving through deep snow, I would say slush but since it hasn't gotten above 2 degrees since monday I would say that you haven't hit slush.
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Unread 01-08-2014, 09:53 AM   #4
Dave2002ti
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Pedal Feel

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Originally Posted by loveracing1988 View Post
While in theory this is true, outside of racing how often have you ever heard of brake fluid freezing or boiling from water being in the brake fluid. Between me and everyone I work with there is over 100 years of working on vehicles not one has ever heard of that outside racing and people towing down mountains riding the brakes.
If I had to venture a guess the booster is getting moisture in it somehow. I've noticed on my wifes some days you get in to start it and it will still have vacuum, other days it doesn't, if the vacuum can escape moisture can get in.
The only other possibility would be frozen calipers and rotors from driving through deep snow, I would say slush but since it hasn't gotten above 2 degrees since monday I would say that you haven't hit slush.
Although fluid might not it boil or freeze the water in the fluid will effect the feel of the brake pedal. Brake fluid does need changing in the OP's WK and that will eliminate one possibility and relatively cheaply since he is out of warranty.

One of the reasons you change brake lines from rubber to an Earl's brake line is prevent the OEM brake lines from swelling. The Earl's line gives you a more consistent pedal feel on both the street and the track. Outside temp does have an effect.
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Unread 01-08-2014, 10:01 AM   #5
2kg4u
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Brake fluid is hygroscopic, which means moisture is absorded into the brake fluid, not suspended as drops that can freeze and restrict flow. Changing brake fluid is an oft overlooked maintenance item and should be done, but I don't think this issue has anything to do with old fluid.

Is your Jeep stored inside or outside? Is there a snow build up in and around your wheels? I think loveracing's comments are 100% spot on. Most likely candidate IMO is frozen calipers that free up once they get warm. If you want to narrow it down, try hitting all the calipers for a few minutes with a heat gun prior to starting and driving your jeep. If that resolves the problem, one nice warm day next summer you should disassemble, clean and lubricate the brake assemblies. Grease, in the right places, will displace water and prevent freeze ups.
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Unread 01-08-2014, 10:18 AM   #6
Dave2002ti
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One other thing

What about the parking brake? It could have moisture in it and be sticking since its the old foot and cable operated type???

I once had mine freeze stuck on an old Rabbit. Driving broke it loose but flat spotted the tire something awful. It was raining then got cold with temps at or around zero.
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Unread 01-08-2014, 11:36 AM   #7
97HMCS
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Quote:
Originally Posted by supersport126 View Post
Ok, since we've gotten cold weather in Michigan first start of the morning when you depress the brake pedal it's rock hard almost can't push it in.
Now that the temperature is 10 or lower when you pull away you can press the brake pedal and it just does not stop until the vehicle warms up a little bit. We've got 72,000 miles but every time it's serviced they say that the brake pads look good I think there might be a vacuum leak our something I'm not sure. After 5 to 10 minutes of driving the brake pedal feels normal and everything is back working okay
Is the problem with your CJ7?
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Unread 01-08-2014, 12:09 PM   #8
loveracing1988
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Quote:
Originally Posted by Dave2002ti View Post
What about the parking brake? It could have moisture in it and be sticking since its the old foot and cable operated type???

I once had mine freeze stuck on an old Rabbit. Driving broke it loose but flat spotted the tire something awful. It was raining then got cold with temps at or around zero.
That wouldn't cause a hard brake pedal though. That would cause spme funky vehicle handling but the pedal would still move like normal.
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Unread 01-08-2014, 02:23 PM   #9
supersport126
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This response is to everyone who has posted,
It's not ice or frozen calipers because it's happened during no snow days. This is a 2012 with 73k, not my old 7 lol. First thing in the morning when you have to depress the brake pedal to start the vehicle, it's hard as a rock. You couldn't push it in an inch if you wanted to. As soon as it starts the pedal drops and feels normal. Then pulling away I have good pedal when slowly stopping, like coming up to a stop sign....BUT if you pushed on the pedal hard the breaks will not lock up they just slowly stop. After 5 minuets or so everything is back to normal
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Unread 01-08-2014, 03:24 PM   #10
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Quote:
Originally Posted by Dave2002ti View Post
What about the parking brake? It could have moisture in it and be sticking since its the old foot and cable operated type???

