Installing a Front Disc Brake on a Series ‘C’

[Bill Thomas]

Dear Bill,
I've also come across discs in the past that are not great in the rain. Early disc brakes on bikes were often cast iron that indeed did go a bit rusty. I remember early MotoGuzzi had iron discs. Perhaps a bit of rust gave the pads something to grab on. Later stainless or non-rusting materials were used some of which were just as bad when wet. Most discs used now are drilled which makes them lighter and helps dissipate any water. The right pads to match the disc material makes a big difference to working in the wet and having minimal

The first disc I wanted, was a Yam' Stainless, We have to look smart !!, But was later told they didn't work very well, This was in the 70s, With a set of TeleForks, The supplier messed me about for ages,
So I bought second hand Commando forks complete, And fitted Alloy race yokes.
I seem to remember Honda did a small plastic guard, To stop water getting on to the discs.
Cheers Bill.

 

[davidd]

Andrew,

I never had alignment problems with the disc brake calipers. It may have been that I was lucky. I machined the two caliper mounts together and they attach to the forks through the axle hole and a bolt through the brake anchor, so there was no float in my caliper mount set-up.

As Tim mentions, the Bramptons tend to bend with a good drum brake. Kal Karrick bent the fork on his Series A twin racer in his first race outing with a Series A brake. The Brampton forks need the tiny brace that was done on the TT machines, at a minimum.

I stopped investing time in disc brake conversions when I started to race because I had to use drum brakes by rule. Drum brakes can be a lot more powerful than disc brakes, but as the drums become more powerful, they become less stable also, meaning that they can be grabby. Disc brakes rarely become grabby.

The reason drums can be more powerful than discs is because the drums with even a single leading shoe use the geometry and the friction of the lining to become self energizing. The disc does not have much self energizing, thus the need for hydraulics to increase the work the calipers do.

Vincent Speet's brake is designed to self energize a great deal, maybe something like 300% more than the stock drum. The 8" brake is maybe 100% more than the stock brake. Both brakes can perform much better or much worse by adjusting the coefficient of friction on the brake linings. Unfortunately, that is a more tedious process than just squeezing the lever of your disc brake harder! So, I think disc brakes are a good solution to better braking performance on a Vincent. For those who want to stick to drums I think Vincent Speet's brakes will do the job nicely.

David

 

[vibrac]

Perhaps that prompts me to ask why hydraulic drum brakes were tried so little in those years before discs when they were already plentiful on cars, is that option re-visitable with modern parts? I would have thought that would have ticked a few boxes at a much lower cost than new brakes

 

[davidd]

Perhaps that prompts me to ask why hydraulic drum brakes were tried so little in those years before discs when they were already plentiful on cars, is that option re-visitable with modern parts? I would have thought that would have ticked a few boxes at a much lower cost than new brakes

Tim,

I think it is an option to use hydraulic drum brakes. The reason you don't see many hydraulic drum brakes on motorcycles is the the manual drum brake is so powerful. The drum brake has to be detuned quite a bit to make it stable when aided by hydraulic pressure, like using low friction linings or twin trailing shoes, the latter being the most stable set-up. I would guess that most cars that use rear drums have very carefully matched friction coefficients for their linings.

However, if you think of using hydraulics on a stock Vincent drum I think it would do well, except that it would highlight the horrible pre-existing problems like the poorly designed brake shoes and the low friction linings provided as originals and replacements. The shoes would be bent into pretzels.

I think a better way is to design better shoes and experiment with high friction linings to see what optimal braking with the almost stock brakes are. This might provide some good results. If it does not, we can spend our money with Vincent Speet or the Club and get a better designed brake.

The alternative to both is the disc brake conversion. This is ideal for someone riding with modern bikes because it will provide similar braking performance. This is one of the reasons why I like large rotors. I don't think it is the best idea to make a weak disc brake simply because it is stronger than a poorly set up Vincent brake.

David

 

[andrew peters]

The first disc I wanted, was a Yam' Stainless, We have to look smart !!, But was later told they didn't work very well, This was in the 70s, With a set of TeleForks, The supplier messed me about for ages,
So I bought second hand Commando forks complete, And fitted Alloy race yokes.
I seem to remember Honda did a small plastic guard, To stop water getting on to the discs.
Cheers Bill.

