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FT: Frame (Twin) New 7" Brake Shoes


timetraveller

Well Known and Active Website User
VOC Member
There was a time when replacement brake shoes for the post war bikes were difficult to source. I have been involved with the development of replacement shoes and a photograph is shown of the items. They are made of LM25 heat treated and several changes (hopefully improvements) have been made to the originals. They are stiffer than the originals by incorporating stiffening webs. They do not have the small tongues sticking out to take the springs. Instead they have robust through holes. In addition they do not have the dips at the end of the brake linings which allows a longer lining to be use if wished. They will be supplied in pairs only, complete with the spring and metal end plates (H48) fitted. The price, per pair is £80 and you can organise the fitting of your preferred linings if you wish. Alternatively, they can be supplied with linings suitable for touring use or alternatively for racing use if you wish. The price for touring linings fitted is about £12 per shoe.
1584699618857.png
 

peter holmes

Well Known and Active Website User
VOC Member
Norman, These look fantastic, and great value, please put me down for a complete set for B-C, 4 x pairs, ready to be installed with touring linings, money up front if that is required. Cheers Peter
 

Albervin

Well Known and Active Website User
VOC Member
Norman, they seem to be great value. I have been using springs with toggles (if that is the correct description). The idea is that if there is any judder/shudder the toggles will reduce the chance of a broken spring. Also, I have more recently been sleeving the spring with rubber to again reduce the breakage of spring. This all came about when I first fitted some Lightning replica plates and had massive squeal. As you know, noise and heat plus old bikes leads to complications. After only a forty mile ride a spring broke and it is best said the ride home was not fun. Your thoughts.
 

timetraveller

Well Known and Active Website User
VOC Member
I am not sure that I have anything useful to say about squealing brakes and broken springs. The problem is an old one and decades ago people were putting a soft wire through the spring so that if it broke it could not fall into the braking mechanism and jam up the front wheel. You would still not have a proper brake but at least you might get home with care. Some of the Lightning replica brake plates were of very poor quality. Made in aluminium and with cast in air scoops they looked alright but were often poorly machined. The new replica Lightning brake plates, machined from billet, are much superior and although often maligned I was taking apart a genuine early Electron brake a couple of days ago and the electron still with stands a hammer blow with no problem. They have been kept dry.
The idea of filling in the hollows at the ends of the brake lining to allow a much longer lining is also not new. I have these on the ex-Cecil Mills bike and that modification dates from the early sixties at least. I am not enough of an expert on brakes to feel confident in arguing the case but it seems to me that more lining in touch with the drum should be a good thing. The new design allows a more than 50% increase in lining area if one wishes and that is what I have used on the ex-Cecil Mills bike for over 50 years. In a panic I did once have the rear wheel off the ground when a car pulled across in front of me but do not ask me to do it again.
If the question is 'will the new design stop squeal?' then the answer is that I do not know. I suspect that squeal has a lot to do with lining, drum and brake plate material and stiffness Certainly the new brake shoes are much stiffer than the originals. Perhaps we will get some feedback when some have been fitted and used in anger. I doubt that these springs will break and the method of attaching them to the brake shoes is much stronger than the original
 

oexing

Well Known and Active Website User
VOC Member
Breaking springs seem to be a real problem in the Vincent society ?? I have made lots of stainless steel springs on all sorts of places and never ever had broken springs. Stainless is a bit softer than normal high carbon steel but this is rarely a factor in most cases. So maybe it would be a good idea to switch to stainless, for kickstart too, seems to be a trauma there . Seems the standard kickstart spring is a bit overstressed with the range it has to cope with,my stainless type looks promising, road use will tell. For valve springs this is no option for sure, you need very specialised material there.

Vic
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Nigel Spaxman

Well Known and Active Website User
VOC Member
Vic
What is the little plate covering the end of the crankshaft for? I like the look of the buffers you made for the kickstarter quadrant. They look a lot nicer than the original system.
 

Vincent Brake

Well Known and Active Website User
VOC Member
Hi Norman,
Can you write me up for 8 sets please.

