H: Hubs, Wheels and Tyres Seven Inch is in the Regulations

vibrac

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Perusing the race regulations for BHR,CRMC and Landsdown it would seem that original size brakes are mandatory so however good the 8" brake offerings are, they are a no go, however at least one organisation (CRMC)allow twin leading shoe modification now I did read here about someone(Erich Kruse?) who had done such a modification and I expect there are some other documents somwhere on how it can be done if some kind sole could point me in the right direction....
I am quite interested in an internal linkage but perhaps that is too much to hope for
 

Old Bill

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Vibrac, are you referring to Aluminium Brakes in general chat? Internal mech for tls but eight inch drums? Look good but l think the price would be interesting!
 

roy the mechanic

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According to C R M C eligibility, any drum brake of any type may be fitted, provided it was used in period. So, basically take your pick.
 

davidd

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I think Erich's system is best for the 7" shoes, if that is what you are limited to. I did email Erich years ago, but my German is not good enough to converse about technical items. He did make drums and plates. Some of his plates have been twin leading shoe plates.
Eric Kruse Germany.JPG


Twin Leading 7 Inch Kruse.jpg

His plate looks much like the one Paul Packman used (MPH 553) for his twin leading shoe conversion. Erich has flipped his levers forward and used two instead of the three levers that Paul used.

I would tend towards using the exposed linkages to start with. Bernd's design of the hidden linkages is brilliant, but on a racer I would like to be able to adjust the linkage lever ratios to get the maximum amount of braking force with the existing hand controls. That is a challenge with the hidden linkages.

You really want to get away from the Vincent brake shoes and use a good shoe. I do not know what Erich is doing about shoes. I would email Erich.

David
 

hadronuk

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I freely confess to owning a 1958 Tiger 100 with a 8" SLS as standard.
In spite of having better rigidity than a Vincent brake it is still remarkably poor.
Triumph later greatly improved it by making the shoes fully floating, so I was searching for info on how to modify my early brake when I found this:
http://victorylibrary.com/brit/SLS-TLS-c.htm

The page includes this diagram of how to make a SLS brake have a high self-servo action:
190mm-TLS-mod.JPG


As I understand it, only 2 mods are required:

1) The fixed pivot point is completely removed from the backplate and a shim placed on one shoe so that braking forces in the leading shoe are fully transferred to the trailing shoe and both shoes are now fully floating.
2) One cam lobe is ground off so that the remaining lobe only acts on the leading shoe. The trailing edge of the trailing shoe now abuts a constant radius on the back of the cam.

A few thoughts.
I can see it might give powerful braking, but it sounds like careful adjustments to the linings will be required to avoid locking up due to excessive self servo action.
The cam now carries all of the braking forces.
Additional provision such as anchor springs may be required to keep the shoes from moving sideways.

Anybody tried this?
 

Bill Thomas

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Ron and me used 2 cams per side and fully floating, On alloy Slater Plates, Early 70s.
It was good, But not as good as I needed. Cheers Bill..
 

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davidd

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I contemplated making a dual or duo servo brake for the front, because it appears to be a leading/trailing shoe. However, upon rereading the rules they specifically required the bike to have a trailing shoe. I saw that as a stopper.

The duo servo shoe has a primary and an secondary shoe. Those shoes are both linked together (where the pivot would otherwise be). The leading shoe has a cam and the trailing shoe has a solid abutment to hit so it does not move. That abutment could be the constant radius cam or a lump welded to the backing plate.

The real trick is that when you move the cam both shoes are forced by one the single cam to move in the direction of the rotating wheel, which they will gladly do. As the leading shoe (primary shoe) grabs the drum, the drum it is jamming itself into the into the trailing shoe (secondary shoe.) Because the back end of the secondary shoe cannot move due to the constant radius cam or the abutment, all that force causes the secondary shoe to be pushed hard into the drum. Because the back end of the leading shoe is connected to the leading edge of the secondary shoe it is pushing hard on the leading edge of the secondary or trailing shoe. Exactly what you want!

brakes-drum-chapter10-45-728.jpg


Just for clarity, the blue colored abutment at the top would be attached to the backing plate or it would be a constant radius cam.

The cam, which is not shown, would be pushing the shoe where the small red "block" arrow shows. The cam is shown at the top of the drum here, but it could be rotated to the bottom.

At the bottom under the link is another "block" arrow showing the transfer of force from the primary shoe to the secondary shoe. The leading edge of the secondary shoe is the one that is being forced into the drum by the link.

The one sided constant radius cam from a Triumph is shown here:
Triumph Sliding TLS Cam.GIF

The cam lobe is on the bottom in the photo and the other lobe does not exist, but is a constant radius so the shoe that is resting on this side will not actuate even as the cam spindle turns. This way it works one shoe only.

I have read that these brakes are better than twin leading shoes in terms of braking. I have also read the the primary shoe does not generate as much force as the secondary shoe. This would lead me to believe that a twin leading shoe might have a bit of an edge. I don't think you will have to worry about spragging with this brake design any more than on twin or 4 leading shoe brakes, but it pays to be careful.

David
 
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greg brillus

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Hi there David, is that type of brake the same as Patrick used on the Isle of Mann racer that used a Sealy brake. It is one that we discussed some time ago......... All the 4 l/s brakes i have played with have either circular anchors and strong springs, or a pin with a matching diameter hole in the shoe and a circlip to hold in place. These include the Suzuki water bottle, replica Ceriani 230 mm, and replica Fontana 250 mm.
 

vibrac

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Dual servo all seems viable and would be leagle for racing but I don't like the phrase " excessive servo action" I certainly would want conclusive practical examples of its use
 

greg brillus

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I think the excess servo action is probably down to careful set up and adjustment as the brake linings wear. In most old cars from the 70's if the linings get worn the brakes get very snatchy, almost send you through the windscreen when you touch them. This on drum brakes of course, and with a vacuum booster to add the extra fluid pressure.
 
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