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Re: Zinc alloy M20 brake shoes

The zinc alloy brake shoes aren't well suited to bonding..The heat required to bake on the lining is sufficient to get the shoe to a temperature where it becomes soft enough to distort...The effect of this is to alter the radius of the shoe...I had the problem myself a few years back...

Riveting on new shoes is really the answer for these in my experience...However, it would be worth a phone call to a relining specialist to discuss the problem as shoes of either type aren't that easy to find these days...Ian

email (option): ian@wright52.plus.com

Re: Zinc alloy M20 brake shoes

I don't live too far away from Saftek i will go over early next week and have a chat with them, I do know that the modern linings they bond on now is not suitable for riveting. They must have something suitable for these shoes. Any idea of the standard M20 lining thickness before i go over. I will report back once i have had a chat with them.
Tim W

Re: Zinc alloy M20 brake shoes

Tim the standards book gives .156" (5/32") and .140" acceptable at overhaul. Rivets are 5/32" x 1/2". Although I've never had to give anyone the sizes. Ron

email (option): ronpier@talk21.com

Re: Zinc alloy M20 brake shoes

Thanks for info Ron, reason i asked is a want to go oversize then turn to drum size. Saves me bedding the new linings in, will ask if they can rivet 3/16" linings.
Tim

Re: Zinc alloy M20 brake shoes

Making new brake shoes is on my list "to make" the fly in the ointment is the the steel insert. I must talk to my foundry man to see if he's happy to do it.

email (option): pes.sales@btconnect.com

Re: Zinc alloy M20 brake shoes

Just a word of caution - I was running an M.20 sidecar outfit a few year ago which had the brake linings bonded to zinc alloy shoes. Part of the rear wheel brake lining separated whilst I was on the road travelling at about 40mph and locked the rear wheel solid. If that had happened on a solo machine I would probably have come off in a big way but thanks to the sidecar everything remained upright although I left an impressive skid mark on the road surface.

I ended up dragging the machine to side of the road and removing the rear wheel and brake drum to discover what had happened. There was plenty of meat left on the lining that was still bonded to the brake shoe and the leading edge had been chamfered but a section including the leading edge had failed and broken away. This loose piece had been picked up by the remaining section of lining thus jamming the brake drum.

email (option): keithchandler@clistandchandler.co.uk

Re: Zinc alloy M20 brake shoes

I went a**e over t*t many moons ago when the same thing happened on a Bantam of all things.. Unfortunately, it was the front wheel that locked up and I was leaning on a roundabout at the time so there was no saving it... :laughing:...

Whether high zinc content shoes are more inclined to shed linings than any other I couldn't say but it is an interesting thought to ponder...Ian

email (option): ian@wright52.plus.com

Re: Zinc alloy M20 brake shoes

When I was an AA patrol one of the cars that had problems with bonded linings were the late model Ford Escorts. It usually happened when they were reversed the lining would detach and jam under the other shoe. Nine times out of ten this would happen in a multi-storey car park. Trying to get the drum off was a nightmare.

Re: Zinc alloy M20 brake shoes

Are later civilian brake shoes also zinc alloy or are they aluminum? My 1950 M21 will be due very soon for the shoes being relined.

Re: Zinc alloy M20 brake shoes

Later shoes are aluminium though you never know what has been fitted over time...The increase in zinc content was probably part of the wartime drive to save aluminium...

You'll know if you have the Zinc alloy shoes, they look like aluminium but weigh twice what you would expect..All of this only applies to the front and rear brakes on 'M' girder fork models or the rear brake only of 'M' models with tele forks and a rigid frame....Ian

email (option): ian@wright52.plus.com

Re: Zinc alloy M20 brake shoes

I went over to Saftek in Cleckheaton Yesterday and had a good chat with a very knowledgeable guy who has worked there for years. I took my M20 zink alloy shoes over for a chat about bonding or riviting the linings.
He knows all about the heavy zink alloy shoes and has relined hundreds of them using their bonding process. He assured me that the process they use to bond the modern material to these zink alloy shoes will not distort the shoe. He says that if they were distored then they have been over cooked or clamped wrongly in the process. I talked about different brake material and have chosen the woven type of material to be bonded as this material seems to work better with steel drums. They can also fit over size material so you can turn the shoes on the backplate to your drum diameter after fitting a shim between the shoes and cam. This is what i have chosen and will be ready at the end of the week with some Norton shoes i took at the same time.

Tim W

Re: Zinc alloy M20 brake shoes

Good to learn that Saftek know what they are doing Tim. I had one pair off Martyn Bratby that I had to throw away and buy some riveted shoes off him and another pair with brand new bonded linings that came in a job lot of spares that I couldn't get into the drum, so threw them away also. Ron

email (option): ronpier@talk21.com

Re: Zinc alloy M20 brake shoes

Something worth mentioning about new linings is that they are not profiled after bonding. Be it rivets or glue. The lining thickness is chosen from brake lining data books. The company I use has some very old books.
If the linings are over size, a good modern machine shop can circular mill a new profile. Much better than spinning the brake plate in a lathe.

email (option): pes.sales@btconnect.com

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