brake anchor plate dimensions needed

Black Flash

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Hello and happy new year to all of you, even if I am a bit late now.
I have two sets of good looking but poorly machined front and rear alloy brake anchor plates. the central hole where the T-bar goes through isn't perpendicular in any of the plates for instance.
They came as parts with a basket case Rapide I bought 5 years ago and I would prefer to use them over the standard steel ones. They were sold to the previous owner more than 30 years ago by Ted Davies as I can see by the box they were sent in.
the easiest way would be to do some reverse engineering and measure the existing steelplates, but I remember that the positions of the pins in the plates vary and are not necessarily in the right place anyway.
In my quite rusty brain I can remember that there was a drawing -quite likely by clever Trevor- years ago which showed the positions in an ideal world.
If anybody can give me a hint where to find the drawing or even better post the drawing here I would be great.
I will owe you a beer should we meet any time anywhere.

Cheers
Bernd
 

vibrac

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In my equally rusty brain I have a feeling I read (and it was possible related here as well) that the original brake pivots had always been in the 'wrong place' for optimal brake efficiency,:confused:
 

Bill Thomas

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I think the way out of this is to make the centre hole bigger, When you put the wheel in, Hold the brake lever on before you do up the Spindle, Ron and me had to do this on steel brake plates, The other day, And he had to make a special thin spanner up , But yours do not have nuts. I had the same problem with Slater alloy plates many years ago. Cheers Bill.
 

Simon Dinsdale

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I think the way out of this is to make the centre hole bigger, When you put the wheel in, Hold the brake lever on before you do up the Spindle, Ron and me had to do this on steel brake plates, The other day, And he had to make a special thin spanner up , But yours do not have nuts. I had the same problem with Slater alloy plates many years ago. Cheers Bill.

Sorry this doesn't answer Bernd question, but....

If you open up the centre hole to allow the brake plate to float and find its natural position before tightning everything up, you may still not get the brakeplate in the optimum position. The brake plate anchor pin (this is the external pin not the pins the shoes go no) locates positively in the fork leg slot when the brake is applied it is this pin that transfers the brake force into the forks and thus the bike. So this makes the pin in a fixed position and so when you have an oversize central hole it can only move through an arc with the fixed anchor pin been the centre of that arc. With the wheel out the bike, try putting a loose brake plate in position with the anchor pin forced tight into its slot in the forks and them move the plate keeping the pin in the slot. It doesn't allow the brakeplate to fully float as really required when centralising.
So when the brake is applied, with the external anchor pin been a fixed position, the shoes touch the drum, centeralise through the arc previously described and if at that pint the shoe lining isnt in the perfect position, the shoes will bend slightly to achieve a better contact giving the feeling of sponginess at the lever. Sound familiar? Does that all sound reasonable, or am I talking nonsense?

In an ideal world you would centerlise the brake plate / shoes and then somehow lock a floating anchor pin where it is required. This is just theory as I have not tried it and as the anchor pin takes the braking load it would need to be very well secured otherwse could be dangerous.
As for the steel brake plates, I've yet to find an original that isn't warped in some way.

Simon
 

Simon Dinsdale

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Bernd

I made a set of twin leading shoe brakes last year for my Rapide using aluminium brakeplate castings. They are not my design, so I am not willing to put the drawings on the forum, but they were based on a very similar shoe to standard. The external brakeplate anchor locating pin is cast into the plate with a reinforcing web to strengthen it. I machined the central hole first, then using the central hole as a reference the o/d of the external anchor pin was machined to fit the forks perfectly. The plate anchor pin and the holes for the bolt on brake shoe pins were all machined on a 2-3/4" radius from the centre of the central hole, and this may be the dimension you are looking for.
This brake is a twin leading brake, but uses most of the geometry of the std Vincent brake. The result is an extreamly good brake that has no sponge feel at all. How it will operate later on when part worn I don't know, but the designer has been using his for 20+ years and they still work great.
 

chankly bore

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Sorry this doesn't answer Bernd question, but....

