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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Seven Inch is in the Regulations
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<blockquote data-quote="davidd" data-source="post: 110523" data-attributes="member: 1177"><p>Greg,</p><p></p><p>Based on the description, I thought the Seeley shoe was a duo servo brake. It turns out that when I finally saw the inside of the shoe it was much more of a standard leading/trailing shoe. What Seeley did was add a floating cam as opposed to a floating pivot. It turns out that this is a fairly tricky thing to do. The cam pivot needs to be tight enough not to be pushed about, but loose enough to move as the leading shoe wears more than the trailing shoe. In the normal leading/trailing shoe you get a situation where the leading shoe wears faster than the trailing shoe and the leading shoe begins to be held from touching the drum with full force until the trailing shoe wears down a bit. This is called "equal work condition" but should be called "unequal work condition because you get this back and forth unequal wear as the shoes exchange decent wear rates. </p><p></p><p>I suspect many have noticed this. When you finish doing a brake job the brakes stop really well and your are patting yourself on the back. In a short while the leading shoe has worn a bit and the trailing shoe has not. The braking gets a little tepid. Now you are stuck in this cycle of one shoe wearing and then the other. Bill Hancock suggested using a soft lining on the trailing shoe. The lining would wear quickly and keep this uneven wearing cycle duration at a minimum. Seeley floated the cam in an attempt to do the same thing. It occurs to me that the floating cam could keep the leading shoe close to the drum, but it would not wear down the trailing shoe any quicker. So, you would have to swap shoes on the drum, front and rear to keep them equal, but I do not have any experience with the Seeley. I would note that Cam Donald liked the new Godet Flash, but I remember him saying the brakes were not good.</p><p></p><p>Duo servo brakes are used by the thousands, mostly in trucks as Bernd mentioned. I think that is due mostly to small cars having been converted to front and rear discs. </p><p></p><p>I still would not worry about spragging. I would start with a relatively low friction lining. Figure out where the front and trailing edge of the lining should be cut for the best braking and then increase the friction of the lining. As long as the brake is stable (not grabby) you're good. It is difficult to get too much servo action in Vincent brakes. You can't use the highest friction linings as they require too much heat to work. Very high friction linings require several thousand degrees of heat to wake up and stick. This is why many modern brakes are made from carbon. On a smaller scale, we would see this as the AM4 problem. The friction is great, but only if you are able to generate enough heat.</p><p></p><p>David</p></blockquote><p></p>
[QUOTE="davidd, post: 110523, member: 1177"] Greg, Based on the description, I thought the Seeley shoe was a duo servo brake. It turns out that when I finally saw the inside of the shoe it was much more of a standard leading/trailing shoe. What Seeley did was add a floating cam as opposed to a floating pivot. It turns out that this is a fairly tricky thing to do. The cam pivot needs to be tight enough not to be pushed about, but loose enough to move as the leading shoe wears more than the trailing shoe. In the normal leading/trailing shoe you get a situation where the leading shoe wears faster than the trailing shoe and the leading shoe begins to be held from touching the drum with full force until the trailing shoe wears down a bit. This is called "equal work condition" but should be called "unequal work condition because you get this back and forth unequal wear as the shoes exchange decent wear rates. I suspect many have noticed this. When you finish doing a brake job the brakes stop really well and your are patting yourself on the back. In a short while the leading shoe has worn a bit and the trailing shoe has not. The braking gets a little tepid. Now you are stuck in this cycle of one shoe wearing and then the other. Bill Hancock suggested using a soft lining on the trailing shoe. The lining would wear quickly and keep this uneven wearing cycle duration at a minimum. Seeley floated the cam in an attempt to do the same thing. It occurs to me that the floating cam could keep the leading shoe close to the drum, but it would not wear down the trailing shoe any quicker. So, you would have to swap shoes on the drum, front and rear to keep them equal, but I do not have any experience with the Seeley. I would note that Cam Donald liked the new Godet Flash, but I remember him saying the brakes were not good. Duo servo brakes are used by the thousands, mostly in trucks as Bernd mentioned. I think that is due mostly to small cars having been converted to front and rear discs. I still would not worry about spragging. I would start with a relatively low friction lining. Figure out where the front and trailing edge of the lining should be cut for the best braking and then increase the friction of the lining. As long as the brake is stable (not grabby) you're good. It is difficult to get too much servo action in Vincent brakes. You can't use the highest friction linings as they require too much heat to work. Very high friction linings require several thousand degrees of heat to wake up and stick. This is why many modern brakes are made from carbon. On a smaller scale, we would see this as the AM4 problem. The friction is great, but only if you are able to generate enough heat. David [/QUOTE]
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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Seven Inch is in the Regulations
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