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Old 08-28-2006, 05:08 AM   #1
Tibfighter
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Default New Power Slot rotors/Hawk HPS pads... knocking sound?!?!

Well, got my new Power Slot rotors installed on all four corners on Friday and put in new Hawk HPS pads at the same time..... and over the last few days I have suffered through the slow break-in stage.

Well, today when driving down the highway I noticed an obvious knocking sound when I apply the brakes, particularly when I am below 40KM/h.. sometimes it seems to go away when the brakes have warmed up but othertimes it's always there. I can't tell for sure where the sound is coming from but it feels like I can feel it through the brake pedal. It's a consistent noise-noise-noise-noise until I lift off the pedal. It's like a soft thud or knocking sound.

Any ideas??? I hate diagnosing sound issues myself, so this is bugging me.

2004 STi w/ Power Slot slotted rotors and Hawk HPS pads.
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Old 08-28-2006, 10:10 AM   #2
Uncle Scotty
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pad leading edge catching in the edge of the slot(s) and making that noise.....it should subside in a couple hunderd km
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Old 08-28-2006, 11:55 AM   #3
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I have the same noise. I installed HPS w/ Brembo blanks on all four corners this weekend. This is on a WRX and I also upgrade the rear to H6.

I found a bunch of posts saying that it's pad movement, but I don't think this is what is happening to you and me.

It could be what uncle scotty said I don't think it is because you would have heard it before today.

I am hoping that it is:
a loose bolt
loose strut top nut(s)

good luck and let me know if you find something
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Old 08-28-2006, 04:07 PM   #4
Tibfighter
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Uncle Scotty, at first thats what I thought it was. Now I'm just not so sure.... the sounds occurs in a consistent enough pattern that you'd think it could be that... but hmmmm....

Now for the first few days I had driven very lightly and braked very lightly. Now before I parked prior to the issue arising, I had come to a pretty quick stop to avoid a car that had stopped in the middle of the street. Nothing extreme... just harder than I had been braking prior to that.
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Old 08-28-2006, 04:28 PM   #5
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.......drive the car 'normally' for a week or 2......then 'bed in' the pads and let us know wassupwidat
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Old 08-29-2006, 05:16 PM   #6
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...I'm gonna take it to my buddies shop tomorrow and see if they can spot anything obvious. Clearance doesn't seem to be an issue anywhere and everything is tight.
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Old 08-29-2006, 05:22 PM   #7
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Quote:
Originally Posted by Tibfighter View Post
...I'm gonna take it to my buddies shop tomorrow and see if they can spot anything obvious. Clearance doesn't seem to be an issue anywhere and everything is tight.
....d00000000d....my car did the SAME thing when I put slotted rotors on with new pads......it was preatty much gone after a week or 10 days
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Old 08-29-2006, 05:44 PM   #8
jim1969
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do slotted rotors make more noise than blanks?
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Old 08-29-2006, 11:20 PM   #9
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Quote:
Originally Posted by Uncle Scotty View Post
....d00000000d....my car did the SAME thing when I put slotted rotors on with new pads......it was preatty much gone after a week or 10 days
Really????????????????????????????

That makes me feel better. It's weird, I can drive for 5-10 minutes before it starts making the noise....

I just did a partial bed-in process again. 60-20, 60-20, 60-20.... and it was biting HARD now... really nice! but then the knocking sound promptly came back.
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Old 08-30-2006, 12:30 AM   #10
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I believe I had the same knock sound as yours. I installed over the weekend and all weekend long was the break in. only on semi hard brakes would the knock occur.

Today I went under the car and check all the bolts. All was good. So with knowing that I took her out. Did a few hard brakes, no knock. Ok... took it to about 60-70 and got on the brakes hard. No knock.

From that point on, I've put on the knock has stopped.
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Old 09-03-2006, 12:48 AM   #11
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That's interesting. I get it at the same time.... only during semi-hard-to-hard braking... but some days I get nothing.

It sounds like somebody has stuck a hockey card in the spokes of a bike... the slower I am the slower the thuds, etc.
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Old 09-03-2006, 03:09 AM   #12
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I conacted and was advised by dba, when I bought their slotted rotors, that when using 'green' pads and 'green' rotors together....that any 'bedding' should be done 'after a couple hundred km' to allow for seasoning of the individual components.

you may have got pad deposits on one section of one rotor.
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Old 09-03-2006, 12:18 PM   #13
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I have the same setup as you (04 STi, Powerslots, HPS). My brakes will make a 'pop' when I first apply them in the morning, or after driving for a bit, but it's not a constant sound. If I get on them hard from a high speed, it makes a "whirring" sound.
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Old 09-23-2006, 01:55 PM   #14
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Hello everybody....

I finally got frustrated with not being able to figure this out and I took the car to the dealership since I needed an oil change anyways....I dropped it off in the morning and came back at about 5pm to pick it up. The lady who runs the service department came over and told me my car was "weird," and explained that despite the techs working on my car the entire day (they did!) they could not find the source of the problem. During the course of the day, they swapped out almost every component from my front end, including axels, etc., in an effort to track down where the knocking sound was coming from. They took apart the brakes and noted that the rotors were all mint and that the break-in/bed-in process appeared to have gone perfectly.

First, some SERIOUS props to Saunders Subaru in Victoria, B.C., for their efforts. They worked all day on my car, charged me nothing for their efforts, and gave me my car back with the promise that they were going to do all they could to research the problem and find me a quick solution!!! Now that is service, despite the fact that they are working on a car sporting aftermarket springs, rotors and pads. The techs were awesome and brought me into the shop to show me what they had done, what they thought it may have been and laid out a plan to get things resolved as quickly as possible.

As it stands, they have not attempted to swap out the hubs/bearings or rotors to see if that fixes things as they did not have those parts on hand. But given that the rotors are all in mint condition it's doubtful that they are causing the problem. The techs also found that the loud knocking/banging sound is coming exclusively from the front driver's side of the car and they admitted themselves that it is "bad..." but not a safety concern.

Anyways, just an update incase anybody else ever experiences this and just some appreciation for the service guys at my dealership!
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Old 09-23-2006, 07:36 PM   #15
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....well...in light of all of the above.....I'd say that a bad wheel bearing is a good bet....
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Old 12-08-2006, 01:18 AM   #16
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Any updates Tibfighter? Very curious as to any possible solutions.
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