Installing a Front Disc Brake on a Series ‘C’

davidd

Well Known and Active Forum User
VOC Member
If I were upgrading the front brakes for the sake of better braking I would approach the project as if I were improving an entire system. I would first eliminate anything that I believed detracted from maximum braking. As I have mentioned before, the position of the lower link can increase or decrease the effective braking. If the link is parallel to the road (or lower) the braking is 100%. If the eccentrics are riding higher than that, the braking is probably 25-35% less effective, no matter what brakes you have. Replacing stock brakes with discs will lead mostly to much easier ineffective braking. I believe that TT mentioned applying the disc brakes on a Vincent and watching as the fork went from laden to full extension. Does the bike slow? Yes, but it is also involved in a lot of non-compliant behavior that erodes good braking traction. The discs will enhance or exaggerate the action, but it will not abate it.

In choosing the calipers and discs, I would select a flat disc. This will allow the carrier for the disc to be a very simple design that is easily turned up quickly on a lathe. You will probably choose the discs and calipers together. For a twin I would go with 11-12" and at least a two piston caliper. Whatever is easily available at the breakers, but still supported by the manufacturer. I think a large disc works better on a large wheel providing a much better rim to brake leverage ratio.

For the master cylinder I would use the unit that was available as stock. I would not use the BMW unit because at this point I feel it would be honoring style more than form. Justin had an issue with mounting the master cylinder on the Prince because of the lack of room between the handlebars and cowl so an alternative was used. I found a radial master cylinder that worked really well and and it provided him with what he desired, but the mechanical pairing must be done. With a matched system you can be really lazy and end up with a wonderful brake.

This is similar to the approach taken with Sam's brakes and they have proved to be wildly successful. I think he paid $100 for all the parts on Ebay and he used the 14" springs. You can see the attitude of the lower link in the photo.

Best of luck,

David
 

CarlHungness

Well Known and Active Forum User
VOC Member
Justin used the disc brake set up that I made as a pattern to make his own. He mounted the calipers below the fender stay because he was concerned about clearing the Prince Fender, although I believe the calipers would have fit. I used the Kawasaki parts for the first attempt. When Sam Manganaro wanted a set I suggested the Susuki TL 1000 brakes, which were becoming readily available at that time. It was a very easy build. I liked the TL discs because you could use a flat carrier which made the machining straight forward. The caliper mounts were based on my originals. The only change was to the shape of the mount where the calipers attached. They were changed only to accommodate the different caliper mounts. If I were building some today I would use something more modern that was plentiful. I would not use a single piston or anything too old because the performance goes way down.

Here is Sam's bike:

View attachment 12548

This PDF is a tracing of the caliper mounts. It is a tracing, so it can be scaled for a full size template. I used 4130, if I remember correctly. The lowest hole is for the axle. The hole directly above in a straight line is for the brake anchor, which is now a bolt instead of just a peg. The remaining two holes are for the caliper mount. I milled out a small amount of material on the inside of the mount around the axle. It was milled to the thickness of the the brake plate, so it takes no more room on the axle, except, the nuts are on the inside of the plate rather than the outside.

I think the plate was 1/4" or so. The flat side of the plate is bolted to the inside of the Girdraulic through the anchor hole and the axle. The milled portion on the inside of the plate just mimics the brake plate.

David
Hi: I like the Suzuki TL 1000 discs, and wondering what it would take to install the speed drive. I don't see one on Sam's bike
 

CarlHungness

Well Known and Active Forum User
VOC Member
Hi Carl,

Care to tell us the reason(s) why you are planning to replace the TLS brake you only recently installed? I only ask as I know a few folks are considering installing TLS and your experience with it would be of value to all.

regards

Martyn
HI: I have not installed them yet, still in the box. They are fitted to my drums and I plan to sell the whole plot, with my Shadow drums. They look great, but do have a (slight?) tendency to lock up if wet. I am throwing looks to the wind here, as I feel I need a disc brake up front. Robert Watson, a fast rider speaks highly of the TLS set he installed. Yet I agree with journeyman Roy Cross, if you're going to modify the front brake, you can't beat the disc. Besides, my bike is a 1954 and discs were available then, just. The mod can be changed back to stock with little effort.
 

