Single leading / trailing drum brake cams.

J. M. Leadbeater

Joined
Apr 21, 2015
Messages
322
Was asked thequestion why are they different shapes? Going from memory/ wiithout climbing into the loft to drag out the box containing them......the front one is oval whereas the rear is flat sided. Anyone know why Norton did this? I seem to remember the twin leader cams were shaped as the old rears......
 
Flat sided anything is always less expensive to manufacture, especially before CNC.

Slick
 
A good drum can be amazingly good. I imagine many people underestimate this.

I raced with a new replica magnesium 4ls that I swear was at least as good as the eligible disc brake options. It was incredibly powerful, had tremendous feel, and had a tangible 'self servo' effect as the shoes were 'pulled' into the drum under hard braking. The only downside was it required frequent, careful adjustment to keep it so.

However, that brake was never as good when I had it re-lined, despite using a proper professional outfit to do so, and despite trying several different linings.

I also had an exotic 8ls front drum that despite spending large sums of money on, even despite finding and using some original AM4 lining material, I could never get to work as well as it should (or well enough to justify its weight)!

My conclusion: drum science, including lining material, lining to drum relationship, and cam design is complex, and way beyond me. Hence I'm now a disc guy!!
 
J. M. Leadbeater said:
Was asked thequestion why are they different shapes? Going from memory/ wiithout climbing into the loft to drag out the box containing them......the front one is oval whereas the rear is flat sided. Anyone know why Norton did this? I seem to remember the twin leader cams were shaped as the old rears......
Click to expand...
Triton Thrasher said:
The rear brake was a bit crappy and cheap-looking, generally.
Click to expand...

The flats not being oval on both sides is a new one to me, definitely something wrong here as you can mount the pivot pin either way in the brake drum :!:

I had my drum brake shoes relined by Joe Dunphy when he supplied oversized Ferodo brake shoes and skimmed down to fit the drums- they were excellent brakes both front and rear and was well worth the money at the time :)

This is done with OVERSIZE brake lining riveted on to the shoes, then the brake drum is fitted onto a mandrel and .020” shims on each brake drum flat and skimmed down on a lathe to the exact diameter of the brake drum, the .020” shims are removed and a 30 degree chamfer filed onto each leading shoe.
 
Norton employed a single leading / trailing brake with a pivot on each shoe at one end togeter to each other and the single brake cam at the other end which operated both shoes. I have a pile of std Nortons leading trailing brake cams and the box contains both types. I suspect that the two types give a different feel to the engagement characteristics . Just thought there might possibly be someone out there who would know the thinking behind each type........
 
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