H: Hubs, Wheels and Tyres Eight inch brake ?

[BigEd]

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

Dear Rob,
In the Databases > Resources there is some information. It is from MPH 499, page 16. I have inserted a link below:
To Stop Or Not To Stop

 

[timetraveller]

OK. I was wrong and Hadronuk was right. Trevor's finding was that the pivots are too far out from the centre and not too far inwards. That could be compensated for by machining the pivot holes one mm further out from the cam end. What do people do when they machine the linings prior to fitting them into the drums? In my case I made up a fitting which will fit into a three jaw chuck on the lathe and machine from that centre. I think that should be an improvement but what do others think? The other thing which I always emphasise is that when using ali brake plates the hole in the centre should be at least 2 mm larger than the diameter of the hollow axle. This goes back to the original Vincent 'Work Sheets' where such a method was advocated by the works. Remember that with the ali plates there are no thin nuts. The idea is that the brakes are applied hard before the tommy bar axle is tightened and this allows the brake plate plus shoes to centre themselves in the drum. It works for me but whether the brakes are as good as they could be if the geometry was correct in the first place can only be determined by experiment.

 

[Bob]

Here's a mod I've done to my Rapide's brakes (apologies if it's been done before).
It allows centralising, and adjustment of the shoes. To do this slacken the nuts, adjust the shoes if necessary, apply brake and tighten.
The pics are self explanatory. I replaced the fixed pivot pins with ones I turned up. These have threaded extensions that allow plenty of movement in the original holes.
The small pin slides in holes in the new pivot pins thus preventing rotation when the nuts are tightened.
The brass adjuster has rh/lh threads.

 

[Peter Holmes]

Looks very good, and clever too, how does it perform?

 

[Bob]

Thanks Peter. There has been a huge improvement to what I had before and the shoes are making good contact all around.

 

[stu spalding]

Here's a mod I've done to my Rapide's brakes (apologies if it's been done before).
It allows centralising, and adjustment of the shoes. To do this slacken the nuts, adjust the shoes if necessary, apply brake and tighten.
The pics are self explanatory. I replaced the fixed pivot pins with ones I turned up. These have threaded extensions that allow plenty of movement in the original holes.
The small pin slides in holes in the new pivot pins thus preventing rotation when the nuts are tightened.
The brass adjuster has rh/lh threads.

Hi Bob, you almost got the Bert Weisz mod. Try a single 1/4" thick base to press the pivot pins into, drilled at 1" centres. This will accurately locate the shoes while allowing movement to self centre. Cheers, Stu.

 

[vibrac]

Nobody has ever said if the spacing anomoly was propergated onto the racing plates or any of the reiterations in alloy that started with Roger Slater (Theres a name to conjure with)

 

[bmetcalf]

Yes, I wonder if the Drawings Committee considered Trev's observation?

 

[davidd]

.I discussed this with my brake man and he now uses less pressure when clamping the linings to the shoes.................I can see how this could be a universal problem that may affect more than just one bike out there. It is also likely to happen because the shoes are very narrow and are quite weak in design. Any thoughts..................???

Greg,

I thought this might be a problem. I found that the bonding oven temps are around 475 F and I did a quick check of alloys and did not see an obvious problem. However, I don't know what the quality control is on the oven settings and it is obvious that the stock Vincent shoes become very damaged through use, so they may also be damaged during the bonding process.

I don't believe this would be a problem for the modern high pressure aluminum die cast brake shoes used on modern motorcycles, because they are all bonded. Generally, the modern shoes are a lot more rugged in design, also.

Ultimately, I think it is better to fit a more robust replacement shoe. I know the existing replacement shoes are too dear to garner much interest, but trying out a robust shoe with a high friction lining would be a good "proof of concept." I have some high friction linings on a set of stock shoes and I hope to put the same linings on a new shoe to get some feedback on the difference. Both are bonded.

David

 

[davidd]

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

Rob,

I think that determining the correct pivot points would be a difficult task. In fact, I think Trevor said as much earlier in the post. But, brakes with pivots always will display asymmetric wear. The leading shoe will also wear more compared to the trailing shoe, as has been discussed. I think the best way to solve the problem is to replace the pivots with floating ends. Floating shoes have a "virtual pivot" point and produce very even wear.

I think this can be done by simply cutting off half of the pivot ring on the shoe. I have not figured out the shape of the pivot that remains, but I suspect it could be milled in a slight "Y" shape. You would need a second spring near the floating pivots as a return spring. This mod would also allow you to join the two pivot posts with a plate so that they support each other and do not bend towards each other as they do on the steel backing plates.

I think floating shoes would be a pretty good substitute for pivoted shoes.

David