CarlHungness

Well Known and Active Forum User
VOC Member
If I were upgrading the front brakes for the sake of better braking I would approach the project as if I were improving an entire system. I would first eliminate anything that I believed detracted from maximum braking. As I have mentioned before, the position of the lower link can increase or decrease the effective braking. If the link is parallel to the road (or lower) the braking is 100%. If the eccentrics are riding higher than that, the braking is probably 25-35% less effective, no matter what brakes you have. Replacing stock brakes with discs will lead mostly to much easier ineffective braking. I believe that TT mentioned applying the disc brakes on a Vincent and watching as the fork went from laden to full extension. Does the bike slow? Yes, but it is also involved in a lot of non-compliant behavior that erodes good braking traction. The discs will enhance or exaggerate the action, but it will not abate it.

In choosing the calipers and discs, I would select a flat disc. This will allow the carrier for the disc to be a very simple design that is easily turned up quickly on a lathe. You will probably choose the discs and calipers together. For a twin I would go with 11-12" and at least a two piston caliper. Whatever is easily available at the breakers, but still supported by the manufacturer. I think a large disc works better on a large wheel providing a much better rim to brake leverage ratio.

For the master cylinder I would use the unit that was available as stock. I would not use the BMW unit because at this point I feel it would be honoring style more than form. Justin had an issue with mounting the master cylinder on the Prince because of the lack of room between the handlebars and cowl so an alternative was used. I found a radial master cylinder that worked really well and and it provided him with what he desired, but the mechanical pairing must be done. With a matched system you can be really lazy and end up with a wonderful brake.

This is similar to the approach taken with Sam's brakes and they have proved to be wildly successful. I think he paid $100 for all the parts on Ebay and he used the 14" springs. You can see the attitude of the lower link in the photo.

Best of luck,

David
Hi: Thanks for the advice, especially on the link angle. You can see I'm trying to have someone else make some decisions for me on the precise disc/caliper/master cyl. combination. I have collected a nice store of info and will continue to slog through. As noted, I want to retain the stock speedo drive as well, so I'm still scratching.
 

davidd

Well Known and Active Forum User
VOC Member
Hi: Thanks for the advice, especially on the link angle. You can see I'm trying to have someone else make some decisions for me on the precise disc/caliper/master cyl. combination. I have collected a nice store of info and will continue to slog through. As noted, I want to retain the stock speedo drive as well, so I'm still scratching.

Justin put the speedo drive on the rear and used the stock items with a long cable. Sam and I used inexpensive bicycle speedos, which can be programmed to the size of your tire.

David
 

b'knighted

Well Known and Active Forum User
VOC Member
With the modern trend of returning bikes to standard, I wonder if anyone has a removed disc set-up, which they'd like to sell, languishing under their bench.
 

Sakura

Well Known and Active Forum User
Non-VOC Member
If you want disc brakes, oversized engines, 5 speed gearboxes etc, etc, why not buy a modern bike and get all the superior reliability, braking etc that comes as standard? I ride classic, veteran and vintage bikes to enjoy the experience that riders had back in the day. Personally I ride according to my brakes and road conditions. When you're riding a veteran with a stirrup front and dummy rim rear, a standard Vincent's brakes seem awfully good. Just my view of course!!
 

vibrac

Well Known and Active Forum User
VOC Member
When you have invested decades in a machine it's hard to loose all that knowledge I do have a modern machine and I enjoy it I also have a belt drive stirrup front brakes machine and I enjoy that but most of all I enjoy my workshop and modifying my Vincent (but not permenent modifications) there's not many mods you can do to a 21st century bike
 
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