disc skimming

[oldnick]

suffering from a vibration when the brakes have warmed up I am considering having the front discs skimmed on car as they look rather tatty rather than worn , so don't want to fit new pads on them

haven't yet got a quote for this but I presume it is cheaper and easier than a couple of new discs at £100 plus

anyone done this ?

ps to conan ...have you go 2 dictionaries in your library , one of which says axle and the other axel ...or are you an ice skater ?

[The_Laird]

Yep, I had that done two or three years ago and it cured a long-running problem with juddering brakes.

I kept getting discs and pads replaced, but after around 1500 miles (IIRC) the juddering would come back, until the on-car skimming cured the problem.

[moltuae]

I've had it done a couple of times (at about £50 per wheel, if I recall correctly). The juddering went away but only temporarily. Came back each time after 1000-2000 miles.

The third time the judder came back, I had the calipers inspected and had the discs and pads changed again, this time insisting on genuine OEM (the previous set were supposed to be genuine, but we couldn't be certain). Also, I decided to (attempt to) properly bed the brakes in this time, though through a lack of suitable safe brake bedding-in locations I may not have done it as thoroughly as a should.

After probably 4000 miles or so some judder has returned but so far it's only very slight. I think I may be causing the problem myself somewhat by holding the brakes on while stationary following some spirited driving/braking. Traffic conditions allowing, I usually try to stay off the brake pedal or keep the car rolling a little while the discs are still hot but of course that's not always practical/possible to do.

[oldnick]

thanks jim , will give it a go then once I have checked the discs are well above the minimum thickness which I believe is 28mm
looking at the service records the car had new jurid discs and pads fitted about 30 k ago , the pads are only about half worn !

what did the skimming cost ? any memory ? I seem to remember that you do a fair mileage so sounds economic if it has already done 2/3 years

[The_Laird]

I can't remember the cost - I'll see if I can find a receipt

[oldnick]

thanks mark as well , you clearly posted as I was answering jim and I didn't see it
strange the difference between your experience and jim's ; have read elsewhere that this is a problem on big powerful cars

I wonder if your idea about keeping your foot on the brake could be the reason , must try slipping it into park when stopping even briefly , mine lurches a bit when I~ do that , always presumed that was normal just like on my landie on the transmission brake

I suppose using the handbrake would be a good idea but it isn't exactly convenient !

[pete-p]

Originally Posted by oldnick

I wonder if your idea about keeping your foot on the brake could be the reason

From what I've read elsewhere this could be the issue. The heat from the discs is causing debris from the pads to be absorbed/stuck to the disc - this is what creates the vibration and why it will come back again.

I guess it's not helped that our cars are automatic so there is a tendency to stop with the footbrake on, other than putting it in park or neutral (with handbrake on) there probably isn't much else to do.

[moltuae]

Originally Posted by pete-p

From what I've read elsewhere this could be the issue. The heat from the discs is causing debris from the pads to be absorbed/stuck to the disc - this is what creates the vibration and why it will come back again.

I guess it's not helped that our cars are automatic so there is a tendency to stop with the footbrake on, other than putting it in park or neutral (with handbrake on) there probably isn't much else to do.

Precisely. That's been my conclusion too from my own findings and what I have read.

Getting out of the habit of holding it on the foot brake, especially when the discs are hot, is the key I think, but sooner or later you're likely to do it again simply because you forgot or it was just unavoidable.

I have often wondered if uprated/vented discs might help.

[MikkiJayne]

Originally Posted by pete-p

The heat from the discs is causing debris from the pads to be absorbed/stuck to the disc - this is what creates the vibration and why it will come back again.

Agreed. Ever since I learned this I haven't had a single problem with brake judder that couldn't be cured by getting the brakes really toasty hot (try a few max-Q 0-60-0 ) and then running around gently to allow them to cool down evenly. The heat and friction cleans up the contamination from the disc surface and then they cool down evenly without picking up any more.

Its force of habit now to knock it in to neutral and pop the handbrake on since I always did that before the S8 anyway. I could get the discs glowing on my A6 on the twisty bits so it was a frequent problem until I learned the solution, and also to not park up while the pads were still smoking

Skimming would solve the problem too of course since it would take away the contaminated surface, but 0-60-0 is cheaper and more fun

[moltuae]

Originally Posted by MikkiJayne

Skimming would solve the problem too of course since it would take away the contaminated surface, but 0-60-0 is cheaper and more fun

Interesting. So you're saying that repeating the bedding-in procedure should actually fix judder caused by uneven brake pad deposits?