Improving SLS brake.

There are a few conundrums...

Norton drum brakes are cam operated, and the tails of the shoes have their own anchor pins so they do not float together.  This means that, as they operate and as they wear, both the shoes must always move exactly the same amount.  So they must wear at exactly the same rate.  So they must both apply the same force, and so the leading and trailing shoes must do exactly the same amount of work.  (The force from the cam onto the leading shoe would be smaller than on the trailing shoe, because of the servo effect.)

If they had hydraulic brakes, each shoe would receive the same force (not displacement), so the leading shoe would be able to apply more force on the drum because of the servo effect.  So that would provide a better brake.  Obviously in that case it wouldn't help to remove any area.

Wasn't there a fashion to add Mini hydraulic cylinders to drum braked bikes at one time?  I used to assume the benefit was in zero cable friction, but actually it must also because both shoes are able to work to maximum effect and the trailing shoe doesn't restrict the action of the leading shoe.

I'm pretty sure Wikipedia has articles about this.

It is true that both SLS shoes must wear at the same rate in a Norton brake with fixed pivots.

As the leading shoe has a self-servo action, less force is required to turn the lobe of the cam operating that leading shoe. Therefore the riders effort is biased to turning the operating lobe of the trailing shoe.

In a TLS setup the cams can be setup to have less leverage, because the mechanical advantage required is less, so less cable travel is required for the same braking effect. Or alternatively there can be more force pushing the linings into the drum (adding the self-servo action) when applying the same mechanical advantage.

With a sliding slave hydraulic cylinder setup, you should get more wear on the leading shoe. But I cannot remember ever having noticed that in practice.

I just bought a pair of TLS shoes from the club to get relined at Villiers Services. As part of my lifetime quest for brakes that grab.

... to be considered is that as the cam is symmetrical the inner end moves the corresponding shoe further than the outer as it's working on a smaller effective distance. Correspondingly there is more force applied at the other end of the cam ie on the other shoe.

This effect means that setups where the operating lever opposes the rotation of the wheel give more travel but less force applied to the leading shoe and the converse where the arm follows the rotation of the wheel as on my ES2.

This effect obviously diminishes as the linings wear.

Ian...help!

As you say...so as the cam moves, it pushes one shoe very slightly more distance than the other. Whichever shoe is pushed further must wear quicker or they wouldn't both stay in contact with the drum. If it is the leading shoe, that shoe can do more work than the trailing shoe, which is what it tries to anyway because of self servo effect. If it is the trailing shoe, then that is being forced to try to do more work, which it is not good at doing. So the brake will work less well. Now to check the 16H ( with left hand side brake) and Inter (with right side brake). I see in both cases the lever turns the cam in the same direction as the wheel turns. So the leading shoe is indeed being pushed a little further than the trailing shoe. 

Meanwhile the Inter has a larger front wheel. That means a less effective brake, because the road friction has a bigger mechanical advantage. Unless that is countered by different lever lengths?

I'm going for a ride. On a Tls Dommie.

Robert, I removed 40% of the trailing shoe friction material on the trailing end. The improvement was quite noticeable. I have my own theories as to why this works expressed on this forum in the past.

I just use push on Tecalemit gun with a piece of cloth over the nipple to prevent leaks..on the footwear and similar simple grease nipples. I've never dared use one on the brake cam...

Robert,

You mentioned you use a HMP grease, but what type?  Having found in a work application that a specified wide temperature range Aeroshell grease would turn to a white powder when exposed to the high temperature working environment, a change was made to a modern Fomblin type grease, which eliminated the issue completely. This grease is versatile, can withstand high temperatures and has good water resistance properties, so would seem ideal for the brake cam spindles.  The only caution would be that it does not react well  with other greases, so everything would need to be fully cleaned prior to application.

An option for you anyway.

Andy

.. for this application as there is relative motion between the cam face and shoes as well as between the cam spindle and bush albeit to a small degree in both cases. I've always found a thin smear of HMP lithium grease works better than anything.

Copaslip is not intended for this type of use but is an anti-seize compound.

Thanks for the warning Ian.  I have silicone grease...looks like it might be suitable.

Year and model of bike???

  If you are not hung up on originality, can you not try to find a twin leading shoe brake plate at a flea market or auto jumble?  It will fit right in with no modifications except maybe for the change in cable.

... not sure what you mean by silicone grease - what I understand by that is the anti-corrosion grease used on electrical contacts etc. Something like this would be ideal in my view: