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Unexplainable Pulsating Brake Pedal


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8 replies to this topic

#1 jmoss5723

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Posted 09 July 2016 - 09:49 PM

My wife's 2002 Outback H6 has had a pulsating brake pedal ("warped rotor" feeling) for almost a year. I've basically replaced everything, but the problem persists. I don't know what it is that I'm missing.

It started after I did a full change of pads and rotors on the front last fall (only 1 or 2k miles ago). I installed ceramic pads and told her to do the simple break-in procedure when she drove it later that day. Well, she didn't do it and I blamed the pulsing on that and told her it was her own fault and that she could live with it.

Last week, I needed to change the rear pads and I did the rear rotors while I was at it. Nothing changed in the pulsing pedal, but I didn't expect it to. Today I changed the front rotors and I think the pulsing is now WORSE!

With new rotors all around, no stuck calipers, etc. what could be causing this?!

#2 Bushwick

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Posted 10 July 2016 - 12:12 AM

Are you spraying brake cleaner on the rotors to remove the protective grease that's applied to prevent rusting while in the box? Has the car been curbed at all? Is there a broken belt on one of the tires? Is there a reason why you are using ceramic on a daily driver? 

 

When you replaced the rotors, did you carefully inspect the axle hubs for scaling rust that might be pushing the rotor out slightly? Or conversely, a gouge in the hub's mating surface that might causing a few thousandths lip? Are the balljoints, tierods, etc. solid and tight? 

 

Wouldn't hurt to take it to a shop that does free inspections and see what they say. Bet you'd feel like a complete rump roast if she wrecked and it was actually your fault for overlooking something.....



#3 1 Lucky Texan

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Posted 10 July 2016 - 10:05 AM

^^^ good ideas - I have read of an issue with rust/debris caught between the rotor and hub causing oscillation.

 

worn inner tie rods can exarcerbate a bad tire or brake problem. Look for broken caliper bolts/brackets too.

 

But, 'warped' rotors are most often caused by uneven pad deposits, occasionally by altered tempering of rotor alloy(cementite), they are almost never 'potato chopped' nor have significant non-parallelism.

 

if all the above issues have been ruled-out, one thing to try is a bedding in procedure (you MUST do any bed-in with the understand that the car can NEVER be held at a stop with the pads when the brakes are heated-up, be certain traffic, cops and road conditions will alow a very good cool-down run)

. An easy 'moderately aggressive ' one is , maintain 30-40 mph and left-foot-drag the brake. maintain speed, drag the brake for 3-4 blocks, then, cool down with no stopping for 1/2 mile. If you MUST come to a complete stop - use the hand brake for the final 2mph and to hold the car.

 

If, after a bedding-in routine the problem is WORSE - that points to bad rotor conditions that are unlikely to be solved by cutting (cementite)

 

If the problem is better but not solved, a repeat or a more aggressive bedding-in may be required.

 

good reading at StopTech, here's one on warped brakes - http://www.stoptech....and-other-myths


Edited by 1 Lucky Texan, 10 July 2016 - 10:43 AM.


#4 Bobaru71

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Posted 10 July 2016 - 10:33 AM

Sounds like lateral run-out --> http://www.tirerevie...re-they-happen/

 

I'm going through this myself. Have scheduled it to go back in and for the tech to use an on-car brake lathe this time.



#5 jmoss5723

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Posted 10 July 2016 - 05:36 PM

No idea what changed, but today when I got in the car, everything was perfect.

Last night I put on the rotors, drove it, and the pulsing was horrible. Today it was totally gone. All I did was hope and pray I'd figure it out, but I didn't "fix" anything. Odd.

#6 idosubaru

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Posted 10 July 2016 - 06:39 PM

Can you describe the symptom if it happens again? It's positively like pulsating brakes?

front control arm rear transverse bushing or capture nut can exhibit pulsating while braking as well but are slightly different in tone.

#7 jmoss5723

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Posted 10 July 2016 - 10:05 PM

If it happens again, I'll report back.

It was doing it for almost a year since right after a brake job. Definitely brake pulsing. But it seems to be all better now. Drove 50 miles or so today with no issues at all.

#8 1 Lucky Texan

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Posted 22 August 2017 - 02:51 PM

jmoss - how's the car doing?



#9 jmoss5723

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Posted 23 August 2017 - 03:54 PM

jmoss - how's the car doing?

Brake pulsing never came back. I still have no idea what happened there.

 

The car was sold a few months back to buy a minivan for my growing family. It was a bummer to have to sell it. It was probably the best subaru I've had yet. It's still rolling around though. I saw it on Sunday, a little dirty, but no worse for wear.






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