Britbike forum Forums British motorcycles in general Bsa gold star forum 8" single sided brake drum material

I seem to be taking over the forum at the moment! Just focussing on prep for various jobs I want to get done over the Winterval..

Right... 8" (& 7" for that matter) Single sided Goldie / B31-33 brake drum;
What material/s are they made from? Steel? Cast iron?

I know for certain that the various rear QD type 7" chainwheel drums can be found in both cast iron & steel.
I have never seen a broken or bent front drum to have got any idea of material

HA! looking in Roy Bacon's Singles restoration book I found reference to them being cast iron. It is what I thought but just I couldn't recall ever having read that before (which I must have, it's a well thumbed copy) or anywhere else. Brain fade.

I'm actually looking at drilling an 8" drum for racing but didn't want to end up scrapping the drum by making it weak. Obv. the later GS drums are well drilled already which should set anyone's mind at rest.

Hi Flowboy
The 8in. front drums were made in both steel and cast
The easy way to tell is the plain drums without fins or cooling/ lightening holes are steel
The finned cast hubs came with two different depth brake drums, the difference is inside the spoke flanges
The deep drums were AFAIK from the A65

John

Hi Chater'

Thanks, I didn't know they were in both materials. I've never had reason to try drilling or lightening a front before where I might have found out.
If asked I would have said the GS type with holes & Welch plugs would have been steel & the plain ones cast iron. That's only based on someone years ago, telling me to find a steel rear chainwheel hub if I was going to drill it full of holes, as the cast ones were brittle & might fail. I have no idea if they are really brittle or what type of cast they are.

I've often seen the A65 brake described as GS - it is very similar but the GS is shallower at the back. The A65 does have a bigger pad / shoe area which is a good thing in traffic or on the track. I do know the finned ones of either sort can be expensive...

There were, AFAIK, 3 different width 1/2 width brake drums

1.375” - very early 1/2 width

1.500” - most common thru 1965

1.625” - 1966 -1970. All Twins, 66 - 67. Single carb Twins, 1968, B44 68 - 70. These are not bad brakes. They actually perform decent with good lining and set up

My race bike had the un-finned Goldie vented drum. If set up well it's a pretty good brake, altho' it helps to have a good cable & strong right hand! They do get hot (enough to get the paint peeling) & fade a bit on track. On a 350 it's not so bad, a 500 would be harder on one so I expect the finned post '66 version would be an improvement. My Road DBD (un-finned 8") doesn't stop on a sixpence that's for sure, even with 2LS brake plate. That said, it is quite a bit heavier than a race bike.