Norton SLS - 2LS conversion

[Teedee]

Right, here's one that might have been asked a dozen times (but I couldn't find it) or it's something nobody has given any thought to. Could I be right that a Norton SLS brake with removable pivot point can be converted to 2LS by changing said pivot for a cam?

As I've never seen it done before, there must be something really stupid I'm not thinking of. But I can't come up with why it shouldn't work.

The only thing I would consider is beefing up the area around the pivot point/future cam.

Cheers!

Tim

 

[Triton Thrasher]

How/where where will you pivot the trailing end of the former trailing shoe?

 

[Teedee]

Good point TT.

By converting the cam with a 'half moon' on one side to make it act as a pivot on that side?

(credit: https://victorylibrary.com/brit/SLS-TLS-c.htm)

Or by getting cams from a 2LS

The theory is there, but I'm a bit apprehensive of theory only. The internet is full of theories. Does anyone have actual experience with this conversion?

Cheers,

Tim

 

[acotrel]

Dangerous. If it locks at speed, you might go straight over the front.

 

[Schwany]

Don't need to be an engineer to know that would not result in a 2LS brake. Being apprehensive is the correct reaction.

Having real world experience from commenters is a big ask in a forum.

 

[Teedee]

Having real world experience from commenters is a big ask in a forum.

One can hope... Weirder stuff happens in the world.
I'm not an engineer, and still fail to see why it shouldn't work. Can you explain?

 

[mdt-son]

You can do that, provided the boss for the second expander cam is reinforced. You need a different kind of brake shoe of course. They can be left free floating, using a simple guiding system as per 70's cars which had twin hydraulic cylinders (e.g. Morris Marina). Numerous car models of that era used free floating brake shoes. They align as soon as pressure top and bottom is applied, increasing the friction area up to 50%. Braking force is transmitted via the expander cams.

If you want even better brakes, you can go all the way converting your brake plate to twin hydraulic cylinder operation. It's unobtrusive and works much better than a mechanically operated drum brake.

- Knut

 

[Schwany]

One can hope... Weirder stuff happens in the world.
I'm not an engineer, and still fail to see why it shouldn't work. Can you explain?

Busted!! No not in anyway that would pass a mandatory interweb technology test. It looks Rub Goldberg to me is all I've got.

I'd use my wallet and get a 2LS brake. Done

Try it. It would be interesting to know if it works. And being wrong is my specialty.

 

[Teedee]

Haha, I appreciate your honesty Schwany.

Using a wallet isn't always possible. Sometimes financially, sometimes because the parts needed just aren't to be found and sometimes out of the convincion that if you just pay, instead of doing it the hard way, you'll never learn. For me, it's the last two, with a bit of the first when I see what people dare to ask.

And thanks Knut. I'll have a look at the Morris Marina system to get an idea. Going hydraulic isn't an option, as there are certain regulations regarding period parts to be met. Would be interesting though, but I fear my spannering qualities are at a stretch already by trying this conversion.

Doesn't stop me from trying though. Even if you try and fail, you'll have learned something. And no worries, if I do try, I won't just immediately ride it in anger to then see it fail.

Tim

 

[acotrel]

Even a single disc is superior to any drum brake.

 

[acotrel]

When you use the drum front brake on a motorcycle, it usually heats-up and changes. The linings can either fade, or they can become sticky. In a TLS drum brake, one end of each shoe is usually on a pivot - the other ends are moved by the cams. If both ends of both shoes float, the brake becomes particularly dangerous. It can work OK when cold, but unreliable when hot. I have been chucked over the front of a bike about 4 times at high speed. Never when using a disc brake - they are much safer - and cheaper, Probably the best drum brake is an Oldani - big money !

 

[baz]

When you use the drum front brake on a motorcycle, it usually heats-up and changes. The linings can either fade, or they can become sticky. In a TLS drum brake, one end of each shoe is usually on a pivot - the other ends are moved by the cams. If both ends of both shoes float, the brake becomes particularly dangerous. It can work OK when cold, but unreliable when hot. I have been chucked over the front of a bike about 4 times at high speed. Never when using a disc brake - they are much safer - and cheaper, Probably the best drum brake is an Oldani - big money !

