Skimming dicsc

[fubar andy]

I'm in a bit of a pickle here...

I need some new discs for my K-Sports, however I've been told by Apex (main stockists for K-Sports) that they won't have any stock for 6-12 weeks!!!!

I've got a trackday coming up in 15th November at Oulton Park with the MLR, they said they could air freight them for mega bucks, but there is no guarantee they will even be here in 4-8 weeks.

I've looked at using alternate discs from AP or Alcon, but they are astronomical in cost.

So as a last resort, I'm thinking of getting them skimmed as a temporary measure so I can attend the trackday and then sort them out afterwards.

Main question is will they last the trackday as I've been told that skimming them will only make them warp the opposite way and judder just as much, or will that take some time to achieve?

Has anyone skimmed discs before and used them hard afterwards with any issues?

Cheers

 

[Makaveli_se7en]

My Ph.D was on brake disc optimisation for convective heat transfer, I worked in collaboration with another researcher that looked at thermal deformation and judder.

One of the things we tried was measuring the disc thickness variation and run out of a new disc, we then baked it on a brake dyno. It was then skimmed and tested again. We found that even under normal loads the skimmed disc continued to deform. The hypothesis was that the disc originally deformed to a point where the surface stress prevented it deforming further. By skimming this work hardened layer was removed allowing the disc to further deform, due to the changes to the grain structure already in place due to the original abuse.

So I would think that if you skim the discs you may get a bit more life out of them but they won't be returned to an as new state.

There was some additional work where my colleague looked at heat treating the used discs but I don't recall the results.

 

[MarkTurbo]

Have you checked the disc run out on the car with a dial test indicator?

If not i'd give it a go as its actually pretty rare to warp a disc and most of the time its either a problem with the hub/wheel bearing or uneven pad deposits. If you haven't been driving the car particularly hard lately I'd go out and do the pad bedding in procedure again as it might sort it out.

What pads are you using? Some pads like DS2500 for example are well known for leaving uneven deposits on the disc. I had a set on my Ap's and started getting bad juddering under braking, as soon as i binned them for XP8's it disappeared straight away ;-)

 

[PobodY]

Would you get enough more life out of them for one more trackday? - It's unfortunate, but the track is probably the one place you will get the discs cooking again; if Ed is right, I'd guess the existing grain boundary just becomes a germination point for further phase change.

I would be interested to find-out if re-tempering the discs achieved anything. - In theory you could reset the morphology, but I have a suspicion you'd also encourage deformation in the process... which would leave you with a disc that needs skimming.
Maybe with the right furnace and conditions?

 

[Jon Olds]

If you get them reskimmed, you need a double sided tool, ie one that can cut both sides of the discs without having to flip it in the chuck.
I'm sure you can work out why..
Jon

 

[fubar andy]

Have you checked the disc run out on the car with a dial test indicator?

If not i'd give it a go as its actually pretty rare to warp a disc and most of the time its either a problem with the hub/wheel bearing or uneven pad deposits. If you haven't been driving the car particularly hard lately I'd go out and do the pad bedding in procedure again as it might sort it out.

What pads are you using? Some pads like DS2500 for example are well known for leaving uneven deposits on the disc. I had a set on my Ap's and started getting bad juddering under braking, as soon as i binned them for XP8's it disappeared straight away ;-)

Interestingly I've been reading more information on "warped discs" and info on the MLR.

You're right about being very difficult to warp discs, so I am more inclined to think it might be some sort of deposit on the discs (albeit I can't see them).
Its been months since I've driven the car in real anger and the last time I did down a section of roads I "test" on that's when the vibrations began (once they were hot).

Currently I think the pads I have are Mintex 1166's, which have just about seen their best, so some XP8's were ordered earlier today.

I'll take the discs off this weekend and give them a clean up with some Iron-X and clean the hubs as that was an area that is sometimes over looked!
Other than that I'll have to wait until Jim and I have finished mapping my car and then I can unleash some heavy breaking and see if that clears it?

Also to note, I've not got a dial test indicator, what is it and how to I use one?

Below some info I read that I found very interesting from Stop Tech.

Stop Tech website

 

[red reading]

I had all the issues you had Andy and mine was pads leaving deposits on the discs, was cured by a good clean up and carbotech xp10 all round....no issues at all now. And a dti is a probe on a dial like a watch, if you push the probe in it measures the distance it moves on the dial, they are a precise way of measuring disc run out and other stuff that moves.

