If you lengthen the arm, you change the lever ratio between input (clevis in bottom of middle photo) and output.

That ratio change will persist along the operating rod and be seen by the other input to the drum.

It would be prudent to make sure that you have taken this into account before doing any modification.

Is there any reason the operating rod cannot have a joggle in it to snake its way past the obstruction? As long as you maintain the straight line (crow flies) distance between the two parts to which the rod is connected, the shape of the rod (providing it maintains sufficient compressive stiffness) does not matter too much.

If you lengthen one, you will also have to lengthen the lever for the other brake shoe to match,otherwise there will be uneven braking force on the brake shoes and uneven wear. Brazing would be effective, but you should have the old plating stripped off first. The chrome platers can do the stripping for you, chemically. How did all the riders of Japanese bikes and the British bikes just before discs came out cope with twin leading shoe brakes on hill stops?

What Honda did the 180mm brakeplate come from?

Edited By old mart on 13/05/2023 19:53:59

I would use a butt weld rather than brazing. For critical safety items like that I take it to a professional and get it TIG welded. I don't trust my life to my own bird-droppings welding skills. Recently on shortening a Norton brake pedal for rearsets, the welder at my local light aircraft field did a lovely job of it in return for a few beer tokens.

In the 60’s I had a brake stay part company with the aluminium fork slider on a Matchless G80, it smashed the fork slider but fortunately the bike was coupled to a sidecar at the time which meant that the machine stayed upright and came to a stop, the consequences could have been serious had the bike been solo. Great care is needed with anything to do with braking systems. Dave W

The reason I wondered about the 180mm drum size, was that the CB72/77, the 450 and the sports Benleys had 200mm brakes. Perhaps the CB175 had the 180. Everybody seemed to make TLS brake plates for the Norton/AMC 8 inch full width hub, and at least one make for Velocette, but not the AJS/Matchless 7 inch hub.

Since the op has not finished the brake, who can be sure it will not work?

The earliest 2LS brakes on motorcycles had the linkage within the drum – on the inside of the brake plate. I think this was mainly on racers and perhaps a way of avoiding questions from scrutineers etc.

And I can be fairly sure it won't work backwards, whatever is done with the linkage.

Just before disc brakes become de-rigeur, even on mopeds, there were one or two systems where the brake cams could float, allowing the shoes to slide and giving a 'leading shoe effect' in both directions. BSA had this about three days before they went down the plug-hole.

Oh happy days …

Cheers, Tim

TLS brakes do work when going backwards; just not as effectively, for the same force applied to the operating lever.

In any drum brake set up, trhe leading shoe self servos, to apply more force to apply the brake. In the same tway, the trailing shoe self servos towards OFF rather than ON.

When moving backwards, the "leading" shoe, becomes effectively a trailing shoe, and the "trailing" shoe becomes leading. In this way the brake is as effectiove when applied in either direction.

TLS brakes will be more effective, going forwards, but less effectgive in reverse, but thay still work, merely requiring more lever or pedal effort to deliver the same braking effect.

Howard