problem after 996 upgrade

[RAOUL]

Hi Peter, be careful of brake test machines at MOT stations, the drivetrain gets loaded up and can cause breakages. It basically "winds" up the drivetrain. You shouldnt put a Quattro on a normal brake tester.

[dan_b]

the pads i am using are standard 996 textar,the system/calipers have been bled fully,everything else is standard.i think i might try and get it on the brake tester at the mot station and see whats going on.

How did you do the system bleeding? How much fluid did you use to bleed each caliper?

Are you sure all the pipes are screwed together properly, no leaks, splits etc?

Are there any leaks around the servo or master cylinder?

[dan_b]

Also, are these new calipers, or 2nd hand? Did you check that all the pistons moved freely?

[HPmuirt]

Hi Peter, be careful of brake test machines at MOT stations, the drivetrain gets loaded up and can cause breakages. It basically "winds" up the drivetrain. You shouldnt put a Quattro on a normal brake tester.

Whilst this is true in theory, in practice at 4MPH for a few seconds it seems that the system can cope, particularly when you think that our cars are between 10 and 25 years old (if you include the few URs that people on here have) and no one has yet to suffer a failure attributed to a 4MPH brake test.

@ Peter: I had my car MOT'd yesterday and scored between 300 and 350 on the front wheels with the 996 monoblock setup using Textar pads (although my pads are shot and about to be changed), so if you do test them, then you should achieve similar values.

Also, you said you ran through the bedding in routine. How do the disks look now? Are they even in colour or showing score lines?

Also, how much did you reduce/grind/press out the pad retaining pins by?

Cheers n

Si

[peter]

thanks for the info si,might be a week before i can get the car on the rollers.
the disks have started to change colour,but to be honest the weather has been so bad its hard to see whats going on.i should be up to 1000 miles by the time i get to the mot so i will let you all know the results.
cheers.

[Jamo]

Whilst this is true in theory, in practice at 4MPH for a few seconds it seems that the system can cope, particularly when you think that our cars are between 10 and 25 years old (if you include the few URs that people on here have) and no one has yet to suffer a failure attributed to a 4MPH brake test.

@ Peter: I had my car MOT'd yesterday and scored between 300 and 350 on the front wheels with the 996 monoblock setup using Textar pads (although my pads are shot and about to be changed), so if you do test them, then you should achieve similar values.

Also, you said you ran through the bedding in routine. How do the disks look now? Are they even in colour or showing score lines?

Also, how much did you reduce/grind/press out the pad retaining pins by?

Cheers n

Si

I only take my car to an MOT station that has a skid pan ala Church Road Garage or ones that use the G-meter.

Not worth the risk IMO. I believe there has been one breakage reported on the forum as it's how I can to know about how the situation when I 1st joined the forum.

[HPmuirt]

I only take my car to an MOT station that has a skid pan ala Church Road Garage or ones that use the G-meter.

Not worth the risk IMO. I believe there has been one breakage reported on the forum as it's how I can to know about how the situation when I 1st joined the forum.

I completely understand that point of view and would never argue against it. However, the local steeler MOT's all quattro based cars on the standard brake tester and has done since the introduction on the UR into the UK (when my friend worked there).

The 2 Audi trained mechanics at my friends garage said that they would offer a G meter test but recommend the brake tester as it gives a more accurate picture of the perfomance at each corner and will therefore highlight any brake related issues. I agree with this and so elected to have the brake test, rather than the G meter test.

Finally, what happens when you turn off the ABS and lock the fron wheels whilst driving at 30MPH on snow or other occasions when the wheels are all doing different things beyond the torsen capability? Surely these are far more aggressive to the diffs than a 4MPH brake test?

Cheers n

Si

P.S. I would be interested to know what the experts on here like Audiman think

[curlyks2]

Also NEVER STOP as you will leave a pad imprint on the disk surface - this is a life rule, not just for bedding in sessions - never sit at the lights with your foot on the brakes, if you braked hard and the brakes are hot. The pad imprint will cause brake judder that is often misdiagnosed as warped disks. In truth, it is virtually impossible to warp a modern disk!

Sometimes - like when some **** inexplicably pulls out or stops in front of you - it's nigh on impossible not to slam the brakes on and come to a complete stop, potentially causing a pad imprint.

Is there a solution/fix to the pad imprint problem that doesn't involve new disks?

Ck.

