RE: Skim Those Disks
Thursday 30th January 2003
Skim Those Disks
While they're still on the car...
Discussion
My previous car had the discs skimmed on the car.
Don't know how it was does because I wasn't there (car was left in the capable hands of a trusted mechanic for the day for an MOT/service)
Got the impression it was some sort of machinery mounted on the hub though.
The results were fantastic, the braking was perfectly true and smooth. (1996 Honda Civic Vti running EBC grooved discs by the way)
Don't know how it was does because I wasn't there (car was left in the capable hands of a trusted mechanic for the day for an MOT/service)
Got the impression it was some sort of machinery mounted on the hub though.
The results were fantastic, the braking was perfectly true and smooth. (1996 Honda Civic Vti running EBC grooved discs by the way)
If discs are slightly warped they can be skimmed to make them true again.
Another theory is that there can be an eency weency imperfection between the hub and the disc which means that a disc skimmed on the car will match the hub it's mounted on.
Scream in horror and call my mechanic a cowboy if you want but the brakes were perfect on the car after the process I described.
Another theory is that there can be an eency weency imperfection between the hub and the disc which means that a disc skimmed on the car will match the hub it's mounted on.
Scream in horror and call my mechanic a cowboy if you want but the brakes were perfect on the car after the process I described.
Forget it. Itd be better to just replace the discs if theyre that bad.
Theres been a similar device around for the trade for years, works in exactly the same way, except the cutting heads are not the pads, but an attachment thats fixed to the machine.
It still uses the car to power the discs.
Seems like a false economy device to me, and in any case, youd still have to replace the pads afterwards as theyd be as worn as the discs.
Theres been a similar device around for the trade for years, works in exactly the same way, except the cutting heads are not the pads, but an attachment thats fixed to the machine.
It still uses the car to power the discs.
Seems like a false economy device to me, and in any case, youd still have to replace the pads afterwards as theyd be as worn as the discs.
If your car or your driving style results in warped discs (me and my old prelude vtec) then skimming them is a god send. I don't know how it can possibly be a false economy when although skimming the discs is cheaper than buying a new disc but what you end up with is a disc still within tolerances (ie, often a thicker disc than if you'd simply worn it down) and a disc that runs perfectly true especially when you consider (as someone else pointed out) you don't get a perfectly true disc from new because of slight hub imperfections.
Regards,
Mark
Edited to say: the only thing that would concern me is that when discs are normally skimmed on the car they are done one at a time to and they ensure that what you end up with is the same thickness on each side. With this invention I can't see how that can be done because surely if you apply drive and braking forces at the same time your limited slip diff will kick in and allow one of the wheels to be driven more than the other and the wear to the disc will be uneven. Given that the braking cycle is 2 seconds twice then abrasive/braking force must be quite high and must make this effect even worse - or is that not right?
>> Edited by dern on Thursday 30th January 17:50
Regards,
Mark
Edited to say: the only thing that would concern me is that when discs are normally skimmed on the car they are done one at a time to and they ensure that what you end up with is the same thickness on each side. With this invention I can't see how that can be done because surely if you apply drive and braking forces at the same time your limited slip diff will kick in and allow one of the wheels to be driven more than the other and the wear to the disc will be uneven. Given that the braking cycle is 2 seconds twice then abrasive/braking force must be quite high and must make this effect even worse - or is that not right?
>> Edited by dern on Thursday 30th January 17:50
If the disc is warped then the face of the disc moves towards and away from the pad face as it rotates. If there is pressure on the pad (brakes on) then the pad will follow the face of the disc and also move in and out. The movement of the pad will be transmitted hydraulically back to the brake pedal causing the pedal to pulse under your foot. When the discs are warped and the brakes are not on then the pad are push outwards slightly to accomodate the widest bit of the disc so when you first press the brake there is possibly some space to be made up before you contact the disc. If you skim the disc then you remove the outer surface of the disc until this movement of the disc face is stopped. I guess that if the discs are vented then the inner vent would still appear warped (albeit slightly as the warping isn't huge) but the face of the disc wouldn't be because of the skimming. I guess the only issue with this is that you no longer have a uniform amount of metal around the vent so heat distribution may be an issue.
Tabs said: I can't see how this system can help with warped discs. Surely, when the calipers operate, the pads will follow the discs, because either the calipers 'float', or the pistons go in and out with the warp? I just fit new discs on every other pad change.
Mark
Gentlemen (and ladies), I refer all of you to the web-site as follows: www.stoptech.com/whitepapers/warped_rotors_myth.htm IMHO all this new 'process' does is remove the burnt on pad residue, and as such would appear to be a good idea.
I like the idea but have a few reservations:
1. As has already been said, you have no control over which face of the disc gets more metal taken off. This is especially true on single piston sliding callipers where it is very common to see more wear on one face than the other.
2. If the discs are worn such that the faces aren't parallel, (i.e. tapered from the rim to the hub) the pads will have worn to match. Sticking a hard pad on the worn brake pad will mean the discs get ground smooth but not necessarily flat i.e. you might end up with discs that are thicker at the perimeter than they are near the centre (or the other way round).
3. Modern asbestos-free pads are so hard that the discs on most modern cars wear almost as fast as the pads (well, OK, a bit of an exaggeration but you know what I mean). Added to that, the manufacturers don't make them any thicker than they need to so by the time there's any appreciable lip on the edge of the discs, the main part is likely to be so close to the minimum permitted thickness that its hardly worth grinding them. (IMHO)
On the other hand, if you've had a siezed calliper and there's a rusty circle on one side of the disc but its otherwise OK, I guess these pads would be perfect for the job. I also like the idea of using them to "bust the glaze" on the disc and just get rid of the pad residue.
1. As has already been said, you have no control over which face of the disc gets more metal taken off. This is especially true on single piston sliding callipers where it is very common to see more wear on one face than the other.
2. If the discs are worn such that the faces aren't parallel, (i.e. tapered from the rim to the hub) the pads will have worn to match. Sticking a hard pad on the worn brake pad will mean the discs get ground smooth but not necessarily flat i.e. you might end up with discs that are thicker at the perimeter than they are near the centre (or the other way round).
3. Modern asbestos-free pads are so hard that the discs on most modern cars wear almost as fast as the pads (well, OK, a bit of an exaggeration but you know what I mean). Added to that, the manufacturers don't make them any thicker than they need to so by the time there's any appreciable lip on the edge of the discs, the main part is likely to be so close to the minimum permitted thickness that its hardly worth grinding them. (IMHO)
On the other hand, if you've had a siezed calliper and there's a rusty circle on one side of the disc but its otherwise OK, I guess these pads would be perfect for the job. I also like the idea of using them to "bust the glaze" on the disc and just get rid of the pad residue.
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