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Twin leading shoe benefits?

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Alex jb

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Discussion Starter · #1 ·
So the CD175 has a single lever/cam action


Where as the CB/CL has the twin leading shoe action


So my question is, any of you guys used both and can tell me the benefits in braking power?

I am planning on a wheel re-build at some point and wondered if it it worth sourcing the CB/CL system.
I know the torque reaction arm is different also, that can be accommodated fairly easily.


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B

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#2 ·
Find a CB brake panel. Properly set up both shoes work with the effort you put into the lever pull. The CD brakes would require far more effort to match the CB braking power as one of the shoes will be working against the cam action. Really a no brainer unless you are doing a correct restoration.

When you set up a twin leading panel do it so the cam furthest from the pull lever contacts the drum slightly before the other. Takes a little back and forth but it is worth the effort. Also note that the cams are location specific ....
 
ancientdad

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#3 ·
Yes, the twin leading shoe is far superior to a single leading shoe brake because the leading section of the brake shoe - the end best suited for leverage against the drum - is far more powerful than the trailing end and with both shoes working the leading end of the shoe as opposed to one leading end and one trailing end in the single setup, the braking power is significantly better. Any high-performance bike on the road before disc brakes had a twin leading shoe front brake, and the road racers of the day often had double-sided twin leading shoe panels with a total of 4 leading shoes, stopping as well as a disc except for the given fade of a shoe brake under repeated use in any era.
 
83XLX

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#4 ·
Good info. I'll add that while a DLS front brake stops much better than a comparable-size SLS going forward, they work much worse when rolling backward, so take that into account if you're ever stopped on a steep uphill or are backing the bike down a ramp.
 
ancientdad

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#5 ·
83XLX said:
Good info. I'll add that while a DLS front brake stops much better than a comparable-size SLS going forward, they work much worse when rolling backward, so take that into account if you're ever stopped on a steep uphill or are backing the bike down a ramp.
Click to expand...
Valid point... good thing where I am is pretty much flat everywhere! Unlike where you are, which is why that never crossed my mind. :D
 
Alex jb

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Discussion Starter · #6 ·
Good info, thanks fellas.

We sketched it out in the white board at lunch time (room full of engineers can't help themselves) and we figured it was contact area as the SLS brake only pushes one side of the shoe and the effective lever arm from the non pushing pivot is much longer.



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R

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#8 · (Edited)
It's called 'self servo action', plenty of info via Google.

Engineering Inspiration - The Geometry of Drum Brakes

I can confirm that 2LS brakes don't work very well going backwards.

My drum braked BL Mini 1000 had twin leading shoe front brakes as standard. Brakes required drums to be removed at frequent intervals to empty out the brake dust, then adjusted using a special spanner on the two adjusters on each brake plate. These adjusters regularly seized if not kept clean and lightly lubed. Happy days, not, grovelling under cars in the cold and wet does not appeal any more.

Anyway, to the point. Showing off in the Mini, reversing at high speed, four up, just managed to stop the thing before toppling into a ditch. Not that the brakes were that good going forwards ..
 
Alex jb

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Discussion Starter · #9 ·
Ok, I'm getting closer to convinced :)
Providing the shoes are the same diameter (140mm I think) I can get a hub and figure out the cable and torque reaction arm.


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Simo

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#10 · (Edited)
First up you cant just swap the plate, the cd has a 140mm sls drum, the cb is tls 160mm.
Ive always liked this
Drum Brakes Compared by Method
There are a few other differences in the cd and the cb front end set up.
The cd forks are set wider by 8-10mm, you can easily fit a cb350 drum into cb175 forks and there are other hub options as well. Ive got a T500 front hub I eventually want to put on my CD175

Personaly I wouldnt worry about the directional brakeing issue of rolling backwards as the rear drum is Single leading edge, and youre upping the size of the front brake from 140mm sls to 160mm tls (cb175) or 180mm tls (cb350)
 
Alex jb

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Discussion Starter · #16 ·
I have my eye on a cb350 180mm front as I can build the wheel in parallel with the engine.
The XL350 has a large dia drum, but back to sls and not sure how the speedo drive will work out.


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Simo
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