[Crawford_S2]

Sometimes - like when some **** inexplicably pulls out or stops in front of you - it's nigh on impossible not to slam the brakes on and come to a complete stop, potentially causing a pad imprint.

Is there a solution/fix to the pad imprint problem that doesn't involve new disks?

Ck.

Pretty sure this only is a worry if you are prone to getting the brakes hot, by driving your S in a spirited manner say, then when you come to a stop keeping your foot on the brake pedal. If you apply the handbrake at junctions and the like rather than mashing the middle pedal whilst waiting, this pad imprint thing shouldn't happen. As i understand it anyway

[curlyks2]

Pretty sure this only is a worry if you are prone to getting the brakes hot, by driving your S in a spirited manner say,

Guilty as charged - is there any other way to drive an S2?

then when you come to a stop keeping your foot on the brake pedal.

Not guilty - I make a habit of going for the handbrake to hold the car.

However, still wondering if there is a solution or fix if you do manage to get a nice pad imprint on the disk(s) - preferably without shelling out for new disks. I have had this problem before with a particular disk/pad combination after following good bedding in practice which worked fine and well with other disk/pad variations.

Ck.

[newsh]

Is there a solution/fix to the pad imprint problem that doesn't involve new disks?

Ck.

Give them a good rub down with abrasive paper, I've actually used an angle grinder with a soft wheel and sandpaper, you shouldn't use emery or wet and dry as the abrasive gets into the disc. Spin the disc and sand the surface, if you can do it on a lathe all the better, or take them and get them refaced on a surface grinder.

This imprint thing really only happens if the discs are real hot though, do a 20 min session at Castle Combe and sit in the paddock with your foot on the brake and it will happen. A spirited drive round your local back roads may amount to the same thing though. At track days I always park in gear with the brake off. Its a good rule of thumb to try not to sit with your foot on the brake pedal then you get used to the idea and are less likely to do it when the brakes are hot for some reason. Use your last few miles as a slow down lap to let things cool down with the air going across them.

[curlyks2]

Give them a good rub down with abrasive paper [...]

At track days I always park in gear with the brake off. Its a good rule of thumb to try not to sit with your foot on the brake pedal then you get used to the idea and are less likely to do it when the brakes are hot for some reason. Use your last few miles as a slow down lap to let things cool down with the air going across them.

Thank you - and totally agree.

I've done 20+ minute sessions at Goodwood and others with the track pads in with no problem at all, using the last lap to cruise round using no brakes and allowing them to cool down, and parking with the car in gear and a brick behind a tyre. No warping, no imprints, fantastic time.

Think I had a duff set of (road) pads (no longer in use) though which left an imprint really easy, so I have a pair of discs in the garage with a nice set of imprints which I would like to use again after appropriate treatment. It's gotta be cheaper than replacing the things.

Ck.

[dan_b]

Newsh's solution is spot on. Not sure this is helping the original thread topic though - any feedback?

[HPmuirt]

Newsh's solution is spot on. Not sure this is helping the original thread topic though - any feedback?

To a point. The problem is that this now leaves a very green disk, so you need to run through the bedding in procedure again to recoat the disk with pad material and put a full heat cycle through the disk.

Normal road imprinting is normally so minor that unless you have been on a good 'est drive' and then sit on the brakes, normal driving will remove any disk imprints and the vibration felt should be minimal. In fact a bedding in session or another 'test drive' will normally sort it :mischeif:

As for Peter, well I guess we are waiting for an update, as he could not brake test in the awful weather we had. Now we have had a dry week, we need to see what the bedding in did, what colour the disk are and whether the pad is making full contact now. If so, then I would suggest a re-bleed, preferrably with ATE racing blue to that you can see the colour change of the new fluid coming through. Then next time use ATE racing orange (same stuff, different colour).

If that fails to cure it, then we needto look at the core components, such as the calipers....Have the pins been ground/pressed back, are the pistons moving freely etc.

Cheers n

Si

[peter]

sorry it's been a while,work and more work
ok-the brakes have improved,done about 2000 miles,the disks are a blueish colour now with some fine lines,still not great though they seem to get better if i have to do some long/hard braking ie going down hill but then go off as they cool down.i did bleed the system untill new fluid appeared and the pins were ground down 1mm.
do you think the pads could have been contaminated from the start?from the moment i rolled out of the shed it was p*****g with rain,could it be worth trying another set of pads.
cheers.