 

[fubar andy]

I had all the issues you had Andy and mine was pads leaving deposits on the discs, was cured by a good clean up and carbotech xp10 all round....no issues at all now. And a dti is a probe on a dial like a watch, if you push the probe in it measures the distance it moves on the dial, they are a precise way of measuring disc run out and other stuff that moves.

I'll give them a clean up and try them out once the car is road worthy.

Hopefully that should sort it out!

 

[R called Jay]

Unfortunately i suffer alot from warping and cracking discs.
Not sure if it's a set-up problem, cooling problem or just bad driving.
Thought i'd found the problem being an old style design (where the bells had a lip on them to locate the rotors, and this in turn restricted the expansion and contraction advantages of a bell and rotor set-up) but have cracked another disc.
Anyway, i've had lots of discs skimmed (as long as still within spec) and they've always been a revelation and pretty much as good as new.
Once skimmed i've not found them any worse than new, but then again i've got underlying issues somewhere.
I've just started using discs from Martin Hadlem at Reyland Motorsport and they are lots cheaper than my previous AP's/Goodspeed/Hi-Spec.
They lasted 2 trackdays so better than normal :-(

 

[fubar andy]

What pads were you using?

 

[R called Jay]

I was using ferodo ds2500 but have moved onto some performance friction ones.

 

[lakeview]

What size discs you using?you tried places like rally design

 

[The Doc]

Have you spoken to a brake pad manufacturer regarding this as it sound like you have deposits being left on the disc which is causing un-even disc temperatures and gassing and then hence warped discs, warping discs is very rare unless there is an issue of overheating which to a degree the pad should be removing the heat from the disc.........do you boil brake fluid? And have you got the rear brakes up-graded as well , having run ds2500 and had nothing but issues the same as you mention with the same brake equipment I would lean away from them and into the direction of a full race pad from carbotech or hawk.

 

[red reading]

I found ds2500 caused warped disc feeling and cracked my high spec discs, ebc pads were wooden and shite,pagids fell apart from being overheated....I tried all sorts and had issue after issue with them and discs....now run carbotech xp 10 all round with smart car front discs redrilled on the rear and caliper spacers, and brembo front calipers running 310mm discs on bells with lips...I now have no issues what so ever on track or road. Also found drilled or grooved to the edge discs to be a night mare.....have had one rear disc crack but that was traced to a warped flange/rear spindle and the disc being put under a convex like compression.

 

[MarkTurbo]

Ben, i'd put money on your discs not being warped and deposits from the DS2500's being to blame ;-)

What size discs are you using and what calipers, fluid etc?

 

[fubar andy]

What size discs you using?you tried places like rally design

They are the K-Sport 304mm discs, but as the wait time is about 4 billion years I can't be waiting as I'm off to the MLR track day at Oulton Park on the 15th November (and yes the discs won't be delivered till the end of Novermber!)

As it's been mentioned it sounds like I've got deposits issues on my discs and I think it sounds like you've had the same.

I'm going to Iron X/clean my discs, plus clean my hubs and make sure my wheels bearings are in good nick (which I think they are)

 

[R called Jay]

Whenever i get any sort of warping i rub the disc back with emery cloth to remove any deposits and also flatten the pads off, and then try them again. But usually the difference is neglible and i end up getting them skimmed.
I run 330mm discs on the fronts using brembo calipers from a Fiat Coupe 20v turbo and at the mo only have dot 5 fluid in as I was flushing out some newly rebuilt rear calipers. Will be putting RBF 400 racing fluid back in before my next trackday. All pads are wearing evenly and pistons in the calipers all appear free.
The rears are 310mm discs with standard caliper fitted on spacers and currently using EBC red stuff pads.
Have any of you needed to make any ducting to your brakes or do you find the vents in thee bumper to be sufficient?

 

[vss irvine]

are they 2 piece discs andy?

what kind of offset do they have?

 

[fubar andy]

are they 2 piece discs andy?

what kind of offset do they have?

Yeah they are a 2 piece kit, not sure what the offset is tho?

 

[fubar andy]

I had all the issues you had Andy and mine was pads leaving deposits on the discs, was cured by a good clean up and carbotech xp10 all round....no issues at all now.

Just as an update, I Iron-X'd one of my discs this weekend and gave it a good scrub with a brush and sand paper.

I was amazing to see the disc go purple almost immediately when I added the Iron-X, after I had cleaned and rinsed it, it almost looked new (apart from all the small heat fracture on it)

Will sort out the other one this weekend when I'm free and then install my XP8's that have turned up and hopefully that should sort it out!