Brake Discs.

I've done minimal mileage on my 73 750 since purchase 12 months ago, mostly due to being as just happy to tinker with it as ride it !

I took it for its MOT (annual inspection) last weekend.
They advised "Front brake disc worn" so I'm looking at the options for replacement.

I have a fitted a Brembo front m/cyl and stainless brake line, with a rebuilt stock caliper.

The brake is now pretty good, but any improvement gained through disc replacement would be a bonus.
I have seen the ebay "made in India" items £48, and Rgm list replacements too, I like the look of Old Britts drilled items so something like that would be cool.

What are you guys using ?

CNW Brembo single disc kit; best single set up I have experienced!

nortonspeed said:

CNW Brembo single disc kit; best single set up I have experienced!

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Love the look, but I'm just after a (preferably good looking) effective replacement.
I can't really justify a big expense due to my limited mileage. :?

Steve
RGM is good stuff, which disc are you looking at? Have you modifed the master cylinder yet. That is a must.

stevetoxic said:

I took it for its MOT (annual inspection) last weekend.
They advised "Front brake disc worn" so I'm looking at the options for replacement.

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I don't know anything about UK inspections but I'm wondering about your result - did they describe the "wear" and explain why they commented on it and did it cause the bike to fail the inspection or was it just a recommendation? I inspect bikes for a living here in Pennsylvania and a rotor would fail only if it was too thin relative to specifications, or severely grooved or cracked, etc.

Rotors become "worn" the first time the brake is applied; the question is HOW worn? Since you say you're basically happy with the brake's performance, and unhappy about putting too much money out (who isn't?), then if it were me I'd assess how necessary a replacement actually is with respect to safety. If they failed it, of course, my thoughts are moot.

Once the chrome rubbed off and maybe lots of holes taking out spin inertia its more the brake pads composition you should be shopping for.

VintAge said:

stevetoxic said:

I took it for its MOT (annual inspection) last weekend.
They advised "Front brake disc worn" so I'm looking at the options for replacement.

Click to expand...

I don't know anything about UK inspections but I'm wondering about your result - did they describe the "wear" and explain why they commented on it and did it cause the bike to fail the inspection or was it just a recommendation? I inspect bikes for a living here in Pennsylvania and a rotor would fail only if it was too thin relative to specifications, or severely grooved or cracked, etc.

Rotors become "worn" the first time the brake is applied; the question is HOW worn? Since you say you're basically happy with the brake's performance, and unhappy about putting too much money out (who isn't?), then if it were me I'd assess how necessary a replacement actually is with respect to safety. If they failed it, of course, my thoughts are moot.

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The bike passed inspection, it was an "adsvisory"
But I've always thought the disc was pretty ugly :shock: with some scoring/wear and replacing was on the to do list.

With the £40 ebay brembo M/cyl the brake was transformed. (recomended)

I've had Norvils lightweight discs and they have all worn the carrier on the bobbin location at low or very low milages and effectively become scrap. Personally I'd avoid these. It's a shame really as I quite like the look.

stevetoxic wrote;

I like the look of Old Britts drilled items so something like that would be cool.

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I've drilled my (now standard) rear disc to a similar pattern to the Oldbritts myself. The brake discs are really quite soft and easy to drill, especially if you have a drill press. You just have to spend some time (in my case) with a degree wheel and some cardboard to make an accurate template prior to drilling. The drill bits including the counter sink tool cost me about £30 IIRC?

What is the minimum thickness (thinness ?) of a Commando front brake disk ?

Nothing written on it, stamped or cast on it, nor in the specs...

I do not believe nor ever heard of any factory rotor ever wearing out. Some have fractured after improper drilling or rusted pitted too much put up with but not worn out by use. So no factory published minimum or list discussed other than a trim to get the chrome off and not use normal radial spiral machine method but cross grind non in line with the friction translation surfaces. 5 Kidney shaped cut outs with 128 holes is lightest Norton disc I've seen at 1.5 lb less than factory, Then ya can jump Norton fence to modern thin lacy wonders.

Rohan said:

What is the minimum thickness (thinness ?) of a Commando front brake disk ?

Nothing written on it, stamped or cast on it, nor in the specs...

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I think .25in

I'm counting on the Lockheed caliper piston pucks to be able to extend enough to grip a wave rotor which is about as thin as they get, like 1/3rd Nortons dinner plate. Norton's dam tough stuff tough so likely over thick for most serious race heating distortion resisting no public legal issues thick and then some. The issue ain't so much of it fracturing as it distorting for weird grip reactions and over heating the fluid. Also extra dicy in Norton rotor because of how wide the friction surface is, so, the inner parts don't get swept as hot as the outer faster path, so guess what that does and why the hottest brakes around have narrowest friction bands and a bunch of tiny pucks to make up the surface area loss.


Ya know Ole Burt Munroe would of just gone thinner and thinner each race till it crashed him then, while healing, make another just short of that by a few less laps of abrasive then move on to the next over built component, like amount of rubber on the cords...

If adding stopping power simply is what you want I put AP Racing pads in and even the stock setup stops a lot better.

Pesumably they wince at the er ' chrome ' , unless its scoured .

Machineing it flat could be easiest . Theyrell be a Min service thickness though . Discs ordinarilly thicker than the unmachined inner area .

what thickness is the standard size Norvil disc?