Can i increase the stopping power of my rear drum brake by.....

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cycle tramp
Posts: 475
Joined: 5 Aug 2009, 7:22pm

Can i increase the stopping power of my rear drum brake by.....

Postby cycle tramp » 9 Feb 2019, 10:40pm

Can i increase the stopping power of my SA 70 mms rear drum brake by increasing the length of the brake arm, from pivot to cable anchor point?

Brucey
Posts: 32274
Joined: 4 Jan 2012, 6:25pm

Re: Can i increase the stopping power of my rear drum brake by.....

Postby Brucey » 10 Feb 2019, 12:51am

yes, why not. However eventually you run out of lever travel/cable pull. Daft question; you are using high MA levers? I.e. ones that are not meant for V brakes?

Do check that the cable is well-lubricated. if you are using the pre-made SA cable this will benefit from being lubricated properly. This is best achieved using a hydraulic lubricator (as is used for motorcycle cables).

The other thing that makes a big difference is how the brake plate is installed. There are two issues;

1) concentricity (here a floating brake or semi-floating brake plate helps) and
2) skewness.

Skewness? -in a front brake if the brake arm is sprung into position you can't expect it to go back in exactly the same place each time the wheel is disturbed, and if the angle changes even fractionally the brake loses power until it is bedded in again. The same is true of the rear wheel too. On several occasions I have refitted the rear wheel in a bike with a SA hub brake only to find that there is a change in the brake performance. In hindsight this has usually come from the way the wheel straightness/chainstay fitting interferes with the exact angle of the brake plate.

The slightest strain on it and it sits slightly skew and the brake doesn't work so well any more. In the future I am probably going to revise the fitting onto the chainstay so that the wheel/brake plate isn't so likely to sit at a funny angle. In the meantime I am going to be extra-careful that the chainstay fitting isn't in any way strained when it is tightened.

Other things that probably make a difference include

- which way the cam is turned; it is possible that the rear brake might work slightly better if the cam is turned ACW (like the front brake) rather than CW (like the rear brake).

- if the brake shoes are feathered at the ends

- if there isn't too much brake dust in the drum assy.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

rjb
Posts: 3058
Joined: 11 Jan 2007, 10:25am
Location: Somerset (originally 60/70's Plymouth)

Re: Can i increase the stopping power of my rear drum brake by.....

Postby rjb » 10 Feb 2019, 8:21am

It may be worth trying some "servo wave" brake levers with variable geometry. You will probably need to look on flebay from these nowadays. :wink:
At the last count:- Focus Variado, Peugeot 531 pro, Dawes Discovery Tandem, 2 Dawes Kingpins, Raleigh 20, Falcon K2 MTB dropped bar tourer, On One Pompino, Longstaff trike conversion on a Falcon corsa. :D