Best disc brake conversion for 71 fastback

Why not stay with the twin leading shoe? Add the stiffening mod and it works really well when adjusted properly.

Just my own opinion - I expect I’ll be shot down now......

The best disc brake conversion is the one Norton devised for the production racers: https://andover-norton.co.uk/en/shop-drawings/13 (there's even a twin-disc version if you really think it's necessary), but it's not cheap.

The cheapest option is to get a standard disc fork slider. The pinch-bolt side from your drum will do although the disc version is a little stiffer. Plus a standard disc wheel and disc. Fit an AP Racing caliper with an aluminium adapter plate to suit (available in the usual places). Then either get a standard brake master cyclinder, if you want to keep the original switchgear, and have the bore sleeved down to 13mm and use a longer lever from an AP Racing master cylinder. Or fit any one of the many master cylinders out there with a 13mm bore. The original Commando m/cyl bore is 5/8". The AP Racing m/cyl has the same bore so no more stop aside from the longer lever.

You're never going to get Fireblade braking, or indeed single finger braking of any kind, but that will at least stop you with a good handful.

The Norvil disc conversion is authentic, especially if you eschew the drilled discs, and together with a sleeved m/cyl will give you a good brake. Single disc is plenty. Option to use original disc wheel or one with Norvil hub.

Crikey !! I just looked at Andover's prices for the Norvil disc components. You're going to hate me for this but I was buying those hubs for a fiver a piece in 1988.

If you want more then there are several conversions to add a 305mm or even 320mm floating disc with a four piston caliper. All use the standard Commando fork leg and wheel. Again, single disc is plenty. And looking at Andover's prices, these might work out cheaper.

I'm with you on ditching the drum. I remember them from the '70s - worked twice then faded out on the third use, reinforcing plate or not.

I've done the stiffening kit mod and the brakes are better, I think a longer operating arm is also available, which should give more pressure to the shoes, does anyone have anything about this mod 

Regards Alan

To be aware of. If you are used to the fireplace brakes - incredibly powerful, squeeze until rear wheel is off the ground stuff, you might scare yourself a bit on the Commando.  The geometry is from a different generation. A big squeeze and you have a far greater chance of locking the front wheel on the Commando with all the drama that goes with that. 

A big squeeze and you have a far greater chance of locking the front wheel on the Commando with all the drama that goes with that. 

Correct, the thought was that if the disc was made more powerful than the drum then riders used to the drums would lock up the disc so they derated it by using the too large diameter master cylinder. But they missed the other consequence of the large diameter which was the wooden feel and the lack of control so the final big heave on the lever locks the brake.

The 13mm or 12.7mm sleeve conversion increases the leverage ratio closer to the ideal 27:1, the wooden feel goes and you get better control, more lever movement to move the same amount of fluid but less effort needed. 

Hi, I have seen Honda CB600 front ends recommended as a replacement for drum brake bikes in the Classic Mags. I was going to try a Suzuki GS750 front end until I found they have got quite pricey. I have a Yamaha 650 custom set going in my Atlas sometime. The bottom bearing is too big, but it will fit after remachining the bottom of the stem. I have a set of Triumph T140 Harris forks with twin discs, and they will fit most twin frames.

Picture tells the story.

this kit is known to be vg quality and works very well, from much feedback. It is not original, but that is not important to me, and function over style is the way to go for brakes, I say. Holland Norton Works should be able to supply more locally than Colorado. Otherwise, I would go for a ready made 13mm cylinder, not a conversion.

Unless you're racing, IMO the standard Norton brake disc and caliper plus an Andover uprated 13mm master cylinder is perfectly adequate for normal road use.

You retain original looks and with the 13mm cylinder you have the biggest single braking improvement to the standard factory set up.

If that normal road riding extends to a long descent down a mountain pass then get a better caliper too or take a few breaks on the way down for the caliper to cool. 

Hi John,

no breaks for my brakes.

I stay near the Austrian border, the alps are my playground.

Forgot to mention in my last post that I've sintered brake pads fitted also. 

"Unless you're racing, ..."

Strange as it might seem, for racing you want a consistent brake. It doesn't need to be particulary powerful - so long as everyone else runs similar. Which is typically the case racing a Commando as a classic with a 1972 cut-off. It's about hitting the braking points and predictable, controlled braking into the turn.

It's on the road where more powerfull brakes come into their own when someone parks a Ford Focus in front of you. Something that comes on strong and can then be eased back as the tyre protests.

An AP Racing caliper, with an adapter plate or a Norvil leg, is period correct, superior to, and probably cheaper and easier to find than the Norton Lockeed item. I see Andover offer a look-alike with a larger piston which might be worth a look.

My Commando has a floating disc and four piston caliper from a BMW paired with the original 5/8" master cylinder.

Hi Michael,

our Austrian friend took that photo of us, so sorry I don't know what camera or settings he used but that's his hobby so I expect he has fairly fancy equipment.

I think he's also provided action photos during previous Austrian NOC rallies.

Picture was taken 20/05/2011 using a Canon EOS 7D

Lens 16-35mm f/2.8-23

Exposure time 1/1000

Just browsing over a coffee and thought this must be the answer to Robins question...

that previous double disc photo: I have that set up on a Commando, with the original master cylinder, which works well due to extra caliper correcting the hydraulic mismatch  ( as tested on Norwegian fjord descents!). However, it is still not as good as  a modern twin disc . It also very pricey ( from Norvil as only supplier)

...just look "better" to my eyes, not that I speak with much experience of disc brakes on bikes.

From a purely mechanical POV, having 2 discs surely provide an equal force to both legs? Wouldn't a single disc provide some sort of vertical torque force, even if us mere mortals are not capable of discerning this- and wasnt there similar logic in Norton swapping the single disc from one leg to t'other on Commandos?

Asking for a friend...