Not racing but normal linings.
And please as far as possible to the cam side.
Cheers

Vincent
 

oexing

Well Known and Active Website User
VOC Member
The part over the crank end is a barrier to get a higher oil level in the timing case. My idea is to have a lot more oil splashing around there for gear and cam lubrication and quiet operation. This is only inspiration by gut feeling, will take a year or two for proof. The old draining hole is blocked and a new one higher up is active. Well, lots of variations on these engines but still untested, still some time to go for my reconstructions - and some more mods in my mind.

Vic
 

davidd

Well Known and Active Website User
VOC Member
The idea of filling in the hollows at the ends of the brake lining to allow a much longer lining is also not new.
Norman,

Congratulations on providing another important product.

Phil Vincent was very careful to make sure that brake reliners could not screw up the complicated geometry of the lining placement. This is why he cast in the "dips" in the shoes. The dips forced the lining to form a 90 degree arc on the shoe. The angle is important, but having looked at the math many times I don't think there is a more complicated item on the bike than the brakes.

Because I do not understand the math I can only conclude that the 90 degree arc is a conservative choice for touring bike and is not necessarily chosen for maximum performance. I think this is fine. I use Japanese brakes and they have flat lining beds, so I have the same issue.

If you wish to have original Vincent style lining geometry it is fairly easy. Just tell the brake reliner to cut a 5.25" piece of lining and center it on the shoe. If you measure your linings and they are longer than you wish, just grind the lining back (there is no asbestos, but do it safely).

The standard for brake reliners is to line the entire lining bed and they expect the customer to "tune" the lining to suit by grinding. Most folks have no idea how to tune their linings, but racers usually do based on lots of trial and error.

The extra lining area does nothing. It may impair the brake performance. The Ferodo lads say this is so for a number of reasons. First, the lining needs to be mounted where the geometry works best to get the highest amount of servo action, not to get the most lining area. Second, the lining at the ends of the shoes is not able to grip the drum because there is no pressure at the extremes ends of the shoes. This can be seen clearly on the pivot ends which cannot move out toward the drum. Although the cam ends move, they don't move towards the drum. They move left and right. The center of pressure of the the shoe is near the center of the shoe. The forces look like this:
Lining Pressure.PNG
This is another reason it is difficult to get better performance by increasing the length of the lining. There just is not a lot of braking force happening there.

Third, and very important, the longer the lining the more clearance you have to adjust into the shoe. The Ferodo lads are very specific about this. The shorter the lining the less clearance you can run, so the shoe can be a hair of the drum. This generally works better for hand actuated brakes because of their limited travel.

I would offer the shoes with whatever lining your supplier deems useful. We know that the lining can be trimmed back a long way before getting to stock.

As for squeal, I use Triumph brake springs on the Japanese linings, just based on availability and fit. All your comments are right on point. One item that is not often thought of is that the lining itself wobbles around wildly when it is new and quite tall. This is why you need a long bevel to ease into the drum. The reason you never have to bevel a used lining is that as it wears it becomes much more stable. But, put a good bevel on when it is new.

One of the weak spots is the H48. The plate is too soft and maybe too thin. I made the decision to stick with the Japanese shoes for this reason only. The Japanese shoes have very thick hardened steel cast-in inserts.

DSCN1999 (37).jpg
The H48 is double thick on the one in the above photo, but I have found many like this:
Brake H48 .jpg
With this type of detent worn in the brakes cannot work well. The cam falls into the detent and no more brake force to the drums. It is worth changing these at the first signs of deforming.

David
 

timetraveller

Well Known and Active Website User
VOC Member
Thanks for all that David. New H48s will be fitted to each new shoe so should stand up to the pressure for quite some time. If it really turned out to be a problem then it would be possible to machine back the castings and provide a thicker H48 but they would not be easy to form from a thicker material. As you write. if longer linings are fitted then everyone who wishes can trim them back to where ever they want. My own use with the longer linings over about 50 years has never shown a problem but the bike is set up with twin brake cables and the longer rear brake arms are used on the front. The wear on the linings was even over their whole length but the Ferodo people certainly know more about this than I do.
 

