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Old 01-29-2013, 03:06 PM   #1
scoobydoobydo
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2008 STI Stg 2
MY03 RIP

Default Braking Low Speeds (DTV issue?)

Under all speeds when I press the brakes hard, but especially low speeds, I'm getting some serious wobble from the front and through the steering wheel.

Got EBC slotted all around and EBC redstuff (street). Approx 5k miles.

I hit the Break-in point and then I towed a bike and trailer (total weight 1100 lbs) about 900 miles.

I've done this before on stock brakes--no issues. Suddenly I'm having a bad wobble issue.

Herein lies the question; if it was a Disc Thickness Variation (DTV) issue.. Would it be every time I hit the brakes, or just sometimes.

Sometimes, I'll get really bad wobble.. Then other times.. Very subtle.

If it is a DTV issue.. Will having them resurfaced (potentially a couple times) Fix the issue?

Any input would be great.
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Old 01-29-2013, 03:07 PM   #2
scoobydoobydo
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MY03 RIP

Default

'Break-in' point implying... Brake, break-in point. It's an 08 STI with 50k miles.
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Old 01-29-2013, 05:03 PM   #3
HinshawWRX
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POWERTRAIN= motor.

Moved to the correct forum for you....
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Old 01-29-2013, 05:18 PM   #4
scoobydoobydo
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MY03 RIP

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Sorry--still getting used to this app.
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Old 01-29-2013, 07:31 PM   #5
rbaldi
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Originally Posted by scoobydoobydo View Post
Under all speeds when I press the brakes hard, but especially low speeds, I'm getting some serious wobble from the front and through the steering wheel.

Got EBC slotted all around and EBC redstuff (street). Approx 5k miles.

I hit the Break-in point and then I towed a bike and trailer (total weight 1100 lbs) about 900 miles.

I've done this before on stock brakes--no issues. Suddenly I'm having a bad wobble issue.

Herein lies the question; if it was a Disc Thickness Variation (DTV) issue.. Would it be every time I hit the brakes, or just sometimes.

Sometimes, I'll get really bad wobble.. Then other times.. Very subtle.

If it is a DTV issue.. Will having them resurfaced (potentially a couple times) Fix the issue?

Any input would be great.
Yes, it is possible to have bad vibrations through the wheel sometimes and not others due to DTV. Wheel (read: rotor) angular phasing is really important in whether or not the steering wheel torsional vibration mode is excited. Example: the front wheels are phased correctly so that the wheel shakes really bad. Now you go around a corner, and since the outside wheel rotates more than the inside wheel, the wheel phasing has changed - you may get lucky and they are now aligned so that the wheel doesn't shake, or they may still be aligned so that it shakes. Eventually it will probably get bad enough that the steering wheel shakes no matter what.

Yes, resurfacing should help, but make sure that the hub is clean and free from rust/dirt when you install the rotors. Same goes for the rotor itself and the wheel mouting surface. It is possible for a wheel that's not flat to cause rotor lateral runout when it's bolted up.

A major cause of DTV on street cars is casual contact between the rotor and pad when driving down the highway combined with lateral runout of the rotor's friction face, which is probably why you noticed this after a long trip. If the pad only skims the high spot of the rotor, it will wear off the transfer layer and cause DTV. For this reason OEM's have quite strict tolerances on rotor lateral runout when the car leaves the factory. Also, your pads may not be helping - some pads will tend to self-correct - the DTV will oscillate between say 5 and 15 microns, but will never get bigger than that. These pads tend to be more noisy and will wear the rotor more. Other brake pads, I have no data but I'm guessing that EBC Reds may be part of this group, DTV will grow exponentially - once a little gets started it gets out of control quickly. I have seen DTV grow from 5 to 60 microns in just a few miles during testing. These pads tend to be quieter and wear the rotors less. You may find that even if you resurface your rotors, the shake will be back within a few hundred miles or so.

No need to resurface more than once at a time, that's just wasting rotor thickness (money).
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Old 01-30-2013, 03:20 PM   #6
scoobydoobydo
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Quote:
Originally Posted by rbaldi View Post

Yes, it is possible to have bad vibrations through the wheel sometimes and not others due to DTV. Wheel (read: rotor) angular phasing is really important in whether or not the steering wheel torsional vibration mode is excited. Example: the front wheels are phased correctly so that the wheel shakes really bad. Now you go around a corner, and since the outside wheel rotates more than the inside wheel, the wheel phasing has changed - you may get lucky and they are now aligned so that the wheel doesn't shake, or they may still be aligned so that it shakes. Eventually it will probably get bad enough that the steering wheel shakes no matter what.

