The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => Frame => Topic started by: a101960 on 15.01. 2020 11:04
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I have seen it mentioned several times that the 8" (and presumably the 7" too) brake can be improved by reversing the lever. I have also read that BSA did this on their track bikes. Obviously reversing the lever is simple enough, but how would the cable be anchored to the brake plate? Has anyone done this, and if so what was involved? I think there is probably a lot more to it than first meets the eye.
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Lots of info in this thread inc a pic of a reversed lever
https://www.a7a10.net/forum/index.php?topic=13886.15
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this is how I did mine , the big holes were air outlets and behind the brake lever arm are some small holes where a scoop was fitted before I had the bike 40 plus years ago. the big nut next to the arm is what fastened onto the brake plate and fork arm in the hole that is visible, that is the original fixing, you can see the small drain hole at about 9 o'clock and those big holes were at about 9 0clock. so I drilled the torque arm and left the original hole just in case I wanted to re fit the air scoop. so basically the brake plate is turned a bit, hope photo helps
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Has that mod made a big difference?
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greybeard it is so much better, when a goldie racer showed me how to do it I pushed his bike on his drive and pulled the brake on and it stopped dead, I pushed my bike the same and put brake on and it didn't stop dead, but after I did this it now stops dead on a push, so its a lot better on the road now. a good job really because the back is crap and while the bikes in the kitchen for gearbox swap it will be getting looked at AGAIN!!! *bash*
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What makes is work better? The cam attached to the arm still rotates the same amount for the shoes to make contact with the drum, right? Trying to think of anything, so, grasping at straws. Could it have to do with the cam-ward end of the shoes being rotated behind the fork bottom rather than in front of it, then, some magic of better contact as the front end dips down on braking.
(Don't ask me to make real physics logic out of that.)
Signed,
Clueless
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Richard the ins and outs of it tax my brain cell, *pull hair out* *dunno* but it works *conf2* and since doing it i have seen pictures of factory race bikes with the same set up
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What makes is work better? The cam attached to the arm still rotates the same amount for the shoes to make contact with the drum, right? Trying to think of anything, so, grasping at straws. Could it have to do with the cam-ward end of the shoes being rotated behind the fork bottom rather than in front of it, then, some magic of better contact as the front end dips down on braking.
(Don't ask me to make real physics logic out of that.)
Signed,
Clueless
The cam is basically a flat lever
The side that the inner edge works against moves faster & contacts the the drum first
The one where the cam works against the outer edge contacts the drum a tad latter but pushes harder.
If the cam ever gets to be at right angle to the shoes then these forces would become equal.
For the brake shoes to move at equal speeda and equal distances hen the contact face on one or both needs to be cut at a slope with respect to the position of the brake cam at rest.
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The original arrangement is pretty good - when a deer jumped into my path the squeal from the front tyre was louder than the one I made...
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BSA used this on the A10 full width hub rear brake when for the 1960 season they changed the brake operation by pointing the lever downwards rather than the previous season pointing upwards. The claim in the catalogue was "improved operation for greater efficiency".
Did it improve the cable rear brake?
The left side rod rear brake with the lever pointing down was already set up like this.
The same effect was achieved in some scooter brakes (Triumph and some Lambretta as far as I recall) by using an eccentric brake cam.
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I tend to think it's a psychological thing, like a disk brake on modern bikes, where the brake caliper is mounted before or behind the fork leg (rotation of wheel).
It would seem that a caliper mounted before the leg is more efficient as the "pushing" action from the disc makes the pads "clamp" together thus producing more braking force.
Logically this can't be true as wherever on the circumference of the disc the caliper is mounted, the efficiency of the brake would be the same.
Or am I talking complete bollocks here? *dunno*
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err yes morris but I talk loads of bollocks without being encouraged , BUT my experience of the brake when doing the push test on my bike compared to his convinced me to try it out. and when it was done without alteration to the shoes it DID work and the bike then stopped dead when giving it a good push whereas before it carried on forward a bit. I think I know why my back brake is not very good, I think I need bigger boots now I have lost a lot of leverage by making this brake pedal *eek*
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Revisiting the link mentioned above opened the can again and there were certainly lively points of view at the time. I think it was GB who nailed it with a simple illustration.