Chris Launders

Well Known and Active Website User
VOC Member
Would there be an advantage using elliptical instead of flat cams ?
I'm sure some clever programmer could work out a shape and the force applied to the shoe.
 

vibrac

Well Known and Active Website User
VOC Member
As regards the H48 one of the few good design features of the AMC line is the pad at the shoe/cam interface
1584783173123.png
There is not a lot of meat in a vincent shoe end but I wonder if an option like this is possible/
 

Bill Thomas

Well Known and Active Website User
VOC Member
I would have thought the longer lining would get rid of heat better ?,
So you could use a very soft lining ?,
Or we would all be using linings about 1/2" long ?.
If I can find some money, I would give it a go.
 

Vincent Brake

Well Known and Active Website User
VOC Member
Hi David,

In your drawing;
The forces on the brake are true only, if you have a standing still brake drum.

Its a total different situation when you let that one roll
Than you see the Trailing/Leading effect.

Specially the leading one should have its lining as far possible to the cam side.
 

davidd

Well Known and Active Website User
VOC Member
Vincent,

I should have been more specific about the source of this material. This is not my work. It is the work of Newcomb & Spurr, who were the top engineers at Ferodo. It is in their book: Braking of Road Vehicles.

The pressure lines are a relatively accurate drawing of the pressure on a fully lined leading shoe in motion. If there were a corresponding trailing shoe in motion opposite the leading show it would look the same, but the force lines would be only about 1/3 the length of the leading shoes. The drawing is done to demonstrate the relative difference between the center of pressure and the areas of lower pressure on the same shoe. It does not show the difference in pressure between a leading and trailing shoe.

Brakes_simplex_SLS_explained.jpg
This is a good example of the difference between leading and trailing shoe forces. on the left is a pivoted system. I think it is a good example of showing that when you trim the lining back you do not lose a lot of force, but you certainly start to "square it off" in terms of the graph. Volvo did not like the wear in the leading shoe, based on their scheduled service intervals. By tuning the lining (cropping it back at the leading edge) they decreased the servo action of the leading shoe and made the wear on the shoes a bit better. This is also a rear brake and manufacturers tend to detune the rear brakes, on motorcycles particularly, to keep the rear braking at a minimum.

There is nothing wrong with wanting the lining as long as possible at the cam end even though the maximum force is closer to the pivot end. Instead, at the cam end, of a leading shoe you have some control of the servo effect. It is difficult to get too much servo effect, but when you do the front brake will be
dubbed "grabby". The compromise is usually in the lining material. It is difficult to make low friction lining grabby.

Would there be an advantage using elliptical instead of flat cams ?
I'm sure some clever programmer could work out a shape and the force applied to the shoe.
Chris,

The cam design of the Vincent is difficult to work with because it is flat. Because it is flat, it lifts each of the shoes to different heights and pressures. On the front, the lift favors the leading shoe. On the rear, the brake arm is turned so the lift favors the trailing shoe. This is part of the detuning the rear brake that I mentioned.

The shape of the cam can be changed to an equal lift and pressure using an "S" involute cam.
3-s2.0-B9780750651318500129-f11-14-9780750651318.gif

I do think you could fool around with the shape of the stock Vincent cam and get some beneficial effects. Many years ago an owner from Chicago named Wozney, if I remember correctly, came up with a design.

David
 

oexing

Well Known and Active Website User
VOC Member
Sorry for showing another BMW part, they have come up with a redesigned brake cam for their twin leading shoe brakes in the fifties and used this up to /5 series drums as well. No steel capped shoes used, no need for that. The motion is mainly lifting the shoes, only minimum rubbing effect. The shoes are same but cams are different because no rod link between cams with push/pull operation cable outer and inner. I am planning to do four leading link 200 mm brakes with these shoes. In the photo two new shoes laid over a used brake set.

Vic
P1050633.JPG
 

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