I once had mine freeze stuck on an old Rabbit. Driving broke it loose but flat spotted the tire something awful. It was raining then got cold with temps at or around zero.
The Wk2 mechanical parking and hydraulic brakes are two separate systems, operating independently, including pads, rotors, drums. Although many car companies decide to double up on the rear caliper function, Jeep chose not too..
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Unread 01-08-2014, 03:30 PM   #11
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I think loveracing may be on the right track here. Perhaps supersport always had a small booster vacuum leak, which gets closed off (frozen over) until the engine compartment warms up.. or there is a bit of ice forming within the booster, preventing it from doing its job. A vacuum booster not working properly can cause the symptoms the OP explained.... perhaps a frozen check valve. Have the pads ever been replaced? 77,000 miles on the rear seems overdue from what I've read here.

This is what the service manual suggests:

HARD PEDAL OR HIGH PEDAL EFFORT

A hard pedal or high pedal effort may be due to lining that is water soaked, contaminated, glazed, or badly worn. The power booster, check valve, check valve seal/grommet or vacuum leak could also cause a hard pedal or high pedal effort.

These are the test procedure from the service manual:

DIAGNOSIS AND TESTING - MASTER CYLINDER/POWER BOOSTER

1.Start the engine and check the booster vacuum hose connections. A hissing noise indicates a vacuum leak. Correct any vacuum leaks before proceeding.

2.Stop the engine and pump the brake pedal until all vacuum reserve in the booster is depleted.

3.Press and hold the brake pedal under light foot pressure. The pedal should hold firm. If the pedal falls away, there may be an external leak or the master cylinder is faulty (internal leakage).

4.Start the engine and note pedal action. It should fall away slightly under light foot pressure, then hold firm. If no pedal action is discernible, the power booster, vacuum supply or vacuum check valve is faulty, proceed to the POWER BOOSTER VACUUM TEST.

5.If the POWER BOOSTER VACUUM TEST passes, rebuild the booster vacuum reserve as follows: Release the brake pedal. Increase engine speed to 1500 RPM, close the throttle and immediately turn off the ignition to stop the engine.

6.Wait a minimum of 90 seconds and try brake action again. The booster should provide two or more vacuum assisted pedal applications. If the vacuum assist is not provided, the booster is faulty.



POWER BOOSTER VACUUM TEST

1.Connect a vacuum gauge to the booster check valve with a short length of hose and T-fitting.

2.Start and run the engine at curb idle for one minute.

3.Observe the vacuum supply. If the vacuum supply is less that 12 inches HG (406 millibars), repair the vacuum supply.

4.Clamp the hose shut between the intake vacuum source and the check valve.

5.Stop the engine and observe the vacuum gauge.

6.If the vacuum drops more than one inch HG (33 millibars) within 15 seconds, the booster diaphragm or check valve is faulty.



POWER BOOSTER CHECK VALVE TEST

1.Remove the power booster check valve from the power booster.

2.Using a hand operated vacuum pump, apply 15-20 inches HG (508-677 millibars) vacuum at the booster side of the check valve.

