Pro-Cut Disc Skimming

[smokin]

Since installing new uprights, hubs and alcon discs to the front I've been concerned about the run-out on the front right disc.
On each rotation when jacked up I could hear the FR disc and pads(s) making contact at one particular point. Under light braking at slow speeds e.g. stop/start traffic or coming up to lights (when not driving like a looney) it felt like I was cadence braking. The LF wasn't as bad but I could still hear a slight drag (at two points) when jacked up and rotated.

So, as these were new discs I considered sending them back until I did some research. Turns out that the tolerances worked to by manufacturers are quite generous and when added together can cause a significant amount of run-out at the disc face. This is where Pro-Cut comes in.

Pro-Cut lathes attach to the hub and skim the disc on the car to within 0.025mm. That’s less than the thickness of a human hair! So I braved the bad weather yesterday and headed to N. Wales (1hr from me) to get mine sorted.

The FR was, as expected, very bad. But, and here's the bit that narks me, it was bad on the outer face and much less so on the inner face. The chaps told me that had it been bad on both it would be a combination of hub and disc tolerances. As it was primarily outer it's just a badly made disc. Given how much we're paying for these alcon discs I was not happy.

Anyway, had the fronts and rears done even though I hadn't noticed the rears being a problem. The rears were, however, quite bad too but understandable as I suspect they are the originals from 8 yrs ago. Since the discs are grooved they have to do outer and inner faces separately, so in all it took 2.5hrs to do all four corners.

I took new pads with me and the guys greased them up with Caratec, fitted new R clips and had me road test - boy what a difference. Once I'd got them warmed up the stopping power was like throwing an anchor out the back (and they're not bedded in yet!), and very smooth at slow speeds.

Total cost £145 and the discs can be skimmed up to 3 times depending on how bad they are. They said I'd get probably one more skim for the front right!

The high performance guys like porsche have this kit in all their dealerships and skim new discs as a matter of course before releasing the vehicle.

I would highly recommend this service. There's a website showing all the service centres with the kit here http://www.skimmydiscs.co.uk/ , this is the lathe http://www.procuteurope.eu/ and these are the guys I used http://www.automark.info/

[Karl V]

Thanks for highlighting this thread on viewtopic.php?f=1&t=16916

This sounds really intriguing. May I ask: 5 years on, what's the experience been?

Have you found everything has worn a bit more evenly since skimming? Is there a chance that the pads have worn slower given (presumably) a more even contact?

The Pro-Cut website claims precision skimming will help with pad squeal too (another common topic on here) - have you noticed any difference?

Cheers Smokin.

Karl.

[smokin]

Hi Karl,

Blimey, has it really been 5 yrs!

From my experience, 10/10 and best £145 spent on the car. Discs and pads are still smooth as a baby's... and one Ceratek coating does me for a whole squeal free year. Can't say I've noticed any slower wear. I've marked the discs and studs so I make sure they go back in the same position as the milling profiles the discs to match the throw of the hubs.

If you're thinking of replacing discs because they're warped, seriously consider the skimming.

No squeal is great but the lack of modulation under the foot when hard on them is the biggest improvement (more noticeable with race boots) - and it's still great today, 5 yrs on.

[Karl V]

Great to know, thanks.

I can't confess to being aware of any brake disc wobble or wear at 4,000 miles in to ownership - I was more interested in brake squeal at this point - but your write up was first class and deserves a <bump> in my opinion.

5 years isn't that long to wait is it?

I'm watching other threads about brake squeal to try and work out a match between precision ground brake discs with chamfered pads.

If I learn anything by 2023, I'll be sure to post