Swarfy yes that extra arm is between ugly and strange but with split pins should it be scary? Ie, dangerous? I made it as I didn't want to mod and solder the brake cable etc.
I might try marking the drum and shoes with pen/pencil to see how much contact is actually occurring. Any tips on suitable markers that won't then affect the friction surfaces?
Hi Mike, maybe we’ll be discussing this at the National Rally in a few weeks! I agree with previous comment that it’s worth REALLY making sure the leading shoe contacts first, by adding a temp spacer, or building up the cam face by weld I did. I’ve had good feedback from other riders of my B31 on the front brake as “much better than mine
”. Including from a gold star owner. It will lock the wheel at slow speeds but is a lighter bike of course.
Its accepted pretty generally that more than 75% of your braking comes from the leading shoe (due to the servo effect) so IMHO that’s what one needs to concentrate on, one thing is I’ve not put much thought into is the effect of reducing the leading shoes contact length, maybe this can increase the servo effect? Is it worth trying? (Noting this reduces lining contact area, but increases pressure on the lining).
My gut feel is that removing the part of the friction lining on the leading shoe, nearest the cam, would increase the servo effect? Can someone confirm that? I’m thinking you need to get closer to the “brake grabbing” effect....albeit if you don’t like that effect you may have to get new shoes....as you can’t replace removed friction material!
I note trailing shoes can also have shoes with reduced lining length, I’m not sure why but probably to try to prevent them wearing in a way that prevents the leading shoe working properly, as there is no significant servo effect on trailing shoes.
Another “variable” is the chamfer on the lining, is the servo effect increased with no chamfer? Anyone know? ( I suspect it’s reduced, as no chamfer can cause bad grabbing).
On lining contact area maximising, it appears trying to get an even contact might be a good thing to do but more a “nice to have” ...I say that as sanding the shoes to get perfect contact only made only a small difference to my brake (albeit it reduced the “sponginess” a great deal), and “physics” says friction is proportional to contact area and pressure so if you increase the area you reduce the pressure and maybe end up no further forward
. I definitely see advantages in spreading the generated heat over the whole friction lining though, as local overheating of the lining may result in a low friction co efficient. Getting the brake to work well is not simple physics though, as shoes flex, linings compress, brake plates flex, drums flex, all of which affects the evenness of force over the lining, probably making it a bit of a “black art”. A SLS brake is inherently “flawed” as one end moves more than the other!
Accepted wisdom around here is that “soft” linings work best on our brakes, and that modern linings are “hard” to suit higher pressures from hydraulic pistons. I’ve no direct experience of this but I suspect some wassel aftermarket bonded shoes I bought are “hard” hence that’s the cause of my useless rear brake (as well as them being too small in diameter, and so thin sanding them to the correct diameter would make them virtually worn out!).
It’s also occurred to that a old school brake specialist would know how to set up a SLS brake to work well, and make the customer happy, but maybe as the linings wear the trailing shoe gradually comes more into contact and reduces the brakes performance, and the specialists knows that!
