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?
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.
- 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
- Experience: A dozen or so track days, and 5 open pit lane tracks days in this car.
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
Hard vibration under braking
Audi RS3 8p Brake Problems
Brake problems! read this
Thanks in advance for any input on this to help me work out what's going on.