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Improving original drum brakes

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Post Mon Apr 19, 2010 8:26 am

Have a nice day.
Last edited by panic on Tue Apr 20, 2010 11:09 am, edited 1 time in total.

Post Mon Apr 19, 2010 2:01 pm

Posts: 575
Location: devon,england
hi panic ,i like the thinking and the relative ease of the method and costs involved and as only the shoes are altered beyond returning to standard its got to be tried.
regards jib :D
Dude, check out that jibhead, he's crazy. Hasn't been sober for 40 years

Post Mon Apr 19, 2010 3:55 pm

Posts: 159
Alternately just shave off 1 1/2 inches off the trailing shoe at the cam end. It's been tried on a million Pommie bikes with success.

Post Mon Apr 19, 2010 8:57 pm

Last edited by panic on Sun Nov 28, 2010 5:50 pm, edited 1 time in total.

Post Tue Apr 20, 2010 5:26 am

Posts: 304
Location: oklahoma usa
I don't get that one either.

Post Tue Apr 20, 2010 6:20 am

Posts: 11
Location: The Netherlands
The duo-servo solution as used in car brakes can not be applied to cam-operated motorcycle brakes. In hydraulic car brakes the shoes are self centering, they do not have to pivot on an anchor pin. In a cam-operated brake the cam tends to move the shoes not only in a horizontal plane (assuming the cam is at 12 o'clock), but also in a vertical plane. Without an anchor pin the shoes will then drag upon releasing.
The shaving of lining from the trailing shoe lowers the friction between that shoe and the drum and hence the pressure of the trailing shoe on the cam, so more pressure of the cam is directed towards the leading shoe. Remember: the trailing shoe is hardly adding braking power, it is just consuming cam pressure (hence the TLS solution). In practice, HD brakes are so under-dimensioned that applying more pressure to the leading shoe does not increase braking much (at a certain moment the braking action of a lining does not increase any more with the pressure from the cam). I have tried this shaving myself, but it was fruitless.

Post Tue Apr 20, 2010 9:30 am

Posts: 90
Location: Norway what makes the hydraulic brakes self-sentering? Will it be possible to adapt it to cam-brakes?

I was thinking of this: Shorten the shoes in the cam-end (might need some welding). Then make the anchor-pin rectangular. The box will not be able to rotate in this manner. Then you modify the box to have 1/2" round shape to fit the shape of the shoes. A small spring could be added to positivly move the box to the left when the brake is released.

Another thaught: moderrn air-operated truck brakes uses cams. Is there any theory to learn from them?

Post Tue Apr 20, 2010 9:40 am

Posts: 1604
I really wouldn't bother with any of this. The stock H-D drum brakes, both springer and 'glide type, are so under-specified that nothing you do will ever make them work as they need to. They are too small, the drums are not sufficiently robust, in the case of the 'glide type the actuating arm is at an obtuse angle to the cable and the bent tube in the cable run doesn't help, either.

The 45 depot 2LS conversion works better than the stock unit, which isn't really saying much. Overheating, fade and brake drum distortion are the limiting factors.

If you want reasonable brakes with a period look, ditch the stock wheels and use a BSA or Honda 8" SLS or 2LS drum. Various threads on that on here already. If you want as much braking power as the springer fork will be able to handle, use a single disc. Plenty of details on here for that, too. If you want a stock appearance, learn to live with the crappy brakes.
Shoot, a man could have a good weekend in Dallas with all that stuff...

Post Tue Apr 20, 2010 4:24 pm

Posts: 159
Taking off material from trailing edge allows leading edge to touch first and wedge into drum for self servo effect. It's been proven. Have a look at early single slave cylinder setups on car drum brake setups. I've done carbrakes at a garage for 30 years with all sorts of configurations.

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