Author Topic: 8" single sided front brake  (Read 307 times)

Offline a101960

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8" single sided front brake
« on: 15.01. 2020 11:04 »
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.

Online KiwiGF

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Re: 8" single sided front brake
« Reply #1 on: 15.01. 2020 11:16 »
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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Online berger

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Re: 8" single sided front brake
« Reply #2 on: 15.01. 2020 19:13 »
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

Online Greybeard

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Re: 8" single sided front brake
« Reply #3 on: 15.01. 2020 19:27 »
Has that mod made a big difference?

Online berger

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Re: 8" single sided front brake
« Reply #4 on: 15.01. 2020 20:24 »
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*

Online RichardL

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Re: 8" single sided front brake
« Reply #5 on: 15.01. 2020 22:44 »
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.)

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Online berger

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Re: 8" single sided front brake
« Reply #6 on: 15.01. 2020 23:14 »
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

Offline BSA_54A10

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Re: 8" single sided front brake
« Reply #7 on: 16.01. 2020 00:22 »
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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Online Black Sheep

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Re: 8" single sided front brake
« Reply #8 on: 16.01. 2020 06:43 »
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...
2 twins, 2 singles, lots of sheep

Online JulianS

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Re: 8" single sided front brake
« Reply #9 on: 16.01. 2020 10:31 »

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.

Online morris

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Re: 8" single sided front brake
« Reply #10 on: 16.01. 2020 11:27 »
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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Online berger

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Re: 8" single sided front brake
« Reply #11 on: 16.01. 2020 12:34 »
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*

Offline Swarfcut

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Re: 8" single sided front brake
« Reply #12 on: 16.01. 2020 13:16 »
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.

Online morris

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Re: 8" single sided front brake
« Reply #13 on: 16.01. 2020 19:58 »
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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