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Brake Plate Centering.

BigEd

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When I refit a wheel I usually hold the brakes on before tightening everything up to hopefully centralize the brakes in the drum. Reading the quote below from Tom Gaynor in another thread I have interpreted it that the Guzzi brake plate mentioned is free enough to move and centralize in use. Some Brit bikes had floating shoes that centralized in use and improved the braking. What if the Vincent brake plate had a clearance hole on the wheel spindle and suitable spacers to allow slight plate movement when the wheel was clamped in position? Comments welcome, rude or otherwise.:)

Something that came up at our lunch meeting today: contrary to popular opinion, the brake plates should NOT be a tight fit on the axle. If they can float radially, then the shoes will centre on the drum which is exactly what you want. If they are tight on the axle, then the drum has to wear the linings until they make maximum contact. As J Bickerstaffe once remarked, in that case the brakes are no sooner worn in than they start to wear out. I have a Guzzi 250, 8" brake, and it is clear that fit of the (steel) plate on the axles, and the nut on the outside, are designed to allow the plate to centre itself. It works. What is also important is that when the spindle is tightened there is a solid load path between the fork blades so that they don't close in. When I tried Lightning plates, in a vain effort to make what is effectively a 7" single leading shoe brake with a wide lining better, I had to put spacers in BEHIND the plates. Twin brakes do not double braking power, they double fade resistance...but my suspension still worked...
 

timetraveller

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The original steel plates were held on to the spindle by thin nuts and are not able to move radially but do flex. The much stiffer electron racing plates and the new machined from solid aluminium ones did, and should have, clearance holes in their centres to go over the hollow axle. This type of brake should have the brake lever firmly held on while the tommy bar central spindle is tightened. My experience is that the alloy plates, electron or aluminium, are much superior to the steel ones and if the little hollows at the end of each brake shoes are filled with weld and correctly profiled then it is possible to get about one and two thirds linings onto each shoe. With twin cables, rear brake arms on the front, the correct linings and in a panic it is possible to get the rear wheel into the air. Just don't ask me to do it again. Still no where near as good as disks though!
 

Alan J

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My front brake was pretty good till I changed the brake shoes- big mistake!! I have now done about 1000 miles and they are getting better! My back brake has always been next to useless-but fitting just one new "club spares brake" [thanks to Phil P.] has improved things no end! It seems 1 brake is better than 2 in this case!
 

clevtrev

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Some things to consider.
1 If you shim your brake plate to get minimum gap between drum and plate, remember the plate sits inside the drum, what do you think will happen if you try to move it over ?
With an alloy plate it sits outside the drum.

2 when a load is applied by the cam on to the shoe, why should the plate flex ? answer it can only flex if the pivot point is away from the cam, because if the load is at the cam, with the shoe touching the drum, how can the plate flex.

A fixed pivot brake can only operate satisfactorily once, once the shoe starts to wear, you`ve lost it. Provided that is, it was working once.
 

Bill Thomas

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Hello Eddy, Did you know the late, Roger Haylett ? .I thought he had some good tips. one of them was to elongate the holes in the shoes, Just a small bit, to centralize the shoes, It means you can't exchange them, but I shall give it a go next time I do the brakes, All The Best Bill.
 

BigEd

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Dear Bill,
I didn't know Roger Haylett personally but one of our Coventry section members has Roger's Comet. It has some interesting mods.

I found the front brakes on my Rapide to be quite good and put this down to the shoes still having "old" green lining material and play from wear allowing some (accidental) centralising to take place hence the interest in introducing some intended clearance to enable centralising.

Hello Eddy, Did you know the late, Roger Haylett ? .I thought he had some good tips. one of them was to elongate the holes in the shoes, Just a small bit, to centralize the shoes, It means you can't exchange them, but I shall give it a go next time I do the brakes, All The Best Bill.
 

Vincent Brake

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FLexing.

When having a closer look to the whole Org. set up, it flexes, thats for sure, Question is where? and how to overcome it?
The cam pivot bends inwards, as is the shoe pivot, both creating a force, thus flexing, on the steel plates, this is say 30% of the problem, as most worse is the flexing of the shoe itself, very near the pivot. When braking, the one shoe's leading edge takes about 70% of it all, this force is applying a bending moment on the shoes, remedy: weld it up at the back to near the pivot.
Next this force is in need of its counterforce (ok english??), to have 0 momentum on the plate, this comes from the trailing shoe, partly from this shoes leading surface near the pivot, this is by Phisical law limited to take this great force up. (allto be seen in braking motion) so here comes another problem of the to light constuction of the steel plates, as the big leading shoe's force has to be taken up mostly by the brake plate, through the pivot, It is very hard to overcome this problem, as there is an offset to the centre of brakeing (seen axially) to the point where the brake plate leads this force away.

I will post a pict. soon.

Besides, all I have done in my 2 x 2 LS brake set up, is to see to it that the stiffness of the shoes themselves take the most of the Normal (90 degrees) force creating the friction force, and there is of couse an equal counterpart taking on the created force.

Happy Braking.

Vincent (brake) Speet
 

stumpy lord

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Hi,
the back plates flex because on application of the brakes the first part of the shoe to contact the drum is the trailing edge of the shoe, after that it is the shoe bending that allows the rest of the shoe to contact the drum, the force required to bend the shoe causes the back plate to distort.
How do I know, well a few years ago clever Trevor arrived at a rally with his latest toy, one brake assembly set up as though on a bike, but this had the back plate cut away so that you could see it all working,and yes the first part of the shoe to contact the drum was the trailing edge.
Perhaps Trevor can be peruade to bring it to some of the vincent events and demanstrate it.
 

bmetcalf

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Bert Weisz had a mod with link plates on either side of the backing plate that held the pivot posts and allowed the shoes to float. I think it was in MPH, so maybe in 40YO or Whitakerpedia.
 

clevtrev

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Bert Weisz had a mod with link plates on either side of the backing plate that held the pivot posts and allowed the shoes to float. I think it was in MPH, so maybe in 40YO or Whitakerpedia.
They were connected together, so floated with each other, not individually. I have brake plates with individually floating shoes, and it did not make a difference, still poor. Interesting to watch the pivot points moving in opposite directions. `Twas only single leading shoe.
 
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