Yes, resurfacing should help, but make sure that the hub is clean and free from rust/dirt when you install the rotors. Same goes for the rotor itself and the wheel mouting surface. It is possible for a wheel that's not flat to cause rotor lateral runout when it's bolted up.

A major cause of DTV on street cars is casual contact between the rotor and pad when driving down the highway combined with lateral runout of the rotor's friction face, which is probably why you noticed this after a long trip. If the pad only skims the high spot of the rotor, it will wear off the transfer layer and cause DTV. For this reason OEM's have quite strict tolerances on rotor lateral runout when the car leaves the factory. Also, your pads may not be helping - some pads will tend to self-correct - the DTV will oscillate between say 5 and 15 microns, but will never get bigger than that. These pads tend to be more noisy and will wear the rotor more. Other brake pads, I have no data but I'm guessing that EBC Reds may be part of this group, DTV will grow exponentially - once a little gets started it gets out of control quickly. I have seen DTV grow from 5 to 60 microns in just a few miles during testing. These pads tend to be quieter and wear the rotors less. You may find that even if you resurface your rotors, the shake will be back within a few hundred miles or so.

No need to resurface more than once at a time, that's just wasting rotor thickness (money).
Thank you for the info. Sounds like my only real fixes are trial and error fixes or just complete replacement. Lol.
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Old 01-30-2013, 06:55 PM   #7
rbaldi
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Originally Posted by scoobydoobydo View Post
Thank you for the info. Sounds like my only real fixes are trial and error fixes or just complete replacement. Lol.
Yeah, that's the trouble with aftermarket stuff. Brake noise and DTV generation testing takes quite alot of time and money, and most consumers of aftermarket products don't care nearly as much as the typical OEM customer.

It may be worth it to try to measure your lateral rotor runout to see if that is the likely culprit. Just put a dial indicator onto the rotor face and spin the wheel. Make sure to do this with the wheels ON and properly torqued down. If there is more than about .003" of runout, I'd start looking at why that may be the case. Make sure to do it on both sides of the rotor so you can measure the thickness variation too.

If you are looking for a more forgiving pad, look at pads that make alot of dust. Unfortunately, lots of dust is typically the price you pay for a pad that doesn't build up DTV too bad but still has good friction.
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Old 01-30-2013, 08:25 PM   #8
scoobydoobydo
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2008 STI Stg 2
MY03 RIP

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I'm by no means a brake guy, but if I just took it to the track and laid into it, would that fix anything? It would seem to me that if the rotor is seated properly and there's build up on the pad and rotor... Couldn't you just cook it off and get it to become a smooth surfaced?

What other potential damage will continuing to use these rotors do to the vehicle? Any ideas?

I'm definitely not looking for a more forgiving pad, but I've also had multiple variations of slotted/drilled... Street/track, brake rotors and pads on various other vehicles and I've never had an issue like this. Also my car is white.... And i like to keep it that way as long as possible.. No brake dust... Lol

Thanks for the continued support.

Last edited by scoobydoobydo; 01-30-2013 at 08:32 PM.
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Old 01-30-2013, 08:55 PM   #9
rbaldi
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Sorry, meant "more forgiving" in terms of DTV generation, not friction level. Typically pads that don't make alot of dust tend to have DTV issues, but that's just a generalization - there are alot of variables at play here.

As for trying to get rid of the DTV on the car; it may help to get it hot or it might make it worse - depends on what happens to the pad compound at high temperatures. I think you will have to call EBC on that one.
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Old 02-01-2013, 12:28 AM   #10
scoobydoobydo
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Just finally took off the rotors and had them resurfaced at O'reilys. Put them back on and they feel like new. No issues at all... Brakes grab hard and there's no vibration.

But like you say.. It may resurface in a couple hundred miles or so. If that's the case.. I'll repeat this process one last time. If it happens again after that.. I'll just go with wilwood or stop tech. These ebcs aren't living up to their rep so far.
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