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Old 05-21-2007, 06:01 PM   #1
REX8
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Default Let's Find An Answer To This Semi-Common Problem

Problem: The mysterious rear rotor lip rubbing on the ebrake backing plate issue.

Every few months this problem appears on the forums, never a good answer given. No explanation has been found. Problem usually starts as a grinding while driving or turning. Sometimes AFTER having new rotors installed, and also, like myself, the problem arose for the first time after 10k miles on a set of rotors. Here's the issue.



^^^ Said rotor lip (in the middle, rusted over a bit)

Subaru techs have posted that when installing rear rotors on Impreza's it has become standard practive to machine or grind down this rotor lip to prevent rubbing. Fine, I'm just looking for a better solution.

When I can get to a mill, I take the 1/8" off the rotor lip needed to stop the noise...when I can't get to one...I have to do this:



^^^Cut away the bottom of the backing plate where the rotor rubs.

I'd just like to know why the problem would all of the sudden occur. Its NOT WHEEL BEARINGS and not bent hubs. What gives. I know I'm not alone.

I've had rubbing with OEM rotors, DBA H6 rotors (after 10-15k), and generic H6 rotors.

I know people have also had this problem with WRX sized rears, so I don't THINK its a difference with H6 rotor dimensions vs. WRX rotor dimensions (the lip size seems the same). (But I guess anything is possible)
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Last edited by REX8; 05-21-2007 at 06:07 PM.
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Old 05-21-2007, 07:40 PM   #2
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Ok, I'll start:

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Old 05-21-2007, 08:49 PM   #3
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news to me of this being common as I have racing brake h6 kit
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Old 05-21-2007, 08:54 PM   #4
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Semi-common. A number of threads on it that have died with no answer and the Subaru techs saying they are instructed to grind the lip.

Again, I'm not thinking its an H6 issue. Just can't figure out why it woudl all of the sudden be an issue with some people's cars. (again, not a bearing/hub problem either)
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Old 05-21-2007, 08:58 PM   #5
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I had a similar issue when i swapped in rear 2 pots, but ended up bending that lip as I was breaking the dust shield off. I ground it off and the noise went away.

Tony
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Old 05-22-2007, 07:38 AM   #6
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I think this issue is isolated to colder climates where you have snow (salted roads) or regular wet weather. The build up of corrosion on the inner face is greater in these climates which as you suggested is rubbing on the backing plate. The rear groove and backing plate lip is designed seal off the handbrake bore from the elements. Yes the groove is the same dimensions on these discs.

My suggestion would be to spray paint this inner face around the rear groove to reduce corrosion build up. Make a simple carboard mask to protect the rotor braking face from being coated in paint.
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Old 05-22-2007, 12:10 PM   #7
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Quote:
Originally Posted by DBAsteve View Post
I think this issue is isolated to colder climates where you have snow (salted roads) or regular wet weather. The build up of corrosion on the inner face is greater in these climates which as you suggested is rubbing on the backing plate. The rear groove and backing plate lip is designed seal off the handbrake bore from the elements. Yes the groove is the same dimensions on these discs.

My suggestion would be to spray paint this inner face around the rear groove to reduce corrosion build up. Make a simple carboard mask to protect the rotor braking face from being coated in paint.
Thats what I first thought...but..

Problem is, it happens on brand new discs as well, with no buildup on the backing plate what-so-ever. The amount of material that must be removed is also too much to be rust, etc. as well.

I mean, you'd have to think a weak bearing, or bent hub, but I've replaced them on both sides and have been left with teh same results.

Assumings its not a difference in rotor dimensions, what part of the system would change to have that resulting tolerance difference?
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Old 05-22-2007, 12:32 PM   #8
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I'd put money on a tolerance stack-up among a slew of parts...bearing and brake components. So you'd have parts that are all within spec, but several parts to the high/low end of spec. That could be enough to create a rub.

In building anything with a lot of parts, this is common and really frustrating for engineers and mechanics alike...and the solution is usually either "swap parts until it quits" or "machine to fit"

I know that doesn't help solve it, but could be an answer to the "why" question.

-Mike
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Old 05-26-2007, 05:33 AM   #9
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Do you have a pic showing the actual rub marks on the disc?
Assuming it is rubbing in the groove or lip on the inner face.

I'm curious as to whether it is the diameter of the lip on the inner face or the depth of the groove.


Last edited by DBAsteve; 05-26-2007 at 05:45 AM. Reason: add image
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Old 05-26-2007, 07:37 PM   #10
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interesting


<--- small pancake on head
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Old 05-27-2007, 02:26 AM   #11
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I'm not sure if I have a pancake on my head or not. Does that mean I'm waffling?

I know, I know, that was a waffle pun...

