disk brake conversion

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Apr 15, 2004
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I'm accumulating parts to replace the pathetic drum brake on my bike with a disk. Am thinking of using the stock rotor and caliper with maybe a Magura master cylinder.

My questions:

I noticed in my parts list that the fork slider on the non-disk side has a different p/n than the drum brake slider. Do I need to get new sliders on both sides or just the one with the caliper mounts?

Also, I've noticed that occasionally I see a bike with the disk on the left and caliper on the front. What's up with that? Did the owner or factory just put the forks on backwards or is there some reason for reversing it?

The '75 and newer models had the disc on the left front. I've never heard a good reason for the change; maybe to counteract fork flex? It does look weird though. Also the MK III's didn't have the front hoop on the fender.
Are you sure you want a disc? Vintage Brake can turn that drum into something to equal or be better than the stock contraption.
vintagebrakes wants $500 and has a 12 week turnaround time. For that I can do a disk conversion then start saving up for the brembo parts. Then someday I'll have a *really* nice front brake.

And maybe I'm being pessimistic but I just don't believe that drum brake could ever be made anywhere near as good even as the stock disk. For puttering around the farm roads on Sunday morning I suppose the drum would be ok. I want a real brake though.

The disc brake sliders are oval in external dimension (more meat at front and rear than on sides) while the drum sliders are round. Supposedly this is for additional strength for the "high" braking forces with the disc. While you can use the left drum brake slider with the right side disc slider, they will be visually different.
Thanks. That's good to know. Guess I'll be looking for both sliders then. I want the bike to look right.

Yes, the 75 Mark III e-start has the brake on the left. they moved it to counter act the forces of the rear rotor on the right.
It amazes me they would put that much thought into balance / forces and build it with the wheels 1/2" out of alignment.

Please make sure your drum brake is adjusted properly before you chunk it for a disc. I currently have a '75 Commando with a stock front disc brake and I can honestly say that it is no better than my old '69 Commando drum brake.

I'm going to look at the brake this weekend and see if there's anything I can do to improve it. Right now I don't feel safe to riding in traffic with that thing.

I don't think I've ever experienced a drum front brake that's in the same league as a disk. My dad's old water buffalo had a pretty powerful brake but it was grabby.The dual disks on the GS1000 he bought later were infinitely better. Just no comparison. So I guess I tend to have a low opinion of drum brakes.


I have purchased the Brembo Master Cylinder from CNW & am very happy with the way my stock Norton disc brake works now !!!!!

Norton owners talk about resizing the original norton master cylinder to reduce line pressure etc etc. But some have told me they notice little improvement for the cost involved.

My suggestion would be just to get the Brembo Master Cylinder and hook that up, you will be happy I am certain. No waste of money here.

You will have to get a new line from the master cylinder made up which most brake or hydraulics people can do in 15 minutes.

My front brake feels fantastic, you won't be disappointed.
Hi Debbie,

I have a disk on my 73 850. I kept the stock caliper and changed out the Master Cylinder to a Magura. Grimica also makes a good M/C. I then added a Stainless steel hose, replacing the stock rubber one.

I have a two finger brake on the front, have never had a concern or problem with stopping.

I do have a set of sliders at home in Las Vegas for disk brake. If you are interested in them let me know.
Hi Dave,

That's exactly what I'm planning to do. Thought I could use either a Magura or Brembo master cylinder. I can buy a Magura from Dennis Kirk for about half what the Norton suppliers charge for a Brembo. So that's probably what I'll do.

Was wondering what you did about the switch cluster?

Questions, I have more questions. Always more questions. For today, I'm pondering a couple of small issues:

I'm sending my old well-used rotor out for resurfacing. Should I have it drilled also? The vintagebrakes website says don't drill the "gray iron" rotors but doesn't say why. I suppose I should ask him but was wondering what you all think about that. They certainly look cool drilled. Not sure if there's any benefit otherwise...

I'll have to get a brake line made to mate the new master cylinder with the stock caliper. Stock has a little steel pipe that connects to the caliper and the rubber hose connects to that near the top of the slider. Should I just have a new SS line made that runs all the way to the caliper or is there a good reason to use the steel pipe? (If so I'll have to buy one along with the mtg bracket. Don't have all the small bits yet).

The steel tube is optional. It's a matter of cosmetic appeal. The steel tube allows the hose to stay tighter in line with the slider. The one piece 'sometimes' gets a little sloppy.
My Magura does not have a mirror mount. I believe the Brembo does. If your running bar end mirrors or left only, it's no big deal. Just something else to look at.
Rockypointcycle.com has the Magura and a switch cluster. The switch cluster is made by K & S and features Hi / Lo, turn, horn, hi flash and maybe more. It is black and looks nice. It goes on the left and replaces all your switch clusters. It's just a little bigger than I would like, but not bad.
K & S makes other switches, I don't know were to get them.
Other people have gotten creative and used Japenese, BMW and even Ducati.
I think the switch issue has already been discussed somewhere on this forum. Any way, I like the late Ducati switchgear. Small, clean, functional, cheap (eBay). The right side gives you a kill switch and starter button (not needed).
You'll need a matching clutch lever for the Magura, so get one from Dennis Kirk also. It will come with a barrel for the clutch cable. Use a Ducati left switch to match for turn signal and Hi/Lo beam and passing flash. Alternatively, K&S makes a nice left switch for everything but a kill button. More expensive than a used Ducati one though. And you will need some type of push-to-open switch or toggle for a kill switch or a push-to-ground connected to the Boyer signal wire (not feed wire!).
Switch Cluster

Hi Debby,

I removed the Lucas switches and ran a Magura switch on the left. If you check out Jerry's Norton page, look in pics, he had one posted of my handle bar set up I sent his way.

Just about any switch that has the components you want and will fit your bars will work.

You can even look to a bike salvage yard and pull a switch cluster off another bike.
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