Scored Brake Disc

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ntst8

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I have a front disc that has recently become scored :cry: so a couple of questions from the completely ignorant here.

1 - Is this bad luck or bad management, ie is there anything i should or should not have been doing to prevent this?

2 - The pad has a roughened area (hence the scoring) - Is the pad salvagable by smoothing it down (file?, presumeably not sanding or the grit would make things worse?)or should it be replaced.

Running a Grimeca caliper, ferodo pads (about 3yrs, 10,000miles old), aftermarket full floater disc (same age as pads). There is plenty of depth in the pads yet.

Thanks.
 

Ron L

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Since it is an aftermarket disc, I would suspect the metal used in the disc. A lot of these things are designed by well intentioned and talented people, but usually are bike enthusiasts like us, not brake engineers. I am still wanting to do a similar set up, but will probably go with something like a Brembo disc with an adapter or a custom made center. After playing with the old Dunstall double disc set up, I am appreciating the talents of real brake engineers.

If both your pad and disc are scored, I'd replace them both. If you can skim the disc by turning or grinding you might get another 10,000 miles, but these things are usually pretty thin to begin with. The pads are history, replace them. Sanding or filing is not a good idea as these often contain asbestos which is bad for your health in fine dust.
 

ntst8

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Thanks Ron,

the disc isn't overly thick so skimming isn't an option.
It looks like new pads now and i will start looking at disc options.

Cheers
 
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Stopping requires that you sacrifice disc surface. If you don't want the disc to look bad, then don't apply the brake!

If you ride fairly hard, discolouration and scoring of the disc is nomal.

Thank your lucky stars you have a disk brake. Whan I was testing the Commando, we had the Italian (don't remember the manuftcurer) twin leading shoe drum brake on the front. I found, by brittle-laquer stress testing, that the backplate distorted so much that the braking effect was reduced by about 50 percent under heavy braking.

The development of disc brakes for motorcycles was a typical British debacle. Management didn't grasp the concept of a floating caliper/fixed disc configuration and tried to develop a floating disc/fixed caliper set-up. The first concept had a disc mounted on a splined hub. With the caliper applying force close to the maximum radius of the disc (about 11"), the bending moment on the disc was enough to "cock" the free-floating disc so that it jammed on the splines, which had a radius of avbout 4". A second design was to put the disk on dowel pins. Same result.

Why the concept of a floatng caliper with one fixed pad and one moving pad, common to many automotive configurations, never occured to our designers, I'll never know.

In retrospect, I guess the design group were a bit "blinkered". There was essentially no dissemination of knowledge between the car and motorcycle communities.
 
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Are the scores depth relativly even around the disc? If not, check the floater mountings. They could be sticking and causing the disc to run a slight wobble. Also, you could check how true the disc carrier is.
If the grooves are reasonably even, it's not desireable to surface it, for several reasons. Generally, the more metal in the disc, the better your brakes work. A thicker rotor is less likely to crack and break. [Some discs are made with a slight waviness in the surface.(I don't know how!) This is to push the pads back off the surface to avoid glazing and overheating. This was told to me by a brake shop, in reference to Japanese bike brakes.] Some rotors are plated.
BTW, the stock Norton rotor is plated, and works better if this is removed and you get pads to match the under material. (can't recall if iron or steel)
Don't smooth the pads unless glazed, or you don't know the original location for them. Understand, the pads are already seated (worn in) to the rotor. A new pad surface will have to wear in before it makes full contact and thus generate maximum stopping ability. In fact, if heavily scored, you could overheat the pad just in normal riding due to the resultant small surface in contact. This spot glazing can be so bad that the pads never wear in. This also does bad things to the rotor.
If you do smooth the pads, use a very course grade of sandpaper taped down to a flat surface. The large grit should not embed into the pad. After, spray with brakekleen and rub across a sheet of metal, paper, etc, to verify nothing is embedded.
I use a piece of plate glass under the sandpaper.
 

ntst8

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Thanks Jota,

have pulled things apart, disc and carrier seem to be true and the score is consistant around the disc. Seems like i might have a rare Amal brake - a bit of galling going on? :lol:
I suspect Ron may have hit the mark as the disc came from a reputable spares shop but was made for them rather than being from a name source.
I still have the stock disc, which had been milled and drilled by the PO. Have read varying opinions on the wisdom of drilling the stock unit and liked the look of the bigger floater hence the change.
Perhaps for the replacement i can find one of those new fangled rotors with the profiled edge - just to annoy the purists.
 
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