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Discussion Starter · #1 ·
Question for the group.

Today on track I was getting an excessive amount of vibration from the wheels under heavy braking. Not every corner, but the hardest braking zones for sure. Even happened a bit on the street. Brakes felt fine with no fade, good pedal, and the car still had the shortest stopping distance of the grid, although longer than normal. It almost felt like ABS kicking in intrusively, although I do not believe that was the case. I could not identify it as coming from any particular corner of the car, and there did not seem to be any un-evenness in the braking.

Tarox rotors and Tarox Corsa pads all around.
Steel brake lines.
Castrol SRF fluid, changed this spring and small amount bled when I did the pad replacement.
Front pads are on their second track day. Rotors were bedded in with a previous set of the same pad this spring. No issues up to today.
Well worn RE-71R tires (debating as to whether to kill them next time or retire them early). These are in pretty rough shape, but I don’t believe they were the cause.
Suspension, etc, unchanged. Same track and configuration that I usually drive.

I just got back, so haven’t pulled wheels to investigate yet.

Thoughts on what to look for?
 

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At what speeds are we talking about? Any vibration through the pedal when you apply the brakes very lightly? The vibration only occurs when you apply the brakes? Warped front discs is the obvious answer but could it be anything else?
 

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My hunch is the suspension and not the brakes, because you should feel it more often if the brakes were the source. Under hard braking, your crossing the strength threshold for something, but not the brakes. I can't be more specific though.
 
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Discussion Starter · #4 ·
At what speeds are we talking about? Any vibration through the pedal when you apply the brakes very lightly? The vibration only occurs when you apply the brakes? Warped front discs is the obvious answer but could it be anything else?
Nothing through the pedal. Sounds and feels like driving over cobblestones - shakes the car. Braking from over 150km/h.
Better if I brake more lightly. Or light then heavy.
 

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Discussion Starter · #5 ·
My hunch is the suspension and not the brakes, because you should feel it more often if the brakes were the source. Under hard braking, your crossing the strength threshold for something, but not the brakes. I can't be more specific though.
Although my gut says brakes, I will keep an open mind when taking thing apart.
Thanks for that.
 

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Look at surface of rotor for any buildup of material especially if it is uneven. Sometimes that happens when you didn't do a gentle brake bedding in with the new pads for a good number of miles before going full hard stop....you mentioned this is a newer set I believe. If that isn't it I would check for suspension related causes. If it is rotor build up I believe the answer is turning the rotors on a lathe to take off the surface a tiny bit....and than doing the gentle brake bedding in again. I think I recall that CallMeAl had a similar issue once....seems he used a wire brush in a drill to take that material off at the track but don't know if that is a good or bad practice.
 

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My hunch is warped brake rotors. Had the same issue with my Z4M. They used to warp for no reason.

Had the brakes skimmed and that fixed it. I had the chance to meet Steve Soper who told me of the importance of doing a cooling lap on tracks and avoiding resting my foot on the brake pedal in red lights, especially if the brakes are hot. Never again had brakes warp following this advice.
 

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When the ABS kicks in for me it feels almost like a ticking/clicking as the wheel rotates. Happens in a regular fashion, maybe every half second or so?

Another option could be pickup on the tyres? I noticed a lot of vibration through the car when I get some pickup but you feel that on the straights etc too so I guess it's probably not that.
 

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Discussion Starter · #10 ·
Thanks for the replies and details, guys.
That's part of what makes this forum so great.

Cool down laps after chequered aren’t offered, but I usually make space behind me and take one when I know that the session is coming to an end. And/or do several orbits of the pits to cool things down evenly and gently. Hoping that is sufficient, but perhaps not. It’s more than most do, though.

I did have an off into wet grass the previous day out (on a cool down lap - thought I was slow enough to make the corner, but did not calculate in the weight transfer from braking required for turn-in, LOL). So that may have caused some warping.

The pads are second time out. So perhaps I did not start them properly. Tarox instructions are for “bedding in” rotors before first use, but I could not find specific instructions for new pads so I did the same as I’ve done with other brands - 40 or 50 progressive decelerations from increasing speeds. If it’s the same procedure as for the first use of the rotors, it involves a few hundred miles of driving before taking it to the track for the first time!!! I’m hopeful that this is the issue, although I’ll have to take all 4 rotors off and get them back on for next Saturday morning. Damn! If you knew my schedule, you’d understand. May need someone to do this for me. Might try some sandpaper first, to identify if there is a built-up area of transfer material on them.

