2008 Polo GTI 9N3 brakes and brake master Cylinder upgrade - ESP question

[simon k]

Just thought I'd let you know mate that the traction controls' throttle cut was successfully cancelled on my car. So if you don't press the 'ESP' button on the dash (which is really just a traction control on/off button), thereby leaving the traction control in its default on position, there now will be no throttle cut but the EDL brake modulation which is factory active below 40km/h is still active. From what I could glean from the tuner, as far as he could see it was a situation where the throttle cut could only be fully on or fully off. We'd been hoping that it could remain in place but have its influence damped down so that it would actually be functional but not so, so it was removed altogether. His concern with killing off the throttle cut was that in wheel spin conditions the ECU might chuck a wobbly and not seeing the rpm arrested as suddenly as it would like, might jam on the EDL braking even more to get the wheelspin into a window it was happy with. I haven't been able to test it from a standing start but if I give it a bit in second up a hill in the wet I can feel the EDL braking working away to maintain traction (which is exactly what I wanted) , but then once you get above that 40km/h threshold you can feel the braking drops out and if you don't have your right foot in the right spot then the wheelspin will increase again. I'm cool with that considering that I'll be on R spec tyres with a lot more grip when I'm on the track, and in the wet I would not normally be that ham fisted with the throttle - I was just doing that to test it. Who knows it may be worth exploring to see if the EDL brake modulation can have its threshold moved up to say 60km/h which would make it pretty functional for the wet I think. For sure its going to need more testing and definitely I need to see how it reacts from standing starts (which is the whole reason why I wanted it). The idea there was that I might be able to launch with higher rpm so that the car isn't as prone to bogging if you only drop say 500rpm from where you should be when you release the clutch, and also I think that the braking will help keep the torsen diff locked. These diffs need torque running through them for the diff to be able to apportion drive so if the braking can keep a wheel that is tending towards free spin attached, then hopefully the diff will stay more consistently 'locked' and not do that left to right switching as it chases each wheel that lets go in succession like it does with the ESP button off.

that's very interesting Sam - I wonder what speed EDL is *capable* of controlling - IE how much it can be used before it cooks the brakes

It would be handy for my track tune until I can afford a diff, and I'll probably start doing a few motorkhanas with the polo soon - though 40kph is enough for that

[sambb]

yeah I think itll help getting it off the line wet or dry and probably out of really tight hairpins etc. But above that yeah I think you'd be cooking the brakes if you didnt have an LSD. Lots of cars are running EDL these days though inc many many performance cars so I wonder how their threshold compare to our cars.

[pologtiforfun]

So i upgraded the front brakes to 312mm....also tried the rears but had problems with the 256mm discs ( maybe i didnt get the right 256mm calipers or discs that i purchased, and yes i did have the 6mm spacers..Anyway fronts on and rears a working in progress.

As i rebuilt the front the brakes may need time to bed in the new seals as well as new pads......i do have a long pedal at the moment. I did pressure bleed the calipers.....so see how it goes. braking has definitely improved but pedal is now longer.

didnt do the brake master cylinder yet....might wait for the brakes to bed in, and maybe then re-bleed to see if it improves.

if not i guess its back to reviewing the brake master cylinder upgrade

[sambb]

good stuff. well keep us posted re the master cylinder if anything happens on that front. very interested to see what happens there.

[pologtiforfun]

Finally got some time to look over the rear caliper situation and i believe its similar to a thread by rgvlee, rear brake upgrade. I encountered the same issue with the space or gap on the rear brake carrier hitting the brake disc.....so i'm now looking to get the correct rear brake carrier. And then i can upgrade the rear calipers

[pologtiforfun]

I managed to find a 2003 bora in a wrecking yard on my way to work......so now have those rear calipers as well and carriers. Not a bad buy $100 for both of them....bonus was i also got the shims so now the rear brakes also wont rattle or click.

Now to clean them up and give them a coat of red caliper paint.....i will check but i believe i will only have to do the carriers as i think they are the same lucus calipers on the Audi TT as the Bora with 256mm discs...also a big thanks to Gav for helping me with a confirming sms

[sambb]

http://www.vaglinks.com/vaglinks_com...on_Control.pdf

here's a VW paper on its traction control systems.

[pologtiforfun]

Thanks Sam,

I'll have a read over the weekend.........hows the car been since you had the "traction control removed"

[sambb]

I'm pretty sure its quicker froma standing start with it than without despite having an LSD already. I have a hillclimb comng up so I've been doing some practice starts and it definitely is easier to more consistently get the car away using the TCS without the throttle cut. It'll pull away from a stand still straighter rather than do a little slew sideways and its generaly just harder to stuff it up. With the TCS turned off (no EDL) if you are not right in the pocket at 2500rpm when the car is boost loaded against the clutch and handbrake it can more easily bog or conversely light up the tyres. With the TCS you can let the clutch go and have much better traction all through 1st gear basically. In other gears you are never really going slow enough for it to be noticeably useful for anything else, but the track i'll be at on the weekend is incredibly tight so maybe it'll help. Having said all that, once I'm on sticky soft compound R specs I dont know if there'll be enough tyre slip off the line to make the TCS intervention useful. It could be that I'll be able to launch at 3000rpm now though! - just dont know till sunday.

[pologtiforfun]

Sam good to see its made a difference, be keen to hear how the track day went ?

also just read also about the quick shift you put in.....guessing that makes a big difference ?

Got the brake carriers all cleaned up and painted red.....hopefully get the rear calipers and discs sorted next weekend.