73 up Hondas had the plastic "splash guard" behind the fork leg, the caliper was in front of the leg, not really sure what it did but I don't think it kept the disc dry...

 

[andrew peters]

Perhaps that prompts me to ask why hydraulic drum brakes were tried so little in those years before discs when they were already plentiful on cars, is that option re-visitable with modern parts? I would have thought that would have ticked a few boxes at a much lower cost than new brakes

60s and 70s Harleys had a hydraulic rear drum... a single leading shoe, it really was no better than the mechanical drum, they stuck with the big mechanical drum on the front... Harleys really aren't a good example to use when thinking of good brakes, they had large drums that were hopeless, in fact a performance mod in the US was to remove excess weight and who needs a heavy brake that doesn't do much anyway, especially as American racetracks require little braking, referring to Board Track to Flat Track.. (I have a '54 Panhead that I've put a disc on as I got so close to crashing so many times) Even when Harley fitted the Massive brake calipers on a 10" disc and 5/8 bore master cylinders they were still dire! So there is proof size isn't important, a caliper off a truck and it still doesn't stop!
I suggest hydraulic drums were never popular on motorcycles due to the size of (available) components, (the industry will usually source what is available from sub contractors, ie Brembo) the complexity of a hydraulic system and bottom line, cost!

 

[highbury731]

Tim,
I think it is an option to use hydraulic drum brakes. The reason you don't see many hydraulic drum brakes on motorcycles is the the manual drum brake is so powerful.
David

A friend of mine converted his mid '50s Norton to hydraulic 2ls by using a brake plate off a car. The car, an early '60s Hillman, happened to be upside-down in his street being stripped. The plate went easily into the hub, a large nut happened to fit neatly as a spacer between brake plate and fork leg, and another fitted between plate and bearing area. He re-used the torque reaction lug from the Norton brake plate. A master cylinder was from a Yamaha he had scrapped a while before. The only expense was a brake hose to connect British brake plate fittings to metric master cylinder. It all worked a treat, excellent stopping.

I have heard of people using Mini 2ls brake cylinders and shoes to make their own hydraulic brake actuation. Owners have always reported being happy with results

Paul

 

[davidd]

The most powerful drum brake of all time is the duo-servo brake.

It was not a popular brake, but it is superior to double twin leading shoe brakes in performance. It is considered a single leading shoe brake by racing organizations. It is not very popular because it is wildly unstable, but if set up properly it will probably out-perform a big twin disc. This brake design was also used extensively in cars and hydraulically operated.

David

 

[passenger0_0]

The most powerful drum brake of all time is the duo-servo brake.

View attachment 21333
It was not a popular brake, but it is superior to double twin leading shoe brakes in performance. It is considered a single leading shoe brake by racing organizations. It is not very popular because it is wildly unstable, but if set up properly it will probably out-perform a big twin disc. This brake design was also used extensively in cars and hydraulically operated.

David

A Seeley front brake David?

 

[andrew peters]

The most powerful drum brake of all time is the duo-servo brake.

View attachment 21333
It was not a popular brake, but it is superior to double twin leading shoe brakes in performance. It is considered a single leading shoe brake by racing organizations. It is not very popular because it is wildly unstable, but if set up properly it will probably out-perform a big twin disc. This brake design was also used extensively in cars and hydraulically operated.

David

yes typical drum brake used on many cars and trucks from 1940s on.. complicated design, especially when 'miniaturized' for use on motorcycles, (read) expensive, less likely to be so viable for mass production compared to discs. Also heavy (reducing un-sprung weight more important on motorcycles than cars) and more maintenance than discs and more prone to heat fade. Cooling motorcycle brakes is not as easy as cars either, air scoops struggle to capture much cooling air as the front wheel is splitting airflow and deflecting air that that overheating little drum is craving. small drums get hot quicker than big drums. I'm really not convinced that any drum brake design even at its ultimate evolution can out-perform (in all practical situations) a disc brake (allowing the ultimate evolution of that design as well? ) imagine a wry smile at this comment please