I’ve been recommissioning a 1974 850 Mk2a Interstate. The bike hadn’t been used for a number of years so I’ve given it a thorough service and a good going over. With a break in the weather last we I took her out on the road for the first time. One thing I noticed was excessive movement of the rear brake pedal to get any effective braking (about 2.5”). Back in the workshop I adjusted the pedal to give a more reasonable amount of movement but then found the brake to be binding. It’s was as though the first half of the pedal movement put the brakes shoes into contact with the brake drum and then the second half of the movement applied the brakes proper.
I dismantled the brake drum/ sprocket and inspected the brakes. The shoes look nearly brand new and seem to operate correctly. Suspecting that the problem might be the brake drum bearing I dismantled the stub axle assembly and replaced the bearing. Upon reassembly I found it made no difference. I have also tried putting an additional spacer between the stub axle and the brake plate assembly - no change. What I have noticed is that if I reduce the torque on the rear axle nut opposite (other side of the wheel from the stub axle) then the binding disappears. Can anyone give me a clue as to what is going on please? Any suggestions welcome.
Regards to all
bike drum brakes have to be…
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Thanks Robert
I did that as a matter of course. I then repeated to double check; sadly didn’t change anything.
Thank you for your reply.
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Hi Richard, I'm thinking…
Hi Richard, I'm thinking there is definately something wrong in there, Can you post a photo of the shoes ,or compare them to a known to be correct set. Also a picture of the brake cam , its possible to install it 180 degees out , It still works but with lost leverage. I'm not familiar with Commando's but it also sounds as if your speedo drive could be dished /buckled , does it rub the alloy cover plate?. A bit of open mind detective work for you !!. I would not be riding it till the issue sorted. I can't think of a worse job than having to be taking the rear wheel in and out.Consider putting those shoes ( Indian fakes?) to one side and buying some new from RGM ( gold woven linings) , If the old shoes turn out to be genuine get Villiers Services to reline for your spares box.
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It sounds...
... as though when you tighten the RHS end of the spindle it's pulling everything across causing the binding. I would suggest a missing / wrong spacer. You do have the central tube spacer between the bearings fitted don't you? This would cause a similar problem if not in place.
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Thank you both….
After reading your comments I dismantled the rear again. 
The attached photos show the shoes and cam which look ok to me.
Following your suggestion Ian I looked at the wheel to check the spacer was in place - it was. I then spent a rainy afternoon in my shed swapping parts in from my other Commando. Swapping out the wheel, spindle and speedo drive made no difference. However, swapping the brake drum/stub axle assembly did.
When recommissioning the bike I did notice significant score marks on the inside of the drum. Since there were no witness marks on the brakes shoes themselves I assumed that the PO hadn’t fitted enough shims between the stub axle and the brake plate at some point in the past.
I’m now thinking that either the drum itself or the stub axle is the problem…
Thank you again.
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What shims?
Hi Richard. In your last post you said that the PO hadn't fitted enough shims between the stub axle and the brake plate. I didnt know it was supposed to be shimmed out here. I changed my sprocket/drum recently. The old one was scored like yours but 10 times worse and when I reassembled the new one the bolt heads which hold the shoes on still caught on the rivets on the inside of the drum so I filled the heads down very slightly. Should I have put shims somewhere instead? I've never seen shims on any schematics. Have a look at the picture attached...what a mess!
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Not being a Commando owner …
Not being a Commando owner ,I don't know about shims. Its possible that the drum is dimensionally incorrect, there has been some poor pattern stuff. I know some of the linings on pattern shoes are completely useless despite "classic" branding, stick to RGM or similar. I have had to file off the edges of shoes/linings for clearance to the back of drum. Chain alignment could be an issue too looking at wear pattern. Looks possible for shoes to be bearing on ledge worn in back of drum.
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Hi Graham,
At the risk of the blind leading the blind, to quote Norman White “Check when the brake plate is installed into the drum that the two 1/4” screws clear the rear of the drum when rotated. If there is any contact then assemble one or more shims ( part no. 06 7603) to the dummy axle.”
The gouging in your drum, similar to mine, is caused by the heads of the two screws/bolts, that secure the “fixed” end of the brake shoes, making contact with the drum. Putting one or more shims between the axle and brake plate increases the clearance to avoid the problem. You don’t want to use more than necessary though otherwise you open the gap between the rim of the brake plate and the drum making contamination of the brake shoes more likely.
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Good point
I don’t know the history of the brake shoes so they may or may not be any good. I am travelling the next few days but when I get back I plan to try fitting the brake plate assembly from my known good machine in combination with the Mk2a drum and see if the binding problem returns. I guess I will then have my answer as to whether it is the drum or not. Richard, I take your point about the wear so I will replace the drum/sprocket anyway but I would like to confirm the drum is the issue first.
Thank you again everyone for your comments and suggestions. Always appreciated and one of the great benefits of our club.
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Thanks too
Sorry for nearly hijacking this thread but thanks Richard P for that much needed info and part numbers. Its always bugged me that something isn't as it should be, so it's great to know that this is how it is sometimes, especially as it's brakes, and that there's a fix. Cheers!
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bike drum brakes have to be centralised and some play in the assembly is incorporated to allow this . It’s usual to slacken the axle nut on the brake side, apply the brake hard and tighten up while holding the brake on .