Ok Al I'll bite (pun intended) what do you say about the millions of "ROAD MILES" that people cover successfully using drum brakes?

 

[Teedee]

I've had the disk brake of a Buell once heating up so badly on track, that I could squeeze the lever all the way to the grip after the long straight. Scary moment...

After a massive tank slapper on an MuZ SkorpIon at Assen, I found myself pumping the front brake like a maniac, trying to get the brake pads near the disk again after the slapper pushed them all the way back. Another scary moment...

What I'm trying to say is that every system has its own weak points.

I'm aware of the superiority of disks, but drums are not as bad as people think, if properly set up. It's just a different feel.

 

[Triton Thrasher]

Good point TT.

By converting the cam with a 'half moon' on one side to make it act as a pivot on that side?

(credit: https://victorylibrary.com/brit/SLS-TLS-c.htm)

Filing/machining one lobe off the cam, down to a radius, makes more sense to me than adding lumps of metal.

However, Acotrel has a point. If you mess around with self-servo geometries, it is possible to make a brake that jams itself on and throws you off the bike.

 

[mdt-son]

If both ends of both shoes float, the brake becomes particularly dangerous. It can work OK when cold, but unreliable when hot.

This is not an argument, it's a prejudice. Floating brake shoes were used in cars for years before disc brakes became commonplace. The self-servo effect isn't any larger than for a TLS brake, but the non-energized quarter shoe becomes more effective. A TLS brake is approximately 1.5 times more effective than a similarly designed SLS brake. Floating brake shoes gives an even larger advantage.

Drum brakes are not "unreliable" when hot. Agreed, the perceived friction force is reduced, but so does a disc brake when hydraulic pressure is kept constant.

Brakes may become dangerous if the brake pad bond to the carrier or shoe is lost. If this happens, the brake pad may form a wedge and the brake may lock up. Even though energized brakes (SLS or TLS) may be grabby, the braking effect is released by easing the cam or slave cylinder pressure. If braking threw you over the handlebar, either you lost your head, or you experienced a mechanical failure!

- Knut

 

[Chris]

Hi Tim
I have a photo on my old computer of a Degans conversion. Internal! As you could not alter the outward appearance. Lol I will try & dig it out.

 

[mdt-son]

Victory Library model realized as can be seen by my countryman Arne Eriksen for an AJS bike (7" brake). Concept proven!

- Knut

 

[Schwany]

Looking at the drawing and reading the text in the drawing I got the impression it was only 1 cam, which would make it ridiculous. Making the linkage and modifying the backing plate for two cams wasn't mentioned. I thought there was some magic being applied, which would never work.

 

[Triton Thrasher]

Victory Library model realized as can be seen by my countryman Arne Eriksen for an AJS bike (7" brake). Concept proven!

- Knut

Is that collar just sitting there, between the lever and the backplate?

This doesn’t look as strong as the original two pivot pins through the backplate, with the fishplate across them.

The original single leader shoe pivots:

 

[mdt-son]

Is that collar just sitting there, between the lever and the backplate?

TT, I appreciate your interest and your criticism. First of all, I have not been involved in this project and can't tell you about the details. I can send you the originator's contact information, if you want to discuss with him.

The "collar" should form a boss, as an integral part of the brake plate. I don't think a threaded boss which screws into the brake plate will be stiff enough. A pressed solution may work.

The pivot pin (which is now the brake cam) needs to transfer the shear force of one energized brake shoe and the resulting bending moment, both acting on the foundation which is the brake plate. In the present design, the single pin needs to be of rugged design. To prevent tilting, it needs to be supported in a rather long boss

There is no ready-made solution for Norton's SLS brake plate. Anyone embarking on such a project must do his own calculations to make sure the solution is roadworthy,

- Knut