I went to a simple organised event on a fast canyon road. Stayed on street tyres. Pirelli P Zero’ Rosso - newish. Also, newish brake discs as well (8K miles on them). Brakes superb but on my third application (coming from 120mph to 60mph) I got a slight vibration through the steering wheel only (no pedal vibration). Few braking applications later it got worse. Then after a fast no braking section of the road on next 2 applications I got no vibration only to return on the next application again.

So this vibration comes and goes!

On the way back home I tried hard braking on the motorway and I’ve had no vibration on three attempts. On fourth it manifested this time only slightly again.

Tyres or brakes? Am I overheating the brakes? Warped rotor would surely vibrate all the time? Is it possible that tyres would flat spot only to return to normal 500 metres? I don’t recall this on Michelins PS2’s.

Anyone has this?

 

only thing occurs to me is rotors nd brake pads need to bed in so if you're confident thats been done. can't help. a warped rotor would surely cause wobble but probably also some squeal under braking or some undue noticeable "rubbing" under conditions that applied the most weight/stress to that one side. thats all i've got. GL w it.

 

what pads are you running? new? ...kinda sounds like a material transfer issue
could also be a worn bushing or link, certain/varying circumstances can reveal issues

 

I am running newish (8k miles) front discs and pads. OEM. Rear just new OEM pads as discs were still ok. What I don't get is why is my problem intermittent? Surely any defect in material would be on first application unless it's heat related?

 

Canyon driving has probably effected a bedding in process.

Uneven material deposition can occur in at least several scenarios. One is prior to bedding in the brakes are used to bring the car down from high speed and the hot pads left in contact with the rotors.

In a variation of the above, and one I experienced with my VW Golf TDi, the brakes are used to emergency stop the car from high speed with rusty rotors. I had washed the car the day before and not driven the car afterwards to dry the brakes. The next AM on the way to work I had to make an emergency stop from highway speed on cold brakes that I had not used since leaving the driveway of the house.

After this emergency stop upon light application of the brakes I could feel a mlld pulsing. I had properly bedded in the new brakes prior to this but I tried another bedding in process which didn't help.

The cure was to either have the rotors machined or replaced. Since the pulsing was very mild and my style of driving doesn't have me applying the brakes lightly except in very rare cases I continued to drive the car.

I had pretty much forgotten about this pulsing thing until at around 140K miles when I was selling the car and the woman who ended up buying the car was test driving it and her braking style brought out the pulsing.

All of the above to lead up to this: It is unlikely uneven material deposition is at the root cause of what you are experiencing.

I find it hard to believe the rotors could warp when hot yet lose this warpage when cold again.

Most likely I think the problem lies with old brake fluid. The braking system needs to be properly flushed and bled to replace the old fluid with fresh.

 

I think your problem is intermittent because your brake pads and rotors are not fully and uniformly heated up. The stock OE brake are made to work great first thing out of the driveway, also in heavy freeway traffic as well as long steep curvy down grades. It may be normal to experience what you did as your brakes heat up and cool down, then heat up again.

Your driving was not characteristic of what is seen as normal day to day driving and consequently you experienced some inconsistencies. These can be addressed by checking rotor laterial runout and resurfacing if necessary and also picking a pad that is more sport oriented. A race pad may be noisy, very expensive and may not work well at other than at elevated temperatures.

Unless you plan to do this very often, I'd live with it.

 

do you(or any close friends) have any other brand/material pads?
If you can install some aggressive track pads it may help clear up a material transfer film

 

Thanks guys. Rotors are one posibility. But wouldn't rotor vibration be felt in a brake pedal itself? If my car sits in a garage for few days (especially as weather turns colder) my Pirellis flat spot and for the first 10 miles I have a similar shimmy on the steering wheel which then clears. My thinking is, that perhaps tyres deform slightly after few hard braking applications only to clear after acceleration making them good again - and round and round we go? Sounds plausible or not?

 

Highly doubt it is tires. Brake discs are possible but actual 'warping' is pretty rare, pad material transfer isn't(and I'm pretty sure this is your issue)...I'd pull the discs off the car and have a good look at them; inspect for hot spots or dull areas...check to make sure caliper pistons are free moving and not stuck(possible cause of your issue).

 

agree with all of the above and have said as much in the other thread. check for improperly bedded pads/terribly uneven alignment(?!?) or even a caliper hanging up. ( funky piston?, but doubtful ). i think this is a "one wheel" issue you're dealing with. but not a tire.

when was the last time you had it in the air for alignment??

 

Thanks guys. Will check out your suggestions and report back.

 

I would say you were simply overheating the street pads. It has happened to me before on another car and it happens when the pads are starting to breakdown from too much heat.

It sounds like you need to run a much higher temp pad (track pad), for that type of usage. Unfortunately you can get into issues with vibration changing from one compound to another (as the old pad material is impregnated in the rotor).

On my M3, which I use as a daily driver and track toy, I run the Hawk HPS for the street and Hawk HT10 for the track. The HPS has almost zero brake dust, is easy on rotors and is quiet. Though this is definitely a pad that is not suited for a canyon run. The HP10 will handle up to 1,300 degrees and is a nice budget option for the track. The best thing is these pad materials are compatible and never give me an issue with vibration switching from one to the other.

Later, Steve

 

Hey Steve,
I'll agree and disagree with your comment; if running factory stock pads I don't think he is overheating/green fading them(unless there is a sticking caliper(s)), they are good pads stock, but I will agree that there are deposits being left on the discs and causing vibration, either from a bad caliper or hard running then sitting on brakes while stopped.
Cheers,

 

Yeah I think you are right, I don't think my braking style changed that much from aggressive to super aggressive lately. And look mate, I don't sit on brakes while stopped thank you very much.

Will check for deposits, heat spots and such...

 

I was also told by my tech I take my discs to a workshop which heat cures them. WTF? Heats them up to huge temp and then gradually lowers the temps waiting at certain intervals for 10-15 minutes. He swears that this will fix it. Have you or anyone heard of this?