If you open up the centre hole to allow the brake plate to float and find its natural position before tightning everything up, you may still not get the brakeplate in the optimum position. The brake plate anchor pin (this is the external pin not the pins the shoes go no) locates positively in the fork leg slot when the brake is applied it is this pin that transfers the brake force into the forks and thus the bike. So this makes the pin in a fixed position and so when you have an oversize central hole it can only move through an arc with the fixed anchor pin been the centre of that arc. With the wheel out the bike, try putting a loose brake plate in position with the anchor pin forced tight into its slot in the forks and them move the plate keeping the pin in the slot. It doesn't allow the brakeplate to fully float as really required when centralising.
So when the brake is applied, with the external anchor pin been a fixed position, the shoes touch the drum, centeralise through the arc previously described and if at that pint the shoe lining isnt in the perfect position, the shoes will bend slightly to achieve a better contact giving the feeling of sponginess at the lever. Sound familiar? Does that all sound reasonable, or am I talking nonsense?

In an ideal world you would centerlise the brake plate / shoes and then somehow lock a floating anchor pin where it is required. This is just theory as I have not tried it and as the anchor pin takes the braking load it would need to be very well secured otherwse could be dangerous.
As for the steel brake plates, I've yet to find an original that isn't warped in some way.

Simon
Yes, I read somewhere that there is about a .040" error in the position of the brake cam drilling. Ted Davis's castings were rough and of questionable alloy , but in those days there was not much else around. I was always grateful for his advice and help. The local Section Spares has front and rear blank castings and front scoops in heat-treated 6160 alloy and I believe Terry Prince has also had them done. Personally, I would never trust an old steel plate; I don't think they were ever intended to do 60 years of service, ditto drums. Some Yankee guru said he just "straightened" the old steel plates- but that only betrays the infirmity rather than effecting a cure. An examination of the shoe pivot pins for parallel and dickandpurpularity is an instructive exercise, as is mounting a dial guage against the plate whilst applying the brake.
 

davidd

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It was Trevor that discovered an error on plates that he was working on.

Years ago I made a pattern for the rear brake plate and I ran across the tool I made to punch the hole locations into the plates. As Simon mentioned, they are all on the same diameter or circle. I would not know the number until I look at my drawing, but I assume Simon has quoted it correctly.

Ted Davis and Roger Slater used to make plates. Maughan makes plates also and it was a Maughn rear plate that I used as a guide for mine. I tried to order one and they were not available at the time.
Racer Brake Plate  1.jpg


I don't know how badly the holes are off, but I would think that you could bush the holes and resize the bush correctly. You can see the punch mark for the anchor hole that has yet to be drilled in the lower pad. All the other holes are on the same circle.

In terms of performance on the rear brake, I think the Series C rear brake arms all go the wrong way. I think the Series D brake arm is a better set up as it actuates the leading shoe with more lift much like the front does. The Series C actuates the trailing shoe on the rear with more lift. I am not sure that is a distinction with a difference once the shoes are worn in, but I prefer the leading shoe getting the lift like the design of the front brakes.

David
 

Bill Thomas

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Brother Ron, Did a job on a chaps Comet the other day, The shoes looked good and had been relined, To me they did not look 1950, But that is only what I think, The handle bar lever was a Joke !!, We took it apart and found one side was touching for a small bit nearest the cam, On both shoes, There was also a bit of run out in the drum, We thought we were stuffed !!, But Ron got out the biggest File I have ever seen !! and we opened out the hole a bit to one side and put it together as my other post above, We are now happy to bed the brakes in on the road. The slater plates were later known that the centre hole was not in the middle !. Cheers bill.
 

Black Flash

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A big thank you to all of you, for the quick help.
My idea is to fit oversize bushes and then machine the bores correctly. Regarding the brakearm orientation and leading /trailing shoe wear I am a bit puzzled with the standard Vincent layout.
When replacing the shoes on my wife's Citroen 2CV I could see again for the first time in many years that the brake lining on the trailing shoe was about 1/3 shorter in length than on the leading one.
I seem to remember that this was quite common with old Peugeot cars as well. the effect is quite clear, the contact area of the lining moves further away from the cam and due to this there is more leverage and higher pressuren/inch^2 on the trailing edge and as a result more wear.
this should in theory help to increase the braking of the leading shoe. it should work in theory and was also done. why did the works not do it?
or am I on a wrong path again?
Bernd
 
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