Improving a 100cc front brake

[chris78jota]

The brakes on the tiddlers were fairly small by modern standards and started with single-sided drums which were held onto the right-hand fork leg by a through-bolt which passed through the drum and backplate - a basic steel drum on the 75, or an alloy finned version on the 100. These evolved into a full width aluminium brake on the Sport Lusso 100. The racers originally had something that looked like a larger-finned version of the 100, then a lovely full width brake.

Because I've nothing better to do with my time , and can't find a race brake, I've tried to improve a 100cc finned alloy brake as best I (and my mate the gifted engineer) can. The through-bolt can be a sloppy fit in the backplate and fork leg, so we've extended the unthreaded portion of its shaft and put a top-hat bush into the brake plate for a snug fit. The brake pivot has been bronze bushed ; it came with about 25thou clearance from the factory.

Classic Brake services relined the brake and skimmed the linings to a close fit.

In order to increase the finning and cooling, my engineer first skimmed the fins off the hub, then shrank a HE30 aluminium ring onto it. Five deep cooling fins were cut into it, as per the early single-sided race drum.
It'll be some time before I can try it out, but I'm hoping the alterations we've made will have maximised whatever potential the little brake has.

 

[sfcpiet]

Very nice job, Chris.

Tbh, I haven't found the front brakes to be lacking once decent linings are fitted and turned to size. In fact, I can imagine the (normally completely clapped-out) forks to be quickly overwhelmed by a decent working brake! I have a nice work-around for that, drop me a line for more info if you wish.

piet

 

[chris78jota]

Cheers Piet, I'll drop you a PM. I tried for ages to find Sport Lusso brakes like those but only found rears.

 

[Dellortoman]

OK, dumb question time. I know bugger-all about the tiddlers but I find them interesting.

I'm a little confused by "single-sided drums which were held onto the right-hand fork leg by a through-bolt which passed through the drum and backplate". The drum can't be fixed to the fork leg because it has to rotate. It's gotta be fixed to the wheel somehow. So I initially thought the backing plate was fixed to the right fork leg by a through bolt, separate from the axle, to carry the braking torque. But such a bolt couldn't pass through the drum as well. Now I'm reasonably sure that your use of the term "through-bolt" is another name for the axle.

How come there are no spoke flanges like those on the bike in the photo? I notice that the drum has a bunch of studs poking out of the back. Does the drum bolt onto the hub that carries the spokes, so the drum is actually outside the spokes?


Edit: Aha. Never mind answering my dumb questions. I just found a photo online. The brake drum is indeed bolted to the hub, outside the spokes.
From your photos above, it appears that the brake torque is carried by the lugs and the recess in the backing plate that the fork leg slots into.

1953 Laverda 75 Sport

Classic Italian Motorcycles of the 1950s Made in Breganze | Sheldon's EMU

cybermotorcycle.com

 

[Paul Marx]

OK, dumb question time. I know bugger-all about the tiddlers but I find them interesting.

I'm a little confused by "single-sided drums which were held onto the right-hand fork leg by a through-bolt which passed through the drum and backplate". The drum can't be fixed to the fork leg because it has to rotate. It's gotta be fixed to the wheel somehow. So I initially thought the backing plate was fixed to the right fork leg by a through bolt, separate from the axle, to carry the braking torque. But such a bolt couldn't pass through the drum as well. Now I'm reasonably sure that your use of the term "through-bolt" is another name for the axle.

How come there are no spoke flanges like those on the bike in the photo? I notice that the drum has a bunch of studs poking out of the back. Does the drum bolt onto the hub that carries the spokes, so the drum is actually outside the spokes?


Edit: Aha. Never mind answering my dumb questions. I just found a photo online. The brake drum is indeed bolted to the hub, outside the spokes.
From your photos above, it appears that the brake torque is carried by the lugs and the recess in the backing plate that the fork leg slots into.

1953 Laverda 75 Sport

Classic Italian Motorcycles of the 1950s Made in Breganze | Sheldon's EMU

cybermotorcycle.com

The brake drum is indeed bolted to the wheel hub. Theses drums are interchangeable front to back, and vice versa.
There's a sort of double axle for the wheel, the drum being mounted on a screw in mount through which passes the wheel spindle.
Paul

 

[sfcpiet]

The system is meant to keep the wheels interchangable, not necessarily the brakes. Rear drum incorporated the drive sprocket, that would look a bit out of place in the front... Perhaps it was meant for Luigi to keep a spare wheel at home back then, instead of repairing a flat tyre.

piet

 

[Paul Marx]

The system is meant to keep the wheels interchangable, not necessarily the brakes. Rear drum incorporated the drive sprocket, that would look a bit out of place in the front... Perhaps it was meant for Luigi to keep a spare wheel at home back then, instead of repairing a flat tyre.

piet

Yes, right.

 

[Sir Sidney Ruffdiamond]

A mile off but a thought , the cable was stretching on my Tiger cub front drum as well as the brake being worse than useless , I got a thicker cable made by JJ cables which has helped and the drum has got slightly better with use

 

[chris78jota]

A mile off but a thought , the cable was stretching on my Tiger cub front drum as well as the brake being worse than useless , I got a thicker cable made by JJ cables which has helped and the drum has got slightly better with use

Thanks Adam, not a mile off at all - a thick cable always helps. I bought a set from JJ (very helpful chaps) and I've also been experimenting with making my own from Venhill bits and pieces. The original levers and the adjuster locator on the backplate are fairly small diameter and limit things a bit, so I'm trying to find a balance between fairly original looking items and better performance. Piet is optimistic about the effect of well skimmed modern linings, so I'm happy that we're moving in the right direction with all this stuff. Going on a diet is probably an even better move

 

[DavidH]

Experience shows that having the drum skimmed when built into a complete wheel pays off, as does having the linings skimmed to suit the skimmed drum. Linings of course can be problematic, but here in AUS, people still working with motorcycle drum brake knowledge.
Wonderful work !

 

[sfcpiet]

Experience shows that having the drum skimmed when built into a complete wheel pays off, as does having the linings skimmed to suit the skimmed drum. Linings of course can be problematic, but here in AUS, people still working with motorcycle drum brake knowledge.
Wonderful work !

Lathes big enough to take a complete wheel are getting scarce too! There are other methods with which this can be achieved, but they all require quite a bit of skill and experience to pull off sucessfully.

piet