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Old 08-17-2010, 04:55 PM   #1
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pulsation

here is my problem, this past weekend i put new universal joints on each side of the front axle, while i had it apart i put on new rotors and brake pads, after putting it all back together i was driving and when i stepped on the brakes the pedal pulsed about two inches, i took it all back apart and checked everything, i checked the rotors to make sure they are staright and they are, the pads are brand new, i have no idea what could cause this pulsing, any ideas???

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Old 08-17-2010, 04:58 PM   #2
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The first couple presses it probably will feel slightly off due the the pads setting... But if you still have a pulsing your rotors are probably warped. I assume they were new? Might want to check on a warranty swap. Also, if you don't have a firm pedal you may need to bleed the brakes.

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Old 08-17-2010, 05:13 PM   #3
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the rotors and pads were new and i put about 50 miles on it since i changed them and still got some pulsing but not quite as bad, now its down to about an inch to an inch and a half, will it eventually go away?
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Old 08-17-2010, 05:21 PM   #4
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What do you mean it's down to an inch and a half?? You mean that's how far down the pedal goes?
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Old 08-17-2010, 05:30 PM   #5
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now when i initially step on the pedal it will pulse the pedal upwards about an inch and a half and then go down and pulse back up and so on and so forth
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Old 08-17-2010, 05:52 PM   #6
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New rotors are not always true(may be warped when new). I know they should be, but i've seen to many times that they aren't, we do a light machine on new rotors before they are installed.
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Old 08-17-2010, 06:01 PM   #7
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Didi you open the brake lines at all.. add or remove fluid?
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Old 08-17-2010, 06:03 PM   #8
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No didnt touch the brake lines or the fluid.
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Old 08-17-2010, 06:22 PM   #9
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This might sound stupid but, did you damage one of the tone rings on the front axle shafts or move the ABS sensors? This is what will happen if you did. The pulsing is the ABS activating because it is no longer getting a signal from one or both of the front sensors and is basically acting as if both wheels have locked up every time you brake. If this is the problem I suggest you fix it right away, your braking distance will be significantly increased even on completely dry pavement. Mine did this exact thing when I accidently broke off a chunk of material from the tone ring on the front shaft.
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Old 08-17-2010, 07:39 PM   #10
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this may sound stupid but what is the tone ring? thats the end of the shaft that the universal joint goes into right? yes i did damage the driver side when i knocked out the old U-joint and i dont have ABS
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Old 08-18-2010, 12:14 AM   #11
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Did you relieve the stress in the U joints after putting them in the axle? Sometimes the caps are tight on the journal, making it hard to move.
Always, after you install a U-joint, whack the ears with a hammer - a stout blow - notice how the joint moves so much easier now. No, they will not loosen up by driving - you have to do it.
You might try whacking each ear now while still in place - use a long rod.

Of course you did check the runout on the disk while it's mounted.

Funny how the rumor is that rotors are warped from the factory. It stems from guys putting the new rotor on a lathe - by mounting it on cones. The test - mount it on the cones, machine it straight, dismount it all the way, re-mount it on the same cones - how did it get so warped again? You cannot duplicate it no matter how many times you remount it.
The factory uses a multimillion $ machine to make them, then a "mechanic" uses a $5000 lathe to correct them?

The best way to true them - use a "on-the-car" brake grinder that leaves a non-directional finish - not a lathe. That trues the rotor mounted on the bearings while mounted in place as it will be in service.
If you do use a lathe, you have to get rid of the thread marks the lathe left. Else it will cause the pads to follow the thread marks.
Look close at your rotors, if you can see the thread marks cut by a lathe, that could be the pulsation - the shoes keep moving following the grooves, pushing the caliper back and forth - making the pedal pulsate.

Seems like Jeeps and Cadillac are most prone to it.
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Old 08-18-2010, 05:57 PM   #12
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What is the runout on the disk? And how do i check it? Can i hit the ears while it is all assembeled or should i dismantle it all and hit it so it has room to adjust itself?
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Old 08-18-2010, 07:12 PM   #13
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Did you whack the bearings out with a hammer you could have bent one of them . Did you torque the nut on the axle . This is the preload for the bearing or it could be loose and wobble
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Old 08-18-2010, 07:54 PM   #14
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i didnt take the bearings apart, i took the three bolts out that hold the bearing and axle in the housing and slid the bearing, universal joint, and axle all out together still assembeled then proceeded to take the universal joints apart, i did bend the end of the axle when i was taking the old joint out but i bent it back and the new universal joint fit in, so i assumed it is in line good enough, i dont get a vibration or anything when driving, just the pulsing when i try to stop
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Old 08-19-2010, 07:21 AM   #15
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What I meant was after you took the 3bolts out did you use a hammer to remove the bearing assembly ? Hitting on the ring that the lug studs are on . Sometimes the bearing assembly comes out very hard from the knuckle if that ring is bent the rotor won't lay flat and will wobble . You can take your wheel off and put lug nuts on and tighten them up, if you have access to a dial indicator check it for runout if you have warpage with the rotor on , take the rotor off and check the bearing. This should show you your problem
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Old 08-19-2010, 08:49 AM   #16
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It was tough to get out but what i did was use a chizel and put it between the brake dust shield and the bearing and tapped it on all three points, i was finally able to get it out but i didnt hit anything on the bearing, i just wedged it away from the housing where the three bolts were
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Old 08-19-2010, 06:19 PM   #17
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new news, so i went through everything and i was going nuts so on a whim i was wondering if maybe everything in the front end was ok and it had something to do with the back brakes which are drum brakes, so when i was driving i stepped on the clutch and threw it in nuetral as i coasted i pulled up on the emergency/parking brake and when i did that the jeep pulsed the same as it does when i step on the brake pedal so that "should" mean that the pulsing is actualy from the rear brakes but why would i have not felt that before i did everything in the front end. I did not touch the back end at all
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Old 08-19-2010, 06:53 PM   #18
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A tone ring is found on the front outer stub shafts and the rear axle shafts, they look like this:
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Old 08-19-2010, 06:55 PM   #19
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If you have damaged one this is your problem.
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Old 08-20-2010, 12:29 AM   #20
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Applying the parking brake and experiencing the same pulsation in the pedal?

Time to take the rear brakes apart. Did you remove a wheel? Lug nuts loose?

Sounds to me like the drum is either "off center" or badly warped.
A visual inspection should see it.

Remove tire/wheel - rotate the brake drums by hand - you should "feel" which one is the culprit. If you can't tell, apply the parking brake very lightly and rotate.
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Old 08-21-2010, 01:29 PM   #21
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ok took the back tires off and found one of the drums had a spot that kept hitting so replaced the drums and fixed it a bit but i decided to take the front tires off while i had the jeep up on jack stands and put the jeep in 4 low and let the clutch out and put a fixed object on the side of the rotor and found that the rotor is not true, its off about 1/16" to an 1/8" so i am going to get it turned so its true, didnt know if napa would take them back so i will do it myself. but after that the pulsing will hopefully be gone

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