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Unread 07-19-2014, 11:20 AM   #1
BarneyWrangler
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Brakes at 44000?

I just had the Jeep (a 2012 JKU, 44000 miles) in to the dealer for the transmission pipe recall (that took at least 6 months for the part). The service guy came out and told me that I needed rear brakes, with maybe 2mm-3mm left on the pads/rotors. His explanation was that the proportional valve for the brakes puts most of the braking force on the rear, so those tend to go first. Has anybody else experienced this? I've always felt the brakes were weak, maybe this is why.

The Jeep's a daily driver, with a fair amount of stop-and-go in traffic south of Boston.

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Unread 07-19-2014, 11:43 AM   #2
HOKIES2010
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If they were your first set at 44k you made it longer than alot of people. mine went at 35k.
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Unread 07-19-2014, 12:36 PM   #3
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Same for me as HOKIES2010 although that was on my former ’08. My current Jeep has a ways to go as far as the mileage goes. And yes, it is very common for the JK brakes (rears) to go by then although a shocker in the beginning.
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Unread 07-19-2014, 04:18 PM   #4
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44K is awesome! Yes the service guy is on target for his explanation - however just slightly missing the mark.

The JK brakes are proportioned via the ABS system - the prop valve only comes into play in a failure\malfunction of the ABS system. As the stability and traction control calls for - more back brake is almost ALWAYS used than in older systems with a set 60/40 valve. So even if your standing on the gas - if you turn hard enough that the two rear wheels differential speeds are wide enough - the system would slightly engage the brakes on the wheel spinning fastest to keep the vehicle from skidding - if a tire breaks LOOSE the TC would engage the brakes on that wheel to prevent spin. And if you've ever used hill decent assist - you can feel the backs are working a ton more - simply because if the fronts lockup - you cant steer.

Subaru AWD eats ITS backs in about 18-22K so the JK average of 30k is NOT bad... but yes it goes against what us old schoolers expect - the proportion to ALWAYS be 60f/40r when the computer can go as hard as 20F/80r if needed!
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Unread 07-21-2014, 06:59 AM   #5
BarneyWrangler
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Thanks for the info guys!! Time to see my mechanic...
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Unread 07-21-2014, 08:58 AM   #6
HOKIES2010
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Quote:
Originally Posted by BarneyWrangler
Thanks for the info guys!! Time to see my mechanic...
Save a ton of money and do it on a weekend. Not a hard job to do at all.
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Unread 07-21-2014, 10:37 AM   #7
MrSmiley
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Quote:
Originally Posted by HOKIES2010
Save a ton of money and do it on a weekend. Not a hard job to do at all.
x2 only takes an hour or two to change the brakes
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Unread 07-21-2014, 10:54 AM   #8
jwmbishop
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Originally Posted by HOKIES2010 View Post
Save a ton of money and do it on a weekend. Not a hard job to do at all.
Just be sure to set an appointment for your machine shop to turn rotors or you could end up still on jackstands in the driveway come monday when its time to go to work...
neglecting to turn em?
IMO and experience, that's worse than continuing to run the old pads until you can afford or have time to turn rotors - there is NO WAY the bedding on the rotors matches the new pads material - even IF the same pad part # - heat alters the pads over their life and inconsistencies across production runs can be slightly different. So the old bedding (shredded off particles of brake pad packed into the pores of the rotor at approximately .010 depth at micro level) is "cured" different than the new bedding - improperly bedded brakes can have a ton of problems. New pads on unturned rotors - the new pad material never shreds off into the pores as the OLD material is still in them - so you now have two differing materials - that may or may not generate the friction potential. Oh yea - they stop you at the light and most folks couldn't tell the difference. But pads are designed to achieve a low temp and not exceed an upper. If your material mismatch does not generate enough friction to reach the low temp - brakes are NOT as effective as they could be. Same if the mismatch now generates TOO MUCH - only now you have a risk of fracturing rotor, boiling brake fluid or just plain fading to nada while still trying to get stopped. And will they be good enough if your family's life depends on that last two inches of stopping distance? Not a risk I take with MY wife and kids!

It scares me knowing I have to share the road with people who drink 20.00 worth of beer while justifying saving 20.00-30.00 in not performing a PROPER brake job - and could easily be the one who takes out MY family.
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Unread 07-21-2014, 10:56 AM   #9
HOKIES2010
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Originally Posted by jwmbishop View Post
Just be sure to set an appointment for your machine shop to turn rotors or you could end up still on jackstands in the driveway come monday when its time to go to work...
neglecting to turn em?
IMO and experience, that's worse than continuing to run the old pads until you can afford or have time to turn rotors - there is NO WAY the bedding on the rotors matches the new pads material - even IF the same pad part # - heat alters the pads over their life and inconsistencies across production runs can be slightly different. So the old bedding (shredded off particles of brake pad packed into the pores of the rotor at approximately .010 depth at micro level) is "cured" different than the new bedding - improperly bedded brakes can have a ton of problems. New pads on unturned rotors - the new pad material never shreds off into the pores as the OLD material is still in them - so you now have two differing materials - that may or may not generate the friction potential. Oh yea - they stop you at the light and most folks couldn't tell the difference. But pads are designed to achieve a low temp and not exceed an upper. If your material mismatch does not generate enough friction to reach the low temp - brakes are NOT as effective as they could be. Same if the mismatch now generates TOO MUCH - only now you have a risk of fracturing rotor, boiling brake fluid or just plain fading to nada while still trying to get stopped. And will they be good enough if your family's life depends on that last two inches of stopping distance? Not a risk I take with MY wife and kids!

It scares me knowing I have to share the road with people who drink 20.00 worth of beer while justifying saving 20.00-30.00 in not performing a PROPER brake job - and could easily be the one who takes out MY family.
I would just change the rotors
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Unread 07-21-2014, 11:07 AM   #10
jwmbishop
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Originally Posted by HOKIES2010 View Post
I would just change the rotors
I usually want to - but if I can get a turn on each one - that's significant over life of vehicle. My caddy is on its 6th set of brakes and I have only had to buy 5 rotors - 25% replacement rate - of course it's rotors are at best 75.00 bucks each...

A wilwood engineer once told me - when they turn the rotor the cast iron has rended away - that is left a fuzziness about .0005 tall. That fresh surface is "closed" when stacking the rotors for storage\shipment - or if any moisture contaminated during storage. He recommended at least a .003 pass on the lathe pre installation. Especially after a mock up assembly etc. Yea I know - that applies to high end racing brakes - but the work effect of cast does remain the same and since that enlightenment have always been tempted to turn even new rotors (although admittedly do not).
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