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Old 02-15-2013, 09:26 AM
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brake pad and engine issues. 2012 JKU

first the braking issue. i believe my rotors are warped.

upon decelerating and braking, i feel the pressure oscillating in the pedal and through the gforce on my body. its like they push,loose,push,loose. like i have only half a rotor.the brake force varies at the same pedal force.

imagine a pringles chip as a rotor, thats how it seems this is caused


the engine issue is a what seems to be an intake and rpm issue.

i will clarify if the rpms vary of which im am unsure.

upon a slow acceleration into second gear(auto)feels as if the rpm is hoping. like i am oscillating the pedal. on off on off on off. i can hear the engine actually fluctuating the intake or power delivery through my exhaust. at the same pedal force, it will eventually power through the issue. but it seems as tho the engine is doing something likt this

Following is in reference to what seems like power or rpm. oscillating power, intake and exhaust sound. y axis is acceleration

from a stop to acceleration _______--__--__--__--__--
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Old 02-15-2013, 09:33 AM   #2
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For the brakes, I would check the fluid first. It is sounding like air in the lines. A warped rotor pulses very rapidly when applying brakes. Almost violently if they are very warped bad. The way you are explaining it is making me lean towards bleeding the system. Now the tranny. It is sounding like a torque converter. Like it's slipping.

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Old 02-15-2013, 09:59 AM   #3
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It could be an ABS sensor issue. Have the dealer check it out. It's most likely covered under warranty.
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Old 02-15-2013, 10:42 AM   #4
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Take you Jeep in. As a fellow 2012 JK unlimited owner, I am not having either of these issues. Another factor may be in mods done, if done poorly. Mine is stock.

Edit:

Other issues could be doing off roading without after event cleaning or maintenace. Have you mud bogged or gone through deep water?
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Old 02-15-2013, 10:42 AM
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i have great brake pressure when i need it, i assume its not a bleeding or air thing, i tend to stick with pad or rotor issues. and it is a relatively noticable pulsing..

the engine thing i want to sway agaisnt abs due to it does not affect tires or skipping in the tires or traction and brake application.

the torque converter thing... if i throttle out of it, it seems to torque the way through
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Old 02-15-2013, 11:02 AM   #6
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Water crossings can warp the rotors even on a relatively new vehicle. I agree with the others, I'd take it to the dealer.

The other possibility for both of your problems is the traction control system malfunctioning.
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Old 02-15-2013, 11:08 AM   #7
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"The other possibility for both of your problems is the traction control system malfunctioning."

Hence the suggestion that it might be an ABS sensor issue. If you are already having brake issues, there's a good possibility that the two are related.

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Old 02-15-2013, 11:20 AM   #8
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Quote:
Originally Posted by onetraveller View Post
"The other possibility for both of your problems is the traction control system malfunctioning."

Hence the suggestion that it might be an ABS sensor issue. If you are already having brake issues, there's a good possibility that the two are related.

Mike
Exactly. It's all related. Brake pulsing is what happens when ABS is activated.
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Old 02-15-2013, 12:16 PM   #9
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As a longtime aircraft electrician, 2 major problems often point to one source!
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Old 02-15-2013, 12:28 PM   #10
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For the pads if you think they are warped take them off and put them on a flat table, you will be able to see if they are warped or not. To see if there is any air in the lines bleed the brakes for a bit and see what the fluid looks like.

You need to do something to start eliminating potential problems.

No insight into the transmission though, have no experience with it.
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Old 02-15-2013, 01:38 PM   #11
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The pads don't warp, the rotors do and no you can't just take them off and look at them. Although even that isn't generally true. Most claims of warped rotors are actually caused by deposits of pad materials from overheating the brakes, then letting them sit still for too long.

Here's a great article on brake myths by Carroll Smith, a legend in race car engineering.

-Warped- Brake Disc and Other Myths

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Old 02-15-2013, 04:27 PM   #12
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yea, I meant to say rotors.

and that is a very interesting link. they did still mention the runout on the rotors, which would be noticeable if you place them on a flat surface correct?
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Old 02-15-2013, 05:34 PM   #13
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No, the difference is generally to small for the human eye to see. You have to gauge the rotor using a micrometer.

Here's an example from a Toyota technical document on the tolerances they consider acceptable for brake rotors and the rest of the rotating assemblies.

TOYOTA RUNOUT/VARIATION SPECIFICATIONS
Brake rotor runout = 0.002 - 0.004 in.(0.05 - 0.1mm) max.(refer to vehicle manual)
Brake rotor thickness variation = 0.0004 in.(0.01mm) max.
Tire runout (radial) = 0.039 in. (1.0mm) max.
Tire runout (lateral) = 0.047 in. (1.2mm) max.
Wheel rim runout (radial) = 0.019 in.(0.5mm) max.
Wheel rim runout (lateral) = 0.019 in.(0.5mm) max.
Hub runout (radial) = 0.002 in. (0.05mm) max.
Hub runout (lateral) = 0.002 in. (0.05mm) max.

http://www.toyotapartsandservice.com...ter/Brakes.pdf

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