Rear Brake drum

Information relating to the Matchless G12 or AJS Model 31 650cc twin
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Re: Rear Brake drum

Postby John Jarrett » Sun Jun 30, 2019 4:49 am

You never know what the cause might be.... I once had the same effect from a brake shoe that had broken in half.

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Re: Rear Brake drum

Postby Rob Harknett » Sun Jun 30, 2019 8:29 am

I had a mate with a Tiger Cub get the same effect, I found it was the brake anchor jumping. It was so worn, it was surprising the anchor stud did not jump out the slot it fitted into.

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Re: Rear Brake drum

Postby bob121 » Sun Jun 30, 2019 6:24 pm

Rob Harknett wrote:Just a thought, have you applied the brake and pushed it back and forth to try and see any movement of something that should not move, like brake anchor fitting. The movement you refer to seems to indicate some more at fault than the drum being a bit oval.


I have, with nothing obvious happening. My first thought was the anchor, as I was convinced that I had heard some knocking at some point. But on the ramp by hand no signs of anything untoward. I'll have to get the back wheel out and go over it.

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Re: Rear Brake drum

Postby MikeM. » Sun Jun 30, 2019 10:03 pm

my Greeves rear brake is oval due to a wheel rebuild, it was like it when I bought the bike nearly 14 years ago and I have adapted my riding to it, very handy on slow riding control as it can gently slow you down or in an emergency lock the wheel if too ham footed.

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Re: Rear Brake drum

Postby bob121 » Thu Jul 04, 2019 5:59 pm

Well, got a clearer idea of what is happening. I removed the rear wheel and drum the other day. Found some play between the plate and lug on the swing arm. But marginal. Shoes looked ok. Gave them a quick clean up. Checked the adjustment on the wheel bearings and found that the adjuster needed a turn and half. Put it all back together and the ride home was uneventful highlighting just the slightest amount pulsing in the pedal. However, after 124 mile ride today the wear in the stop is a major issue. So that will have to be sorted. And the speedo, as it's needle is stuck at 55 and the odometer and trip have stopped. And the oil leak at the dynamo. So the 2k service that's due is going to be quite extensive. But I did enjoy the ride today.

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Re: Rear Brake drum

Postby clive » Thu Jul 04, 2019 7:30 pm

The speedo stuck at 55 AND the odometer and trip have stopped working suggests that it is either the cable or rearwheel speedo drivebox that are at fault not the speedo. As soon as the drive enters the bottom of the speedo it is split into 2 distinct drive trains. one works the odometer and trip, one works the speed. Exceptionally unlikely they have both failed at the same time. I would start by checking the cable has not broken then check the drive at the gearbox is rotating when the rear wheel is turned. Any chance the cable did not slot back into the drive properly when you replaced the wheel?
clive
if it ain't broke don't fix

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Re: Rear Brake drum

Postby bob121 » Fri Jul 05, 2019 6:15 am

Cable seemed to drop in ok. Didn't need any persuading. Speedo worked for over 100 miles. How would the cable cause the needle to stick in one position? Doesn't it suggest that the issue may be the drive into the clock. I have seen that on an Enfield before. However, that was caused by the cable! It was putting pressure on the drive into the clock and it ground itself down slightly. Anyway, it's all guess work until I get a chance to look at it. I'll start pulling it down next week.

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Re: Rear Brake drum

Postby Winkie » Fri Jul 05, 2019 7:29 am

I am not a technical expert so cannot explain the mechanics behind it, but with a chronometric speedo the needle will stop at the speed it is showing when the cable breaks. Someone more knowledgeable than me will come along and explain why, but that is what chronometric speedometer do.

Old hat, I know, but check the drive on the back wheel carefully. You mentioned having to tighten the rear bearings. Loose adjustment can be an early sign of the speedo drive starting to seize - and that is no fun! Lots of earlier threads available about this issue.

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Re: Rear Brake drum

Postby bob121 » Fri Jul 05, 2019 11:02 am

Ta. Will investigate. Didn't know the needle would stop like that. Too many years with modern instruments. Hopefully it's just the cable. It's one of the few parts I hadn't renewed.

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Re: Rear Brake drum

Postby bob121 » Fri Jul 05, 2019 4:00 pm

Yep. Pulled out of the drive and worn a nice groove into the hub plate. And according to Google maps (on the phone I had on me) I did around 160 miles. That was without stopping. So overall I'm pleased with that. The issues however frustrating are minor and more than acceptable for the load I've put it under over the last nearly 2k miles.

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