Seriously though, I'd like to know the real answer to this one too.
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Old 05-27-2007, 09:06 PM   #12
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I think I've got this issue. Can anyone specify the symptoms? There is a thumpings that increases and decreases with speed on my right rear wheel. Today, it turned into a loud screeching until I slowed down and pulled over. Then no noise except thumping again. Wheel should be balanced. No play in wheel when jacked up. No screeching since.
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Old 07-28-2007, 05:00 PM   #13
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Thanks for posting this, using as a reference! I have gone about three months now and just got rid of the problem by using your reference here! Thanks!
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Old 07-28-2007, 06:34 PM   #14
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i had the same issue, thoght it was just me, never even thought of looking to see if anyone else did...
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Old 10-27-2007, 01:09 PM   #15
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bump got this problem any ideas?
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Old 10-27-2007, 06:13 PM   #16
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...I had the 'h6' rears on my '02 and, of course, the stock brakes and never had this issue.....but I did completely remove the rear dustshields when I did the 'h6'....and I used the dba 657S rear rotors
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Old 10-28-2007, 01:39 PM   #17
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so u think i should remove the whole dust shield how hard was it ill search
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Old 10-29-2007, 06:43 AM   #18
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Quote:
Originally Posted by REX8 View Post
Problem is, it happens on brand new discs as well, with no buildup on the backing plate what-so-ever. The amount of material that must be removed is also too much to be rust, etc. as well.
I put on a new set of OE-size Brembo blank rotors in August and immediately experienced the grind while cornering. A quick trip to the machine shop fixed it. My wheel bearings are (knock on wood) fine. Pretty sure it's "just one of those things..."

BTW-- If you drive in an area where salt is used on the roads, removing the rear dustshields is a sure-fire way to kill your parking brake.
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Old 10-29-2007, 07:40 AM   #19
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I have this problem too... Turning left only at 25 mph or so, from rear rotors. Sounds like a wheel bearing. I went in last year to my mechanic and he said something to the effect of "Theres a bunch of road crud and rust behind the rotor. I spent 30 minuts grinding them down and cleaning it out."

Six months later, it came back, but I haven't had time to get it fixed again. I've only found a few references to this problem, but every time someone posts it, the response is "wheel-bearing".

Stock 2002 WRX wagon, original rear rotors with 50K on them. Had the noise at 40K, replaced pads and removed the crud, back at 46K. I've been tempted to replace the rotors just to get rid of the noise, but it sounds like that may not do it.

Last edited by bg23516; 10-29-2007 at 07:43 AM. Reason: Added the last part.
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Old 10-29-2007, 02:29 PM   #20
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I have this same problem on my car. It happened when the rotors(racing brake) were new only on one side of the car. I fixed it by bending the backing plate some. Then it came back but on both sides of the car about 10,000 miles later. I fugured it was the rotors I was using just had a little to much material and or wheels bearings are getting worn or both. It makes a noise only when turning and you can hear it better at low speeds don't really hear it at higher speeds. I didn't drive my car last winter so it was corrosion.
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Old 10-30-2007, 08:12 AM   #21
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Just curious...if ButtDyno or DrSeuss get on here but, was this the cause of the horrible noise DrSeuss's Wagon was making at the last CDC autox?
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Old 10-30-2007, 02:30 PM   #22
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My car had this noise stock, and it remained after installing H6 rotors after bending the dust shield out of the way. Had it addressed at the dealership I work at and it returned after 2 months. I'd prefer the car not having bonus noises, but have adapted to it being there.
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Old 12-24-2007, 03:04 AM   #23
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Im having a similar problem on my stock 04 STI. I get a shuddering from the right rear only when starting from a complete stop going from maybe 0-10mph. If I start from a stop accelerating slowly I can hear a slight shudder. If I accelerate hard it shudders loudly followed by a thump and then it theres no other noise regardless of speed until I stop and have to start moving again. I did grind the dust cover, but I dont think that its the problem. I presume there would be some scoring on the disc if it were rubbing somewhere. Anyone have a similar problem or a suggestion on something else to look for or try? The bearings seem fine (no play)

Last edited by pilotstephen; 12-24-2007 at 12:44 PM.
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Old 12-24-2007, 09:02 AM   #24
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Quote:
Originally Posted by pilotstephen View Post
Im having a similar problem on my stock 04 STI. I get a shuddering from the right rear only when starting from a complete stop going from maybe 0-10mph. If I start from a stop accelerating slowly I can hear a slight shudder. If I accelerate hard it shudders loudly followed by a thump and then it theres no other noise regardless of speed until I stop and have to start moving again. I did grind the dust cover, but I dont think that its the problem. I presume there would be some scoring on the disc if it were rubbing somewhere. Anyone have a similar problem or a suggestion one something else to look for or try? The bearings seem fine (no play)
I don't think that's a backing plate problem. That's either a dying rear diff or a dying CV.
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Old 03-12-2008, 12:01 PM   #25
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Same grinding noise for me. Found that the dust shield was rusting at the bottom, thus pushing the backing plate out far enough to make contact with the groove in the rotor (only in turns). OP's fix was the same thing we did to correct it.

Anyone know how to replace the backing plate?
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