H: Hubs, Wheels and Tyres Eight inch brake ?

[stu spalding]

I don’t buy the argument that the standard shoes are insufficiently rigid or that a hardened alloy will give greater rigidity.
Regarding hardness, correct me if I’m wrong, but the Young’s Modulus for all aluminium alloys is in the fairly narrow range of 68.9 to 73.8 GPa and for a given alloy is not altered by hardening. So up to the point where the materials Yield Point is exceeded, a components rigidity is largely independent of the type of aluminium alloy or it’s hardness. Unless the standard shoes are being permanently distorted in use, indicating their yield point has been exceeded, surely hardening is of no benefit?
The mismatch between the dimensions of the standard shoes and backplate will massively increase the stress on the shoe and consequently may permanently distort it. But the answer is to correct this mismatch, which is a major problem even if the shoe is so strengthened that it doesn’t distort.

Thanks for that Rob, this backs up my own ideas about the standard plates and pivot pins flexing which is why the Bert Weisz mod works so well. Cheers, Stu.

 

[Bill Thomas]

I don't trust Glue, I had old ones slip round on my Vin' years ago, It was like an hydraulic brake, You could pump it , But it was the lining moving round, Sometimes in the right place sometimes Not !
Also, I had them come off a brand new Nissan Car, The owner of the Garage said I was a nutter, It was his car !.
Cheers Bill.

 

[vibrac]

Here is the shoe I mentioned I have been told it also corrects the geometry anomaly but cannot confirm this. I don't think Vincent Spares will stock them you would have to contact Goddet directly

Courtesy VOCSC & "The Black Shadow"

 

[timetraveller]

Is there anyone out there who has the necessary skills and equipment to check that what ClevTrev wrote many years ago? If I remember correctly he found that the pivot point on the standard brake plates was one millimetre too near the centre. Please correct that figure if I am remembering incorrectly. There are enough people who have access to modern measuring machines, and hopefully the skills to use these, so that this figure can be checked and corrected if required. If we can come up with a consensus as to what the error is then I know people who have cast and machined brake shoes similar to the ones illustrated. If it was a simple matter of machining the pivot hole in a different position then I believe that I could organise that. However, I do not want to waste time on an incorrect modification. Over to you.

 

[hadronuk]

Is there anyone out there who has the necessary skills and equipment to check that what ClevTrev wrote many years ago? If I remember correctly he found that the pivot point on the standard brake plates was one millimetre too near the centre. Please correct that figure if I am remembering incorrectly. There are enough people who have access to modern measuring machines, and hopefully the skills to use these, so that this figure can be checked and corrected if required. If we can come up with a consensus as to what the error is then I know people who have cast and machined brake shoes similar to the ones illustrated. If it was a simple matter of machining the pivot hole in a different position then I believe that I could organise that. However, I do not want to waste time on an incorrect modification. Over to you.

Oh dear! I remembered it as the pivot points were too far apart. Which was the basis for my view that this was the root cause of any shoe bending. If you are right, the stress on the shoes would not be much increased. Collapse of stout party.

 

[hadronuk]

Perhaps a good measure of shoe/drum alignment would be to check worn out shoes for excessive wear at one end?

 

[davidd]

David,

You mentioned "replacement shoes" - are you referring to current VOC Spares stock, or something else?
And a prior post in this thread alluded to some other shoes becoming available, but no details were given.
And a thought about the balance beam - It seems to me that it would equalize ("balance") the force on both sides, i.e. correct for some maladjustment so both sides of the brakes operated at about the same time and with approximately equal force.
And have you found some new brake lining material, better than the "Green Gripper Woven" material you mentioned recently?

John,

I did not find the reference, but I was probably talking about the Club shoes provided by Godet as replacement shoes. The stock Vincent shoes I have examined are laughably inadequate. I went through about 15 shoes and all of them were bent or severely deformed (meaning they were not necessarily bent but the arc of the shoe had deformed inward.) The good news is that they are so soft you can put them in the vise and straighten them out if they are bent. The deformation is more difficult because you have to restore the original arc.

I am a little surprised that some feel the shoes are fine. I would have thought that Trevor's front brake demonstrator, where you can watch the shoe deform as you apply the brakes would have been persuasive. Additionally, having review all of the brake mod articles done in the last 60 years I can only note that none of the mods have significantly improved the brakes. In other words, if all those mods were applied to Trevor's demonstrator, the front shoes would most likely continue to flex under braking. Finally, the only component in the Vincent brake system that has not been modified has been the brake shoes.

From a more modern point of view, I would expect to see the brake shoes used for rear brakes on modern motorcycles to have copied the Vincent brake shoe design if it were truly on the cutting edge of motorcycle design. That is not the case. Modern brake shoes are high pressure die cast design with almost 100% more material. Thus, I think the interest in a more robust brake shoe is well deserved.

There are some shoes other than Godet shoes being designed, but they have not been produced yet. I was hoping to use some new shoes to test out some modern linings. There may be linings that offer superior stopping performance to the Green Gripper, but they may not be suitable for other reasons. As a result, I think it is safest to use what has been tested. By the numbers, Green Gripper is superior to AM4 and it seems to me that AM4 performance should be the minimum performance that I would want to see. There are modern lining that offer more than double the coefficient of friction of AM4, but they need some careful testing. Increasing the coefficient of friction is a non-linear function. Historically, this increase produces much more fade due to the high heat generated by the high friction. Non-linear increases can produce grabbing, squealing and lots of dust.

I have some new brake shoes that I have nearly finished machining. When they are done I will clad them with .61 coefficient of friction lining. The AM4 is .44 and Green Gripper is .53.

David

 

[hadronuk]

Hi David, where can I find Trevor's front brake demonstrator? Sounds illuminating.

 

[stumpy lord]

Hi David, where can I find Trevor's front brake demonstrator? Sounds illuminating.

try clever trevor

 

[davidd]

Someone who visited Trevor gave a description of the set-up. It had a portion of the brake plate removed so the shoes could be scrutinized. When the brake lever is squeezed the shoes can be seen to flex when hitting the drum.

Trevor has been insistent on this for a long time. Here is a post from 11 years ago:

And, on the Forum the user name is "Clevtrev."

David