Vented rear drum brake

The method used in the Norton factory 2LS kit can be faked with a lot of work. The hard part is manufacturing the cam and pivot with studs on top to mount the stiffening ring.
I can't compare the alloy plate, except to comment that when many of these parts were designed (50 years ago) the weight diff was the only consideration (and it's unsprung).
How much stiffness was need for function was simply not understood, and aluminum is far more flexible than steel for the same cross-section - an alloy plate has to be 3 times as thick to have even the same effect: Young's Modulus: aluminum 10, steel 30 (* 10^6), and you have no weight saving at all. If you increase stiffness by 50% (which may not be enough if you can see it bend) it must be 450% as thick and 50% heavier (although some structural shape changes can help here).
They made the same mistake with pushrods...

If you have some pics of the plate, we may be able to figure out where it can be improved with minimal work, min weight gain and min cost?

I've seen the stiffening kit work wonders on the Norton TLS front brake. My experience of a Fastback without this mod was frightening.

Yes, I'm aware that aluminium would have to be much thicker than steel to resist bending. The 70s Ducati single drum brake had a large boss cast on the exterior, extending from the lever pivot to the axle and then to the brake anchor point. That rear brake was very effective and the design could be used for a one-off.

Your offer of help is much appreciated, and I'd be interested to see how the standard brake plate could be stiffened. I've just put the old girl back together so I can go for a spin at the weekend, so when I have the wheel apart again (and that could be soon), I'll take some pics and send them to you.

Ludwig — that's impressive. You said that you can use Mini brake shoes and VW slave cylinders. Where does the brake plate come from? Even though it would be an interesting adventure, I'm not sure I could face all the work involved.

You made a very good point about the offset of the brake lever. I noticed this today as I watched the brake plate bending. My rod operated system has a bit more of an offset than standard, so no doubt that is not helping matters.

Thanks for your post and pic.

ludwig said:

, only a part of the force applied on the brake pedal is actually used for spreading the brake shoes . The rest only wants to warp the back plate

Click to expand...

You mean standing on the brake pedal doesn't help? How about praying?

Yet another interesting innovation on your Norton, nice work!

Ludwig is that the rabbit slave cylinder we are seeing here? And if so witch size?

If you do straighten your brake plate , mount it off the centre as it would on the bike but get it so that the shoes run straight,what are the chances that the longer brake arm with more offset for your rod set up is just going to twist the flimsy little plate evey time

Splatt — the amount of offset of the lever is a key point that I overlooked when I made the rod set up. Ludwig designed his set up to avoid this. I do have some room to reduce the offset. I have straightened the plate as much as I can and I will check that the shoes run straight when I get new ones.

Hi there, i had seen somewhere that some prefear to use the Atlas rear backplate as the lever pivot had a longer/better support /shoulder, but need to change the peg which slots into swingarm,,,,,,,,maybe help anti-
wrapping effect????

Daveh,did you have any luck getting you brake to work,or is it still a form of abs.

Splatt — thanks for your interest. I managed to straighten the brake plate, as you know, but I also discovered that the edge of the plate itself was touching the inside of the swinging arm fork when the axle nut was tightened. I had fitted a new chain, and the axle was very close to the front part of the slot in the swinging arm lug. When the axle was tightened, it cocked the brake plate slightly because the inside of the swinging arm tube was pushing it inwards. A small shim on the dummy axle cured that. The chain and sprockets are now perfectly aligned, which was not the case before, and I couldn't see why. I only spotted it when the chainguard was removed.

But, the brake is still not great, even though the shoes are now making full contact with the drum. I reckon it is suffering from fade. I will try some shoes with harder brake material (as sold by RGM) and report back!

Dave

Ludwig — you posted a photo of your rear wheel on another site. Very neat. Do you mind me asking you from which model the rear wheel and caliper originate? Did you fit a larger diameter wheel spindle (e.g. 17 mm) and widen the slots in the swinging arm lugs? And finally, where is your speedo drive, or do you have a bicycle speedo?

Dave