Brakes

john998

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VOC Member
Have just made up the Bert Weitz mod on an already cut up brake plate and even with only one side modified it is a definite improvement. When you put the plate in with the two nuts slack and apply the brake it is surprising how far out the new pivots are compared to the old riveted ones, this applies to both the used shoes and a new set.
Now the question, with the new pivots only being clamped in the plate, especially if left slightly slack to allow the self centering, all the braking load from the shoes has to be taken by the cam.
Is this a safe situation? I am loath to cut up good brake plates if it proves not to be a good idea.
Thoughts please, has anyone been using this mod for a good period? John.
PS, I am that tight Yorkshire man Stuart.
 

stumpy lord

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Non-VOC Member
Have just made up the Bert Weitz mod on an already cut up brake plate and even with only one side modified it is a definite improvement. When you put the plate in with the two nuts slack and apply the brake it is surprising how far out the new pivots are compared to the old riveted ones, this applies to both the used shoes and a new set.
Now the question, with the new pivots only being clamped in the plate, especially if left slightly slack to allow the self centering, all the braking load from the shoes has to be taken by the cam.
Is this a safe situation? I am loath to cut up good brake plates if it proves not to be a good idea.
Thoughts please, has anyone been using this mod for a good period? John.
PS, I am that tight Yorkshire man Stuart.
Hi John,
clever trevor has a cut away brake plate mounted on a brake drum axle assembly so that you can see what is going on when the brake is applied, when the brake is applied, the first part of the brake shoe that contacts the brake drum is the trailing end of the shoe, every thing after that is the shoe bending. no wonder guys complain about spongy feeling brakes.
regards norm
 

john998

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VOC Member
Hello Bruce, thanks for that, what concerns me is the strength of the cam it's self.
Logically all the braking load is taken by the single peg on to the forks so the cam should be up to it.
But potentially removing the two pivots worries me. John.
 

davidd

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John,

I think it is a good question as to whether the mod is safe. I had thought about doing it to my rear brake on the racer. I decided not to do it. I think I decided that although the floating action on the leading shoe would help the braking, that the floating action on the trailing shoe would work against it. That does not mean the mod doesn't work, it meant to me that arcing the shoes properly and tightening up the hollow axle with the brake applied would probably create the same amount of benefit. I would guess that your braking is better with the modified plate because the shoes are not carefully matched to the drum and arced, otherwise, the loose pins would not move very much.

For those not familiar with the mod:
Burt Weisz Floating Pins.JPG


It seems to me that the mod is strong, but when it is tightened up it is the O-rings that are providing the floating action, which I would think is quite small even if beneficial. It is interesting that you see a lot of movement when easing the tightness of the fasteners, if I am following you correctly.

Trevor's display mentioned by Stumpy causes a lot of thought. It sounds like it matters less if your brakes are centered if the shoes are not capable of maintaining their original shape. It seems like the shoes are bending into the shape, but maybe they are also bending away from some necessary shapes also. There appears to be a lot of flex in all the components of the system, drum, shoes, pins, plates, balance beam, bridge plate and cable, to name a few. I fear that focusing on one or two soft spots may not help as the other soft spots will absorb and dissipate the improvement.

David
 

greg brillus

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It looks like a good idea, but then it becomes non-standard which people are reluctant to carry out. There are of course many brake assemblies on standard old British bikes that use floating shoes.......Look at the 8 inch twin leader that BSA and Triumph used on their late 60's bikes, and these brakes work very well when the linings have good contact with the drum surface. I have relined a few of these and unfortunately you cannot machine these down in the lathe, because if the lathe tool digs in and shifts the shoe (which can readily move) it would smash itself to bits. I pretty much machine all the brakes I do by mounting the brake plate on the lathe and machine down the oversize linings, and this works very well. You can see by the shape of the machined lining afterward how far out some of them are with relation to how they are positioned on the brake plate. I can see that if you simply installed a set of shoes with new linings bonded or riveted on and radius ground to size ( 7 inch) that this would yield poor braking performance, not unlike having piston rings of the wrong diameter trying to seal on a bore of a different size. I have found after setting up a set of brakes on a Vincent in the way I described, that the brakes generally work quite well, and having a good rear brake makes a huge difference to the all up stopping power. I know some who do not use the rear brake out of habit from riding modern bikes, but this is very important with old bikes with drum brakes ..........:)
 

john998

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Hello and thank for the replies. I have a cut away brake plate, so can see the shoes contact area.
The O rings have been left out as I fully tighten the 3/8 nuts after aligning the shoes in the hub, as I am concerned about the load on the cam. With the nuts slack the contract looks to be good, if you could leave the pivots floating from what I read you would have a servo effect but I am not brave enough for that. In the past I have tried centralising the plate before tightening the axel nut , but find it makes little difference, perhaps because the errors are so large.
Ideally the linings should be machined to fit the drum, but this only last until the leading shoe wears more quickly than the trailing shoe. With the adjustable, or floating pivot you can re position to allow for this, but come back to all the load on the cam. John
 

vibrac

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VOC Member
But...
Isnt this all negated by the new brake shoes* that reflect the 'error' discovered by Trev and produced by Goddet? or indeed a simple repositioning of the fixed pivot holes?
upload_2017-6-14_15-30-2.png

NB I have no connection with manufacturers. and certainly I cant afford to buy them!
 

davidd

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VOC Member
The new shoes certainly must help the stock brakes considerably. The question I would pose would be that if you list all of the parts in the stock brake system that are inadequately stiff or high friction you would get a long list. If it is a list of twenty items, for example, where do brake shoes come on that list? If the new, improved shoes are high up or at the top of the list, they may not be as expensive as you thought. Unfortunately, there is little information on the Vincent brake system that would allow this type of analysis, so we just guess and try out different things.

I think it was Neville Higgins that noted that all these mods seem to work for the first 50 miles and then the linings equalize and you are left with the same crappy brakes (that is a very loose paraphrasing). I would guess that linings, shoes and cables would be the first three on the triage list for stock brakes, but I am not certain.

Fortunately, Vincent Speet has done a great service to owners who are not tied to stock by building good brakes that cure many of the problems on the list. I am also glad that the 8" brakes are available for those of us who need to have a 2LS brake. These solutions are expensive, but seem to offer genuine improvements.

As a rule, I do not use the rear brake. This is mostly because the rear brakes have never seemed to work well for me and I was taught to use the front brake. I think Greg is correct that the rear brakes should be used as a habit. I wanted to stick with stock brakes on the rear of the racer for simplicity reasons and I saw it as a bit of a challenge to get it working well. I noted that rear bake shoes are activated in the opposite direction as the fronts, which favors the trailing shoe instead of the leading shoe. I will install a cast aluminum plate, reverse the brake arm, use good linings and a compressionless cable. I hope it proves reliable!

David
 

Vincent Brake

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VOC Member
For the ones who would need a "standard look brake" I can make my shoes working in a (inside heaviley modified ) standard steel brake plate and wider (30mm) finned drum. Alltough only one leading shoe.;)
You do the balance beam stiffening trick than.

let me know if there is any intrest

Vincent (Brake) Speet
 
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