Author Topic: MOT Failure  (Read 2105 times)

Offline beezalex

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Re: MOT Failure
« Reply #15 on: 23.09. 2010 15:34 »
Radiusing the shoes to the drum should almost be a requirement.  Get some coarse sandpaper (60 or 80 grit) and either glue a strip of it in the drum or used double-stick tape.  Run each shoe around the drum until it is evenly sanded.  Be careful to keep even pressure on the shoe as you run it around so as not to tilt it.  Alternatively, it is sometimes possible to back the adjusters off enough to install the shoes with the paper in there.  I that case you can just rotate the wheel WRT the brake plate with gentle force applied to the brake until the shoes are evenly sanded. wink2
Alex

Too many BSA's


Offline Duncan R

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Re: MOT Failure
« Reply #16 on: 23.09. 2010 17:45 »
Thanks for the tip Alex I will give it a go
Anglo - Indian A7SS (Actually is a 650)
Kawasaki ZZR 1100
BMW R80GS
BMW R1100GS

Offline BSA_54A10

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Re: MOT Failure
« Reply #17 on: 24.09. 2010 01:30 »
Quote
Radiusing the shoes to the drum should almost be a requirement.  Get some coarse sandpaper (60 or 80 grit) and either glue a strip of it in the drum or used double-stick tape.  Run each shoe around the drum until it is evenly sanded.  Be careful to keep even pressure on the shoe as you run it around so as not to tilt it.  Alternatively, it is sometimes possible to back the adjusters off enough to install the shoes with the paper in there.  I that case you can just rotate the wheel WRT the brake plate with gentle force applied to the brake until the shoes are evenly sanded.

While this is better than nothing, it will actually put the wrong radius on your shoes unless you have fitted a hydraulic power assisted unit in there. They will be smaller than the drum by the thickness of the sandpaper & the tape.

 A non power assisted shoe should be radiused to a diameter slighter larger than the drum.
The theory goes like this.
The leading edge of the drum hits the drum and the rotation of the drum forces the shoe backwards into the pivot then flexes the shoe into full contact with the drum.
If the shoe is already a smaller radius then when the leading edge hits the drum the shoe can not flex enough to make a full contact which is why you see shoes that are only worn from 1/3 to 2/3 of their length.
If the pivot point is worn or too far away from the drum ( as would happen after skimming ) then the shoe ends up pushing the pivot pin backwards and looses contact with the drum.

Note this only applies to the leading shoe.
For peak efficency the trailing shoe should be as close to the diameter of the drum as possible.

If you are going to use the sandpaper in the drum method you need to move the pivot end of the shoe in till it contact the drum before you start to sand the shoe.
That is why professionals have those complex pivots which they use to radius the shoes.
If they were just to be round then it would be far easier to shove em in a lathe and turn them true.

My A65L with a comical front end and standard actuating levers will lock the front wheel at 70 mph with a three finger pull.
(It is a long story about how I found that out) .

If you really want to get into the mechanics of it there is a good series of articles on the victory libaries web pages with lots of numbers and charts and all sorts of stuff.

That is one of the own sides of the web.
The sandpaper method is good for cars and has been posted on a lot of vintage & veteran & classic car sites where it may or may not be appropriate ( depending upon weather they have power assistance or not) then it gets cross posted by some well meaning person who dose not have a full and proper understanding about how the brakes actually work. They might even go to their local brake works to verify the information where the brake fitter (who has never seen a fully mechanical brake) verifies that it should be Ok and after that it gets posted on every board in the world and become a "popular fact".

So that is the drum.
Put simply when the shoe is in position in the drum, the leading edge and the trailing edge should almost be touchine the brum and there should be more clearence at the middle of the shoe ( about 2 to 3 time the end clearence )
Bike Beesa
Trevor

Offline Duncan R

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Re: MOT Failure
« Reply #18 on: 24.09. 2010 09:20 »
Thanks for your postings on this.

I think I will leave as is for the moment - the brake is improving with more use, the MOT tester said it is a good working brake and the shoes will take a little more time to bed in. It does seem to have 2 bites,the initial application does not feel that strong but then progresses smoothly into a strong bite

Regards

Duncan
Anglo - Indian A7SS (Actually is a 650)
Kawasaki ZZR 1100
BMW R80GS
BMW R1100GS