With a symmetrical cam, both lobes will start to move the shoes at the same time, but when you think about it the contact point between cam and shoe is not the same distance from the shoe pivot for each side of the cam.
One cam/shoe contact point is nearer the pivot and this shoe will touch the drum first. When this shoe is the leading shoe, that is when you get the best performance, leading and trailing shoes, servo action etc, it was all mentioned.
As an example,Plunger rear brakes are pretty good, wheel moves anti clockwise in forward travel brake lever move clockwise, leading shoe on top, cam/shoe contact point nearer the pivot compared with the lower trailing shoe. The opposite happens on the standard 8" front brake, the leading shoe cam/shoe contact point is further from the pivot than on the trailing shoe. Lever and wheel rotate in the same direction. Simply reversing the lever moves the cam/shoe contact point on the leading shoe closer to the pivot, (the lever and wheel rotations are opposed), as on the good rear brake, and by all accounts (inc bergs) much better brake performance results.
Swarfy.
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Right, see the point.
But I’m one of those kind that always have to see before believing... so Bergs, don’t be surprised if I show up some day ;) *smile*
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Hello forum, this is my first (after my introduction) post and I am a learner amont lots of experts here. I hope, it is OK to add some ideas to an olt thread but I assume, the arrangement of the rear and front brake levers are due to the fact, that at least the A10s were also intended for sidecar use. So, if the threewheeler setup is rolling backwards, you must have a brake that stops the vehicle. From that point of view the front brake is the better stopper in rearward movement. That is my theory, as I am not a sidecar owner. At my Zündapp K500 both brake levers rotate against the wheel and both brakes are quite good. The Zündapp KS600 has the rear brake lever rotating with the wheel. The KS600 was mainly designed for sidecar use - the K500 not.
In https://www.a7a10.net/forum/index.php?topic=14952.msg125587#msg125587 BSA_54A10 wrote in very short and clear words what former chief editor of the German magazine "Motorrad" Carl Hertweck wrote in his famous book "Besser machen" (make it better) in the early sixties. It is about all the little and bigger problems, the motorbiker hat to face with and how to help himself. The book is available in a reprint in combination with another famous book of hertweck, called "Der Kupferwurm" (the copper worm), a book dealing with all sorts of electrical problems and how to understand the root causes and the remedies. Unfortunately it is written in German language - good for me ...
I also thought of reversing the front brake lever at my plunger GF but have not started the activities yet. I addition, here in our country you have to get modifications like this being checked, agreed and documented in your papers by the TÜV. At least the rear brake has the lever rotation against the wheel and this brake is quite good.
Best regards, Manfred
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... I meant the Zündapp K800 which had the rear brake lever rotation with the wheel. The KS600 had it against it again. Pls apologize.
Best regards, Manfred
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My experience with drum braked cars is that its worth getting modern high friction linings fitted. Its not that expensive - I seem to recall about £80 and the improvement can be huge. Most modern linings are very hard and optimized for low wear - 100k miles plus. But on an old vehicles a brake life of 10k miles would be fine if it was 2 or 3x better at stopping.
I drive a Land Rover with TLS drums on the front and SLS on the rear. I fitted new linings when I got it and the brakes were terrible, after 10 k they weren't even bedded in and looked set for 200k. I changed to high friction, they bedded in in 100 miles and at 10k were about 10% worn but it stops like a modern car now. Do a search for someone who relines the classic race cars and bikes.
There's actually a Brexit angle to this (honest), the EU mandated the standard for aftermarket brake shoes and pads and all the parts makers follow it but to pass the linings must pass a wear test, but no friction test so blame the EU *smile*.
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Had my front shoes relined with modern material and it has made a big difference, they certainly squeal when applied with gusto!