JayinToronto

Tracked my car hard on Friday. 30min sessions totalling 3 1/2 hours at Mosport (high speed track). Had to replace tires the next morning for the UCR-PCA event and also noticed the breaks getting pretty soft. Though there was definitely wear in the back pads I didn't think they were low enough to give me such a squishy break feel so bled the break lines at the calipers and suctioned out as much fluid as I could out of the reservoir and topped things up with new break fluid. Still squishy, so I changed the break pads. Obviously couldn't get OEM pads at the track on a Saturday but was able to get my hands on a set of Pagid yellow pads and put those on (had to remove the vibration dampers to get them on the rears). Breaks felt much better. Did my first DE session breaking them in at the advice of some of the more seasoned track guys (brought the breaks and tires up to temp with 2 easy laps then hammered on them for a lap then did another full lap without breaking to cool them down). Rest of the session felt great. The next session once I got my breaks and tires up to temp noticed a bit of a vibration coming from the left front corner of my car at hard breaking (230-140km/h). Felt it a little bit at subsequent breaking zones so pitted and checked for debree or anthing obvious with the new breaks couldn't find anything so bailed on the rest of the session. Some people thought that the Pagid Yellows just needed to be broken in a bit more so I went back out for the next session. Felt fine for the first few laps but was stuck in some traffic. Once up to temp and after a few passes I got to hammer on them again and had the vibration come back, didn't seem to be effecting stopping distance so kept going for a bit. Now I noticed that the vibration coming from the left front corner was getting worse with breaking but now it was also there when I was hard cornering under gentle throttle to the right. Things felt fine turning to the left. Things only got worse through the next few corners in both breaking AND cornering so I again pitted. You could both feel AND hear the vibration on the last few corners. Tried to reproduce it on the street to one of my mechanic buddies but at normal temps everything felt normal in both breaking and slalom.

Currently the differential diagnosis includes:

Warped rotor or some problem with the new pads (though not reproducible at lower speeds and also noted on cornering with NO breaking).

Wheel bearing (though not sure why would only be there at high speeds and irreproducible with normal operation, plus the car only has 30k kms on it)

Something in the suspension that's only evident once the wheels and tires are at temperature putting high forces on it.

I'm taking it to the shop on Thursday. Is there anything else I should consider or look at before I take it in. I much prefer to go to the shop with a diagnosis and bargain over the remedy vs putting everything in their hands.

Any and all advise is greatly appreciated!!!

(sorry about the super long post)

AudiOn19s

The odd part is that the symptoms go away when cold. Do you think they really go away or you just can't detect them as well at lower speeds?

Could be wheels weights fell off and the new tires aren't in balance any longer.
Could be warped rotor...always make sure to take a full cool down lap using little to no brakes in order to keep the brakes happy
Could be pad buildup on the rotors. Some race pads can leave deposits on the rotors that give symptoms as you are describing but with pad deposits the harder you use the brakes the more likely the deposits are to go away not the other way around. Also you'd be really hard pressed to feel pad deposits in a turn.

Def. weird, report back what the shop finds.

Igooz

Sounds like a rotor to me...my encyclopedia of worthless track information has aged but that is a track pad and may have chewed up your rotor? IMO

eurotom

Sound like warped rotor or judder from improper bed in procedure.

What fluid are you running your pedal should not get limp.

Tom@TPC Racing

Agreed.

Tom@TPC Racing

It doesn't take much to boil standard grade brake fluid on track especially with stock pads, and especially on a turbo car which the PSM engages the brakes during corner exit throttle without the driver knowing. This occurs even with PSM "off". Track pads will help by transferring less heat to the fluid. Fluid with higher boiling point is a must for track use. Other solutions are to drive smoother, and/or get sticker tires to increase grip for less PSM intervention, and/or upgrade the suspension for more grip. Its a slippery slop but fun.

TT Surgeon

The first time I ever went to lamerock in my old 996c4s I had to have instructor to sign me off solo, some ancient guy kept telling me to" slow down, slow down!!!"
In the pits, my "ck brake pads" light was going crazy, my oem fluid had boiled and actually melted all the sensor wires, psm in an awd Porsche for ya!
I temp brake fluid is mandatory.
OP, I think your brake fluid is toast, when it gets up to temp all its viscosity is gone, abs starts stepping in, etc I doubt your rotors are warped, it's not a 993 that's been sitting for months after all.....
start with some good hi temp brake fluid with a total system flush.

eurotom

^ Definitely agree with the brake fluid regardless of the root cause.

I'm still concerned about bedding procedure the OP went through, Pagid has specific instructions as most other pad MFG's do. Even if this is not the root cause it should be followed.

As another member stated it could be as simple as wheel counterbalance weights falling off due to heat. If so buy some aluminum foil along with new rotors

JayinToronto

Great info guys. Makes sense it would still be slightly present in the corners if the PSM was kicking in. Lord knows I'm far from perfect in the corners. I will get the rotor checked, flush the break fluid and add race fluid. Should I go back to OEM breaks and rotors or keep the Pagid yellows and upgrade my rotors? If yes to pads and rotors any recommendations? I still want to keep my car somewhat civilized for my daily commute. I'm also trying to not do too many upgrades too quickly until I can drive well enough to appreciate the change but it sounds like a pad/rotor/fluid upgrade is essential to my cars (and my) survival.

JayinToronto

Found this on their website. Not what I did. It was a Porsche mechanic with a son who races a GT3 cup car that gave me my instructions. Hope I didn't f&*k things up doing it the other way. The hard lessons you learn as a newbe.....

Guidance On Bedding In Procedure
Geometric Alignment Of Pad Surface To Disc Surface (basic bedding in)
4-6 brake applications with medium pedal pressure from approx 90mph to 50mph, not allowing wheels to lock. (No brake dragging)
Allow for a distance of 300 - 400metres between brake applications for cooling period.
Pads should not reach temperatures above 400°C during initial bedding in. Check that pad
surfaces have at least 80% contact with disc before allowing more heat into pad surface.

Immediately followed by :
Bedding In At High Speed1 brake application with medium to high pedal pressure from approx 110mph to 50mph
without allowing wheels to lock.
Allow 3-4 recovery brake applications with light pedal pressure.
Repeat high speed applications including recovery applications another 2-3 times.
Allow a cooling off distance of 500 metres between high speed applications.

eurotom

I would recommend upgrading your fluid and sticking with OEM Rotors and Pads. Again this depends on how many DE's you plan on running a season.

Re Bedding in procedures- that is a simple one you should see Brembos Rotor procedure, nearly impossible without having a private runway nonetheless I follow it step by step

TT Surgeon

In my blue 997tt I did 125 track days+ with oem pads and rotors with hi temp fluid.

speed21

Agree totally. Unless you are running slicks and have a full blown track set up (alignment), doing a lot of days I can't see the advantage changing from the OEM set up either.

The hi temp synthetic brake fluid goes without saying. To take a car out with regular fluid is a complete waste of time imo especially if you are serious about pushing some decent times. In fact I've seen manual non turbos with their clutch pedal stuck to the floorboards from not changing the fluid there as well. The fluid is critical. TT has the pentosin set up so that one is different of course...

JayinToronto

Wish I would have known that about the break fluid before! Is there any other "must change" before I head out for my next laps?

speed21

I wouldn't worry about it too much. Plenty have made the mistake. Me included.....and i was told beforehand lol. You soon learn what to take notice of and what not to.