3.The vacuum should hold steady. If the gauge on the pump indicates vacuum loss, the check valve is faulty and should be replaced.
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Unread 01-08-2014, 06:46 PM   #12
supersport126
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Quote:
Originally Posted by ColdCase
I think loveracing may be on the right track here. Perhaps supersport always had a small booster vacuum leak, which gets closed off (frozen over) until the engine compartment warms up.. or there is a bit of ice forming within the booster, preventing it from doing its job. A vacuum booster not working properly can cause the symptoms the OP explained.... perhaps a frozen check valve. Have the pads ever been replaced? 77,000 miles on the rear seems overdue from what I've read here. This is what the service manual suggests: HARD PEDAL OR HIGH PEDAL EFFORT A hard pedal or high pedal effort may be due to lining that is water soaked, contaminated, glazed, or badly worn. The power booster, check valve, check valve seal/grommet or vacuum leak could also cause a hard pedal or high pedal effort. These are the test procedure from the service manual: DIAGNOSIS AND TESTING - MASTER CYLINDER/POWER BOOSTER 1.Start the engine and check the booster vacuum hose connections. A hissing noise indicates a vacuum leak. Correct any vacuum leaks before proceeding. 2.Stop the engine and pump the brake pedal until all vacuum reserve in the booster is depleted. 3.Press and hold the brake pedal under light foot pressure. The pedal should hold firm. If the pedal falls away, there may be an external leak or the master cylinder is faulty (internal leakage). 4.Start the engine and note pedal action. It should fall away slightly under light foot pressure, then hold firm. If no pedal action is discernible, the power booster, vacuum supply or vacuum check valve is faulty, proceed to the POWER BOOSTER VACUUM TEST. 5.If the POWER BOOSTER VACUUM TEST passes, rebuild the booster vacuum reserve as follows: Release the brake pedal. Increase engine speed to 1500 RPM, close the throttle and immediately turn off the ignition to stop the engine. 6.Wait a minimum of 90 seconds and try brake action again. The booster should provide two or more vacuum assisted pedal applications. If the vacuum assist is not provided, the booster is faulty. POWER BOOSTER VACUUM TEST 1.Connect a vacuum gauge to the booster check valve with a short length of hose and T-fitting. 2.Start and run the engine at curb idle for one minute. 3.Observe the vacuum supply. If the vacuum supply is less that 12 inches HG (406 millibars), repair the vacuum supply. 4.Clamp the hose shut between the intake vacuum source and the check valve. 5.Stop the engine and observe the vacuum gauge. 6.If the vacuum drops more than one inch HG (33 millibars) within 15 seconds, the booster diaphragm or check valve is faulty. POWER BOOSTER CHECK VALVE TEST 1.Remove the power booster check valve from the power booster. 2.Using a hand operated vacuum pump, apply 15-20 inches HG (508-677 millibars) vacuum at the booster side of the check valve. 3.The vacuum should hold steady. If the gauge on the pump indicates vacuum loss, the check valve is faulty and should be replaced.
I will run this test ASAP, thank you sir. Oh and all brakes are original. All highway miles
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Unread 01-08-2014, 08:33 PM   #13
tjkj2002
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Quote:
Originally Posted by loveracing1988 View Post
While in theory this is true, outside of racing how often have you ever heard of brake fluid freezing or boiling from water being in the brake fluid. Between me and everyone I work with there is over 100 years of working on vehicles not one has ever heard of that outside racing and people towing down mountains riding the brakes.
If I had to venture a guess the booster is getting moisture in it somehow. I've noticed on my wifes some days you get in to start it and it will still have vacuum, other days it doesn't, if the vacuum can escape moisture can get in.
The only other possibility would be frozen calipers and rotors from driving through deep snow, I would say slush but since it hasn't gotten above 2 degrees since monday I would say that you haven't hit slush.
Seen it a few times here in CO with people not used to mountain driving.In most cases when it happens the shop will never prove it as the problem has solved itself(cooling of the fluid or melting of the ice).

I have to 100% agree with Dave2002ti,you really need to have the fluid flushed often with newer ABS systems as corrosion will effect brake feel.The older systems have little or no sub-systems but a WKII has many in the brakes system.Get a brake fluid test strip and test the copper content,that will tell you the level of corrosion in the system from the aluminum and ABS components corroding.More corrosion(higher copper content) means more water in the system.
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Unread 01-08-2014, 09:03 PM   #14
ColdCase
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Quote:
Originally Posted by tjkj2002 View Post
I have to 100% agree with Dave2002ti,you really need to have the fluid flushed often with newer ABS systems as corrosion will effect brake feel.The older systems have little or no sub-systems but a WKII has many in the brakes system.
I don't think this has anything to do with the OP's issue. The newer Brake systems are much better sealed, with better anti-corosion practices as well as filled from the factory with higher quality fluid. Flushing fluid often is a thought left over from decades ago. No question the fluid needs to be kept an eye on, but thats not any different than years ago.

Jeep no longer mentions flushing out brake fluid as part of routine maintenance... wonder why?
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Unread 01-08-2014, 09:21 PM   #15
supersport126
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Jeeps only 2 years old, shouldn't have too much corrosion!
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