Disc skimming

[Hollowpockets]

Hi all, need to get the discs on the noble skimmed on the car after a couple heavy track days at the ring and spa.

Does anyone know of a place who can do this with the discs still on the hubs?

Cheers

Graham

[craig2003]

I used Andy Horne's Precision engineering in Inverness, not sure if he can do them on the hubs but I would suspect so

[Hollowpockets]

Thanks I'll get in touch with him.

[foz01]

Skimming is a false economy IMO, are they two piece aluminium belled ones?

If they are genuinely warped (although warping a disc is very rare) I would be binning them, more likely pad deposits..

[Hollowpockets]

Not if the discs are £300 a piece grooved AP items that have just been fitted!

They need skimmed after the first heat cycle to be true on the hubs (no point skimming off the car really) then will be fine,

this is from AP and the guys who race on them...

[Laplace]

foz01 said:

If they are genuinely warped (although warping a disc is very rare) I would be binning them, more likely pad deposits..

Sorry for being O/T.

This has always been the way I've seen it since reading this article and others some years ago.

[slipstream 1985]

maybe you shouldn't be doing 190mph -0 stops eh?

Edited by slipstream 1985 on Friday 6th April 18:30

[foz01]

Hollowpockets said:

Not if the discs are £300 a piece grooved AP items that have just been fitted!

They need skimmed after the first heat cycle to be true on the hubs (no point skimming off the car really) then will be fine,

this is from AP and the guys who race on them...

Never heard that before, what pads were you using?

300 quid a side, nothing in the scheme of things, my wee raft is about 400 the pair, tiny 295mm all round!

[craig2003]

I skimmed mine due to the other half using the car a lot more than I, the pads were a bit too aggressive for a passive driver and quite a build up of rust was found on the inside of both front discs around half way through their first set of pads. I changed pads after skimming obviously but the same thing has reoccurred. Another set of pads and discs required, although the disc manufacturer has agreed to take the originals back for metallurgy checks after questioning as to their integrity. I will let you all know as to the outcome when I get home

[M20ERT]

craig2003 said:

I used Andy Horne's Precision engineering in Inverness, not sure if he can do them on the hubs but I would suspect so

If its any help theres also a precision engineering in Elgin to save travelling / postage to Inverness

Theres also Phillips Engineering aswell although not sure if they have much involvement with cars / motorsport

[disco!!!!]

M&M auto repairs in Inverness have just got a machine in to do it
It's a disc off job though

[jith]

Laplace said:

foz01 said:

If they are genuinely warped (although warping a disc is very rare) I would be binning them, more likely pad deposits..

Sorry for being O/T.

This has always been the way I've seen it since reading this article and others some years ago.

That article is desperately misleading. The writer claims that he has never seen a warped disc. This is probably because his experience appears to be primarily on race cars.

The test for a warped disc is simple. A dial gauge is set up on the caliper assembly and runs on the surface of the disc. When the disc is revolved any runout will show on the dial. If there is a run out, either the disc or the hub is warped. The disc is then removed and the hub tested to eliminate one or the other. Warped hubs are rare, although I have found them on early Audis and VWs.

The early XJS Jaguars had serious problems with warped discs. I have seen them only last 10k and would throw the dial on the gauge round twice!! Jaguar had to recall many of these cars and finally changed the steel content to cure the problem.

When I serviced the Rover 827 police cars we could not stop the discs from warping. Some of the cars were only 3 weeks old! They simply weren't up to the job. The cure was to fit a set of Brembos.

Only last year I was made aware of problems with discs warping on the 7 Series BMW. I had one in for a service with a set of front discs that had been replaced by BMW only 2000 miles previously. They were spotless; no pad material build up or corrosion. The car was almost undrivable the brake vibration was so bad. I then found out this was the 3rd set of discs fitted by BMW! They clearly have a production issue with these.

Under test they were seriously warped. I fitted a set of high quality after-market discs and the problem is now permanently solved.

OP, I would be seriously miffed if I paid 300 quid for a disc and then had to skim it on the hub after preliminary use. I think that's nonsense and you should question it. If the manufacturer is claiming that it has to be skimmed on the hub, that implies that the hub is out of true. Why would it be?

If the hub is true, and the disc is properly manufactured and running true there would be absolutely no need to re-machine it on the hub: think about it.

J

[F3RNANDO]

jith said:

If the hub is true, and the disc is properly manufactured and running true there would be absolutely no need to re-machine it on the hub: think about it.

J

I'd be interested in the explanation - I've never heard of skimming on the hub - always assumed you had to remove the disc to machine the faces and redrill the holes to clean out old pad deposits.

[craig2003]

EBC offer the same advice of having it skimmed to the hub

[Hollowpockets]

the nobles are known for having poor quality hubs and my one had bad vibrations so i replaced all wheel bearings and hubs with ford items, then put new grooved discs and paged rs29 pads. it was perfect on road but once id done some fast laps at spa it started to wobble, its not only my car but 3 other nobles there with the same set up were getting the wobble and brake fade after 6-7 laps, i once managed 10 consecutive laps before the pedal went to the floor.

one of the guys there with a noble races a bmw m3 and he went through several sets of discs until he got them skimmed on the hubs and they've been fine since.

[Hollowpockets]

jith said:

If the hub is true, and the disc is properly manufactured and running true there would be absolutely no need to re-machine it on the hub: think about it.

J

im assuming the new wheel bearings, hubs and discs in january were all true but since having that initial heat cycle they have gone slightly out and skimming will sort that, no disc is sold having gone through a proper heat cycle on track conditions, my theory is once skimmed and true the same heat won't cause the steels form to change again. I'm sure as hell not binning them after every track day, also looking into getting cooling ducts made up to help things.

[kevbridgend]

We skim all discs on the hubs with a geometric skimmer to ensure a true cut the only discs that
Don't overly like this are drilled discs as they snag on the cutter

[Hollowpockets]

kevbridgend said:

We skim all discs on the hubs with a geometric skimmer to ensure a true cut the only discs that
Don't overly like this are drilled discs as they snag on the cutter

Perfect, ill be in touch soon.

graham

[F3RNANDO]

kevbridgend said:

are drilled discs as they snag on the cutter

Possibly explains my question.

[jith]

kevbridgend said:

We skim all discs on the hubs with a geometric skimmer to ensure a true cut the only discs that
Don't overly like this are drilled discs as they snag on the cutter

Original discs are not faced with a cutter; they are ground with a fine, high speed stone.

I used to have a surface grinder with an electro-magnetic table. I clamped the discs on the wheel face after checking it was absolutely parallel to the hub face and then skimmed them with the stone. The discs were then inverted and clamped on the newly skimmed face and the outer face skimmed.

This made them spot on and with a really nice finish to take the pads. This method presented no problems with drilled discs.

J