I had the rear brake shoes relined and found that the rears brake was all but ineffective. I have had the wheel off several times and chalked the shoes to find high spots and filed these down. After several attempts at this the shoes still did not make a good comntact with the drum. So I gave up in the hope that with use they would bed in. 4000 miles and they are still useless.
I am used to centering shoes when installing them on other BSAs but could not see how you do this on the WM20 as the pivot is fixed.
Any advice would be very welcome.
From memory the hole for the brake pivot has some 'slop' in it. So I think you're supposed to slacken the nut then hold the brake on hard before tightening it up again. But in your case I think there might be other issues. Maybe you need softer lining from a specialist like
https://saftek.co.uk/ who understand about friction material for vintage vehicles.
Because I buggered up my right elbow many years ago, and am lacking in grip, I ride all my bikes by mainly using the rear brake. If I had your rear brake I would undoubtedly have been in trouble by now :cry: Ron
email (option): ronpier@talk21.com
Thanks Ron, I'll have an other go at finding some slack in the pivot. If that doesn't help I'll contact saftek.
I relined my M20's brake linings a few years ago, NOS linings purchased on ebay. To adjust the rear brake I tighten the adjustment wing nut until the wheel locks up, then back it off a bit. Works OK. Realize that the braking efficiency of a 75+ year old moto does not do justice to modern riding speeds.
Good luck.
Dave W.
email (option): Dwdiak4@gmail.com
Dean,
As Ron says your problem will be incorrect brake linings. I deal with Saftec all the time for my friction material (friction discs and brake linings). If you do it properly then they will need to know your drum material to match the the linings. They do a soft material that if you get oversize then you can then turn the linings on the back plate to match your drum size. Saftec offer this service if you take your wheel in to them. They also do a modern type of woven non asbestos material green in colour. I have been using this lately but it cannot be turned to drum size due to the woven make up so it needs to bed in. I find this woven material a better brake material than the soft linings they do but as i said you need to let them bed in. Once bedded in you will have a good brake for a girder forked bike.
email (option): t.j.walker@btinternat.com
Tim, thanks for the very useful information. This morning I tried the shoe adjustment Ron referred to but as I have a few running repairs to get through it will be a day or two before I can see if it has improved matters.
I am tempted to try softer linings although I had the front done at the same time with the same material and that, thankfully, is a good stopper.
I slackened off the pivot pin and applied the brakes while re-tightening it. Road test found no difference in braking performance, still virtually no braking effect.
I could try softer linings but I am not convinced that's the issue as the same material is in the front brakes and they are good stoppers, thankfully.
I'm at a loss as to where the problem lies. :-(
Are they rebonded shoes?....and are they the 'heavy' wartime shoes with a high zinc content in the castings?....These look like aluminium but weigh more than you would expect for that material....Ian
email (option): ian@wright52.plus.com
Hi Ian
I had them re-bonded. I don't recall them feeling particularly heavy. Are you suspecting they may be distorted?
Yes, the 'heavy' brake shoes are relatively unstable and distort during the bonding process. I've had similar effects in the past with regard to poor braking and that turned out to be the cause...
Remove the brake plate from the wheel and offer up the shoes individually to the drum to determine whether they are contacting correctly..Mine were a different radius altogether and had limited contact yet were fine before relining...Ian
email (option): ian@wright52.plus.com
Thanks Ian, that is very helpful information I'd have never guessed! I'll check the shoes.
If they are distorted I'll be needing a pair. The new ones I bought during restoration had to be sent back as they were too big so I found a used pair.
On my bike the fulcrum pin runs in a slot as Ron suggested. But after centering it won't stay put, moving around in the slot.
To secure the pin in place there's a serrated washer under the locknut, which I suppose is meant to bite into the metal of the backplate to keep things tight.I think the washer's seen better days & this might be the problem. Can someone advise, & are the washers available new?
Bob look for Nord Lock Washers.
https://www.ebay.co.uk/sch/i.html?_osacat=183900&_odkw=nord+lock+washers&_from=R40&_trksid=p2334524.m570.l1311.R1.TR2.TRC1.A0.H0.XNord+Lock+Washers.TRS0&_nkw=nord+lock+washers&_sacat=183900
However a sliding fulcrum post shouldn't make the braking any worse as it's then self centralizing each time you brake, much like the rear wheel cylinders on old Mini's used to be. They slid in a slot in the brake plate which would rust up and seize the cylinder and lose braking efficiency. Ron
email (option): ronpier@talk21.com
Ron
That was quick! Thanks.
Ta for the information about the washers. I'd had similar thoughts about the fulcrum pin centralising itself, the assembly as is seems to work OK. The manual I've got seems to imply the pin should be secured, but perhaps I'm worrying needlessly.
Quite right Bob. Fit a Nord Lock washer apply the brake hard and lock up the nut. Cheers Ron
email (option): ronpier@talk21.com