While it’s up on the lift and apart, I will pull, push and rattle every possible joint and put a wrench onto every fastener. The fact that it wasn’t misbehaving on 180Km/hr straights or >1g corners either direction makes me think the suspension is sound though. But another track day with that vibration is bound to loosen something!
 

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This is normal to happen when you brake hard on the race track. I got used to it. On my previous car was really bad - the vibrations where so strong that I literally saw the dashboard vibrations when braking normal. On the alfa is much better - I became so used to this that it feels strange if it doesn't vibrate :)

When braking hard on the race track the pad material impregnates in the discs. After a cooling time (let's say 30 min - 1h) the braking friction is at it's best so the car will brake really well (if you also have grip from the tires). This impregnation is not perfectly uniform so the pads will generate these vibrations.
When you drive on the street the pads are cold so they will wear off this impregnated surface and the vibrations will slowly disappear.

So, you can just drive the car on the street (normal driving) for 1-2 weeks and see what happens. If the vibrations slowly disappear then you find the source without inspecting anything.
 

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Discussion Starter · #12 ·
Cleaned everything up and found no major problems. Sanded down the disks by hand (simply looking for excessive buildup - might have been pointless but it seemed like a good idea at the time).

Went for a test drive with the P-Zeros on ( to rule out tires) and it's still present. It is mostly felt through the steering wheel, but a bit through the brake pedal as well. Harder decelerations from high speed still make the whole car shudder.

Going to try to take it in as I don't have time to disassemble the rotors, have them turned, and put them back myself before next Saturday's event.

Pretty sure it is in front because of the sensation in the steering wheel. If I had to guess, I'd say right front. It spins less freely and tends to stop more abruptly and on the same spot.

Thanks for the ideas, guys!
 

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Discussion Starter · #14 ·
Just realized that I owe you the conclusion.

Took this problem to the dealership, and they concurred that it was uneven pad deposits.

They skimmed the rotors for me, and I carefully built up the braking demands to try and build them up evenly again. Worked brilliantly, and the braking was butter smooth (and reliable) on track today.

@John Elliot this is your solution, I’m certain. Matt from Alfa9 suggested running some very abrasive pads to essentially DIY this process. I don’t own such pads yet, but might pick a set up with next year’s order.
 

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Just realized that I owe you the conclusion.

Took this problem to the dealership, and they concurred that it was uneven pad deposits.

They skimmed the rotors for me, and I carefully built up the braking demands to try and build them up evenly again. Worked brilliantly, and the braking was butter smooth (and reliable) on track today.

@John Elliot this is your solution, I’m certain. Matt from Alfa9 suggested running some very abrasive pads to essentially DIY this process. I don’t own such pads yet, but might pick a set up with next year’s order.
Good you got it sorted. Pad transfer (or pad deposits) as it's called is often the source of the vibrations. Lots of people tend to jump to conclusions and say it's a warp, but 9 out 10 times that's not the case, but simply hot spots on the pads that have transferred and create a vibration in the steering wheel.

Fyi, if you aren't close to a shop who can skim the rotors, you can also hit the rotor with a drill mounted brake hone to remove deposits and refresh the surface.
 

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Just realized that I owe you the conclusion.

Took this problem to the dealership, and they concurred that it was uneven pad deposits.

They skimmed the rotors for me, and I carefully built up the braking demands to try and build them up evenly again. Worked brilliantly, and the braking was butter smooth (and reliable) on track today.

@John Elliot this is your solution, I’m certain. Matt from Alfa9 suggested running some very abrasive pads to essentially DIY this process. I don’t own such pads yet, but might pick a set up with next year’s order.
I have the Tarox rotors and pads on the front, exact same issue on the driver’s side, vibration when braking at speed above 60km. When you said the dealer “skimmed” the rotors, exactly what did they do? Thanks.
 

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Discussion Starter · #18 ·
I have the Tarox rotors and pads on the front, exact same issue on the driver’s side, vibration when braking at speed above 60km. When you said the dealer “skimmed” the rotors, exactly what did they do? Thanks.
They basically turn them on a lathe - I did not see the process in action, but that's my understanding.
The intent is to remove the buildup, but as little of the actual rotor material as possible.


 
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