Disc Skim At 50k?

[Ogben Schmutzel]

Hi All,

 

Just got through the MOT but was advised that front pads had about 3,000 miles left in them and that when they are done the disc's will need skimming!!

 

I realise that it will depend on driving style and things but in general do the disc's really need skimming at that mileage or could I do it myself and let them bed in?

 

Cheers.

Oggy

[johnb80]

For the cost of the discs it's not worth messing about skimming them.

 

Regards - JB

[Ogben Schmutzel]

They've got some kit for doing it on the car.

 

[El Dingo]

They could need doing at 50 miles, let alone 50k.

 

One of the worst things you can do is brake hard from high speed to a stop then sit with your foot hard on the brake pedal - where the pads sit retains the heat, and the rest of the disc cools more quickly. The heat differential can cause the discs to warp.

 

I agree with Johnb80 - buy new ones.

[Guest galaxykid]

I just replaced my front disc's and pads at 45793 miles the pads were shot .5mm left on the inner pad 1.5mm left on the outer pad, the disc's were well inside the wear limit but the fins in the vented section had rusted away :D I think one more good push on the pedal in the wrong spot and they could have shattered! this week end will hopefully see me changeing the rears pads out as they are getting a bit low and make noise under heavy brakeing :D

as to haveing your disc's skimmed? are they warped? any bad scouring in the brakeing surface? will there be enough meat left in the disc's afterwards? it may be as Johnb80 says cheaper to replace the disc's and be done with it ;)

[Justice]

@

[johnb80]

There's also the cost of labour involved removing and re-fitting. At the end of it all you may have extended the life of the disks by another 20-30K. So

[Masked Marauder]

Discs are hardened, as the disks are used the hardened layer wears away, however the heat from braking hardens the metal below the hardened surface and all is well.

 

When you skim them they loose the hardened layer and it wears too much to build the heat up to harden the metal below as you go. So the discs will be gone double quick after you skim them.

 

For this reason we use new disks and drums on the trucks and trailers at work, skimming is a false economy in every sense.

 

As for skimming on the car I have NEVER heard of that one before, and a search on Google and asking the fitters at work throws up a blank too. Skimming needs to be done on a lathe, both sides of the disk, and needs to be balanced and inspected afterwards. My suspision is they are intending to wire-brush them and bill you for a skim.

[Ivor]

I replaced mine at 50K, the vents in the discs were rusty/scaled and well as the surface being worn.

[bigdaddy]

Does the garage mean by skimming,,,,,,,,,,to skim off the little lip at the edge of the disc

 

For the cost of a new set of discs and pads,,,,,,,it is not worth the hassle to get the discs skimmed

[johnb80]

I would have thought the heating and gentle cooling would have annealed the metal not hardened it? Case hardening of brake disks wouldn't be a good scheme either. I'm notr convinced of your logic! The discs I've looked at looked no different to straight forward cast iron.

 

Regards - JB

[Masked Marauder]

Was just relaying what I was told last night at work.

[strouf]

As for skimming on the car I have NEVER heard of that one before,

There's a device (made by Snap-on) I think, that does the skimming while disks are on the car.

[johnb80]

And all the nice little metal grindings attach themselves to the abs gear and knacker it up completely.

 

NO THANKS :D

[El Dingo]

I quite agree - no thank you to skimming. I'm surprised if Snap-On make such a device, but then you never know. Some well respected peeps think that oil suction devices are a brilliant idea (you know, to do an oil change). Some people even like diesels.

 

(BTW to anneal you need to heat and then quench.)

[NikpV]

(BTW to anneal you need to heat and then quench.)

 

I though harden was heat then quench (oil or water) and anneal was heat and slow cool :blink:

[johnb80]

Correct

[johnb80]

(BTW to anneal you need to heat and then quench.)

Back to school time for you my boy. heat and quench will harden metal (with a couple of exceptions) heat and slow cool will anneal.

 

Regards - JB

[Guest Snooper601]

You will be very lucky to get more than 80K out of a set of discs, 2 sets of pads at 40K each.

 

Pards are much harder than when they used asbestos in them, so the discs now take the wear.

 

BTW don't believe any dealer who says your rear pads need changing at 20K like mine tried to!

 

I politely declined his offer and then measured them, then again at 25K and then just before 30K. I then went in for the 30K service and told them that I had calculated that the pads would all last beyond 40K, just, so they could do them then. :rolleyes:

 

Cheers

[El Dingo]

(BTW to anneal you need to heat and then quench.)

Back to school time for you my boy. heat and quench will harden metal (with a couple of exceptions) heat and slow cool will anneal.

 

Regards - JB

Really?

 

Then my wire annealing machine didn't work? Hmmm. :blink:

 

So, case hardening, involving heating and slow colling in carbon is annealing, is it? :P

[El Dingo]

Quote: What makes materials hard is a complicated subject that has to do with internal crystal structures. These in turn are effected by heat treating or mechanical working. Most non-ferrous metals can only be hardened by "work hardening", hammering, rolling, bending. But they can be softened by "annealing" which is heating to a red heat and then cooling quickly (opposite to steel, see below).

Unquote:

 

:blink:

Yep, I'll go back to school - my machine annealed copper. I forgot about steel.... Hmmm copper brake discs... is that what coppaslip is for???

[sepulchrave]

Additionally, I really WOULDN'T buy disks from ebay!

 

Galaxy's warp the best quality disks with monotonous regularity, get some Brembo OE pattern disks from GSF they're really good with the Pagid HD pads, I think I paid about

[Guest Snooper601]

Additionally, I really WOULDN'T buy disks from ebay!

 

Galaxy's warp the best quality disks with monotonous regularity, get some Brembo OE pattern disks from GSF they're really good with the Pagid HD pads, I think I paid about

[Masked Marauder]

From my personal research the biggest cause of warped front discs is drivers holding the vehicle on the foot brake after they have stopped. This causes localised heat build-up as the discs take up the heat from the pads as the rest of the disc cools. Warping is sure to follow....

[sepulchrave]

That's true too, but the received wisdom is that those wretched recycled chinese disks off ebay don't last too well either.

 

I would say that my Sharan is quite dramatically under braked for a 1.75 tonne vehicle capable of 135 mph!

 

After all they are my children and I wouldn't use remoulds either. :D