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Vibration at high brake pressure, new rotors

turbojzrr

Go Kart Champion
Location
San Francisco Bay Area
Car(s)
'19 Golf R
background:

I had some noise and vibration under heavy braking before using OEM PP brakes + EBC blues. No noise / vibration on light braking, during hard cornering or cruising otherwise. Noise only during heavy heavy braking.

I just installed new macan calipers with new Zimmerman blanks, on brand new Porterfield R4 pads. I thought this would cure the vibration / noise but if anything it seems to have gotten worse.

I ruled out the wheel bearing as when i corner hard there isn’t any noise, and side to side loading the tires also makes no noise. During the new brake bedding process, As i heated up the pads and eventually gave it full load, the vibrations are back and never went away.

Would love to hear what you think might be the cause.
 

jimlloyd40

Autocross Champion
Location
Phoenix
Car(s)
2018 SE DSG
Are you talking about the vibration you would get if the rotors need cleaned off and the steering wheel swivels side to side when you're on the brakes?
 

jimlloyd40

Autocross Champion
Location
Phoenix
Car(s)
2018 SE DSG
Steering wheel gets some vibrations but it isn’t any more than on the body of the car say the shifter or the door habdle
Sounds like the rotors have brake pad deposits that several hard stops from 60 MPH to around 15 MPH would clean them off. Like the brake pad break in process.
 

Bernb6

Go Kart Champion
Location
Palo Alto, CA
Car(s)
2017 GTI Autobahn
Can you see one or more splotches on the rotors? If so that would also be an indicator of uneven pad deposits.
Bern
 

SouthFL_Mk7.5

Autocross Champion
Location
South Florida
Car(s)
2019 GTI S
R4 are dedicated Race / Track day pads that need heat to perform in their operating range. For daily you’re better off with R4S.

Sounds like you need to bed those pads in again. Or, remove rotors, cross sand then bed pads in again.

If this is happening at the track, could be the pads themselves rattling.
 

AceHammer

Go Kart Champion
Location
NY USA
Car(s)
2015 A3
Make sure you never come to a complete stop when re-bedding until the rotors are cool as well. Did that and had to redo it to get rid of deposits.
 

turbojzrr

Go Kart Champion
Location
San Francisco Bay Area
Car(s)
'19 Golf R
Thanks for all the ideas guys. After further analysis I think it might actually be the rear rotors that are warped.

we had rainfall the last few weeks and I had my electronic parking brake set to auto. Before I began work on macan caliper and CS S knuckles install, I had the hand brake on and it was wet. Had the rear brakes tight there a week while doing the front work. I think it might be due to the rear pads rusting onto the rotor. Going to try replacing rear rotors first and report back.
 

jimlloyd40

Autocross Champion
Location
Phoenix
Car(s)
2018 SE DSG
Thanks for all the ideas guys. After further analysis I think it might actually be the rear rotors that are warped.

we had rainfall the last few weeks and I had my electronic parking brake set to auto. Before I began work on macan caliper and CS S knuckles install, I had the hand brake on and it was wet. Had the rear brakes tight there a week while doing the front work. I think it might be due to the rear pads rusting onto the rotor. Going to try replacing rear rotors first and report back.
Were the rear rotors replaced when the pads were?
 

Bernb6

Go Kart Champion
Location
Palo Alto, CA
Car(s)
2017 GTI Autobahn
we had rainfall the last few weeks and I had my electronic parking brake set to auto. Before I began work on macan caliper and CS S knuckles install, I had the hand brake on and it was wet. Had the rear brakes tight there a week while doing the front work. I think it might be due to the rear pads rusting onto the rotor. Going to try replacing rear rotors first and report back.
Rotors rust all the time, after all, it's bare metal. I can't image a few weeks rust with hand brake set would cause a problem. Surface rust would be removed with a few seconds of brakes being applied.
Nonetheless, if you've changed the front pads and rotors and still get braking vibs, it certainly seems like the rears. Is it possible that one of the rotors is not seated flat on the hub? - a little debris under it? Can you see anything different between left and right sides?
 

turbojzrr

Go Kart Champion
Location
San Francisco Bay Area
Car(s)
'19 Golf R
Were the rear rotors replaced when the pads were?
no, still on stock rears everything. They look nearly new and no lip on edge etc...

Rotors rust all the time, after all, it's bare metal. I can't image a few weeks rust with hand brake set would cause a problem. Surface rust would be removed with a few seconds of brakes being applied.
Nonetheless, if you've changed the front pads and rotors and still get braking vibs, it certainly seems like the rears. Is it possible that one of the rotors is not seated flat on the hub? - a little debris under it? Can you see anything different between left and right sides?
That's a great idea as well. I will take it apart to examine! Thanks a lot for the thoughts!
 

jimlloyd40

Autocross Champion
Location
Phoenix
Car(s)
2018 SE DSG
no, still on stock rears everything. They look nearly new and no lip on edge etc...


That's a great idea as well. I will take it apart to examine! Thanks a lot for the thoughts!
I wouldn't have put new pads on old rotors without at least turning the rotors first providing they still could be turned and meet spec.
 

SouthFL_Mk7.5

Autocross Champion
Location
South Florida
Car(s)
2019 GTI S
I wouldn't have put new pads on old rotors without at least turning the rotors first providing they still could be turned and meet spec.
If the rotors don’t have a deep lip there’s no problem with bedding in new pad/compound.. I used to go as far and take the used rotor off and cross sand to prep for the new pads… but a proper bed in is usually enough to transfer a layer of the new stuff on the old rotor.
 

jimlloyd40

Autocross Champion
Location
Phoenix
Car(s)
2018 SE DSG
If the rotors don’t have a deep lip there’s no problem with bedding in new pad/compound.. I used to go as far and take the used rotor off and cross sand to prep for the new pads… but a proper bed in is usually enough to transfer a layer of the new stuff on the old rotor.
Just a thought since he said it was only the rear that was the problem.
 
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