Jump to content

Photo

Track Day Judder on Moderate Braking (Hard Braking OK)

- - - - - Brake Judder

  • Please log in to reply
3 replies to this topic

#1
Tigger

Tigger

    Member

  • Valued Member
  • PipPip
  • 14 posts

Hi,

 

I had a weird experience on a track day at Silverstone recently with a significant judder coming through the steering wheel when braking moderately into the braking areas which wasn't present when I braked much later and much harder into the same braking areas.

 

I was giving passenger experience rides at an event and doing 3 lap stints (out, fast, in) with a 10 - 15 minute gap in the pits in between to pick up another passenger. Braking in the first few corners on the out lap was OK but as I started to speed up as the tyres came up to temp and I started braking a little harder I got a significant judder through the steering column. I was probably braking at about 75% - 80% of what can be done so the judder was quite unexpected.

 

I did all the usual things. Came back in. Checked the wheel nuts. All torqued to 120nm. Checked the tyre pressures. All good. I was running 40 PSI all round as the tyres weren't going to get that hot given the short stints. Gave the wheels a good pull to check for any movement (e.g. bearings, bushes). All OK. Checked the tyres for damage, bulges. Nothing obvious,

 

So I decided to try braking much later and harder into the corners and surprise, surprise, the judder all but disappeared. I just got the normal (slight) vibration while slowing from 80 mph to 70 mph that a lot of us RS3 owners know about. It wasn't completely gone but the judder didn't really build up to be as significant, probably due to the braking period being much shorter

 

So I did the rest of the sessions braking much later and much harder as I normally would on a track day.

 

So I'm left a but puzzled about what's going on.

  • It can't really be warped discs as I'd expect the judder to get worse the harder I braked, and I expect to really feel that through the brake pedal and I don't. I also didn't get any judder on the way back from the circuit when driving/braking normally, nor when I did some spirited braking as a test (where it was safe to do so).
  • I don't think it's wheel/tyre balance as this set is only used for track days, and they have been Hunter RoadForce balanced by Jackson's Ford in Henley and they've always done a good job in all the years I've had my sets balanced there. Plus the usual slight vibration accelerating through 70-80 is there as normal, as it is when braking down from 80 to 70. All as normal.

 

So I'm left thinking this is something else.

 

  • Could it be the calipers binding, or backing off?
  • Could it be the ABS getting involved when it shouldn't be?
  • Could it be an impending Haldex issue?

 

Track Conditions:

Sub-optimal. The track was drying out but still a little bit greasy/slippery from a very wet morning session. I wasn't feeling any under-rotation from the tyres when breaking moderately, and not expecting any. I was getting some under rotation towards the end of day when I switched to breaking late/hard in line with what I've experienced before when trail braking.

 

Specifications

  • Car: Audi RS3 8P (2011/2012).
  • Engine: Standard 335 BHP. Not modified or chipped.
  • Shocks: Standard Audi OEM. Never been replaced.
  • Springs: Standard Audi OEM. Fronts were replaced a couple of years back.
  • Brake Discs: Standard Audi OEM both front and rear. Front/Rear replaced 6 months ago.
  • Brake Pads: EBC Bluestuff Brake Pads DP52070NDX, EBC Bluestuff Brake Pads DP51518NDX. Installed 6 months ago when the discs were replaced and bedded in according to EBC's instructions.
  • Brake Lines: TAROX Braided Brake Hoses (Audi RS3 (8P), Audi-HOSE-33). Installed 6 months ago when the discs were replaced.
  • Tyres: Michelin Pilot Sport Cup 2. Only their second outing on track. Still lots of tread left.
  • Wheels: Standard rotors (as from the factory).
  • Configuration: 235/35 R19 91Z (Y) XL (on all 4 corners).
  • Sport Mode: On
  • ESP: On (all on).
  • Gears: Manual

Driver

  • Competent/Safe/Cautious/Quick
  • Experience: A dozen or so track days, and 5 open pit lane tracks days in this car.

Posts:

I've read through a number of posts (as below) but thought I'd post the scenario I am seeing where the symptoms are not consistent between light, moderate and hard braking.

 

Brake judder under load
https://www.audirs3o...der-under-load/

Hard vibration under braking
https://www.audirs3o...-under-braking/

Audi RS3 8p Brake Problems
https://www.audirs3o...brake-problems/

Brake problems! read this
https://www.audirs3o...lems-read-this/

 

Thanks in advance for any input on this to help me work out what's going on.



#2
RS3Dell

RS3Dell

    Elite Club Member

  • Valued Member
  • PipPipPipPip
  • 4,808 posts
  • LocationToo close to Roy.

A friend & myself would get vibration/juddering through the steering wheel when braking from very high speed 110/150mph when we started to cook the DS2500s after a few laps at Bedford autodrome,we would then come in let them cool down go out again then after a few laps it would come back,this is the cycle we would do all day.

We both now used PBS Prorace without any issues & ATE200 brake fluid,we both have 8Ps but I have the 8v 8pot set up with Reyland two piece fully float discs on the front with 350mm fixed two piece on the rear my friend has the stock set up.

We both run with the traction control fully turned off so not to cook the brakes Inc in the wet with MPS4s on stock wheels.

Both cars are remapped with high quality adjustable aftermarket suspension.

Dell

#3
Tigger

Tigger

    Member

  • Valued Member
  • PipPip
  • 14 posts
@RS3Dell

Thanks. I must admit I didn't think to switch off the ESP as I thought it best to have a little help with traction due to the vibration and the conditions in general, and it was my first time at Silverstone too.

The car was at least still braking straight as you like even while vibrating. No pulling to the left or right.

I didn't realise that ESP on/on would be a significant factor in heating up the brakes but now I think about it, in the marginal conditions while the track was drying the traction control would have been working overtime. Doh!

I'll go out with ESP off/on or off/off in the future. If that's causing excessively hot brakes then I should at least get a longer stint before they start overheating and causing a vibration.

I did take one passenger out for 5 laps so that was a longer stint. The vibration didn't get progressively worse. It just hit a certain level during the 3rd lap and stayed about the same.

Sent from my SM-G991B using Tapatalk

#4
RS3Dell

RS3Dell

    Elite Club Member

  • Valued Member
  • PipPipPipPip
  • 4,808 posts
  • LocationToo close to Roy.

Tigger

To switch the traction control fully off you hold the ESP button for more than 3secs or until it shows "Warning Restricted stability" it will show "Sports" before hand.

As your running Cup2s traction shouldn't be a problem once warmed up tbh.

I've also removed all the splash guards in a bid to get as much cooling air to the brake discs as possible which hasn't cause any issues on the road.

Dell.




Audi RS3OC Forum is Powered by APR Motorsports UK
© 2013-2014 Audi RS3 Owners Club | All rights reserved | This club and forum is not officially associated with AUDI AG.