The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => Frame => Topic started by: PatM20 on 22.03. 2018 10:23
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Hi
Should the brake operating arm point upwards i.e. the cable running above the swinging arm, or downwards with the cable running below.
I have seen pictures with either routing and was wondering which was best.
Regards
Pat
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Hi
They are different Hubs. So it depends on what you have. I would like an upwards one as I think they look better.
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Thanks for this.
I will try and upload a picture.
Regards
Pat
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Hi patM20. Mine runs below the swing arm. That was how it was fitted when I bought it. ( 1960 A10 )
ELLIS
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Here's a pic of mine. Jan 1960 unrestored Golden Flash. I believe BSA changed it on earlier models from up to down - whichever, the run of the cable needs to line up nicely with the cable lug welded on the frame.
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Thanks for all your responses.
I have worked out that it only fits one way and that is down.
Regards
Pat
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Thanks for all your responses.
I have worked out that it only fits one way and that is down.
Regards
Pat
Here's a pic when mine was cable operated.
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Hi Roy
I couldn't see on the picture where the torque arm is fitted.
I thought that the torque arm was fitted to the cable adjuster mounting.
Regards
Pat
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Hi Roy
I couldn't see on the picture where the torque arm is fitted.
I thought that the torque arm was fitted to the cable adjuster mounting.
Regards
Pat
Torque arm marked in red.
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For what it's worth (and out of my realm), I was led to believe that the Rigid models had the rod on the upside and it worked better than the subsequent under-slung rod brakes...due to the way the cams activate the leading/trailing shoes. *dunno*
I tried it on my Plunger Flacket (Flash-Rocket), but the way the suspension operates it rendered it insane, as I expect would happen with a rod operated Swing-arm brake. A cable operated brake *may* work better on the top... more*dunno*
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My brake plate only has three machined holes: one for the cam/brake arm, second for the pin at the other side of the shoes, third for the cable adjustment housing.
Looks like I can only fit it down, with the torque arm attached to the cable adjustment housing.
Regards
Pat
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Yeah- just sayin', it's waaay outta my league
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As I said there are two different rear full width hubs. The bottom pull has three holes lever, pin and adjuster torque arm in one at the bottom. The top pull has an extra hole at the top for the adjuster. I think it was only about for one year. See pic below of a top puller
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For what it's worth (and out of my realm), I was led to believe that the Rigid models had the rod on the upside and it worked better than the subsequent under-slung rod brakes...due to the way the cams activate the leading/trailing shoes. *dunno*
I tried it on my Plunger Flacket (Flash-Rocket), but the way the suspension operates it rendered it insane, as I expect would happen with a rod operated Swing-arm brake. A cable operated brake *may* work better on the top... more*dunno*
Like you Dutch I really struggled that with a SLS type brake there is the “leading shoe should contact first theory” and diagrams on the net of this theory did not help me. I eventually figured it out (I think).
What bugged me most was reading that BSA racers commonly “reversed” brake levers to improve braking, which seems such a simple mod it makes you wonder why BSA did not get it right as standard!
This probably won’t make sense but I’ll give it a go!
it’s a fact that the cam contact point with each shoe happens such that one shoe contact point is further away from the spindle than the other. Ideally the setup of the brake lever should result in the leading shoe being contacted by the part of the cam that is nearest the spindle.
The reason for this is that the shoe with the cam contact point nearest the spindle moves outwards more than the other shoe, and you want the leading shoe to move more, and so contact first.
If the trailing shoe moves out further than the leading shoe then it will contact the drum first and potentially stop the cam moving, and hence stop the leading shoe even touching the drum.
It is generally understood that the leading shoe provides (say) 75% of the braking force, the trailing shoe only 25%, so if the trailing shoe contacts first then you are missing out on up to 75% of your braking power.
I did an experiment where (on a pretty poor 8” front brake) I built up the leading shoe flat cam bearing face by about 1mm with some weld, this meant the leading shoe HAD to contact the drum first even though the brake arm was the wrong way round on this particular brake set up. The result was a brake that really worked well. So my next job is to reverse the brake arm because I now know from my experiment that doing that will make the brake work better and stay working better, whereas with the experimental shoe mod the leading shoe will wear and the brake return to being rubbish.
My apologies if anyone reads this and it still does not help. I tried!
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Sorry to keep this thread running, but I expected the lining on my brake shoes to be "offset" i.e. the gaps from the end of the lining to the pivot points of the shoe to be longer one end when compared to the other end of the shoe.
However, they seem to be of equal distance. Which in my mind (small and getting smaller) means that the leading shoe wont really bite.
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Dug this out of my notes - cribbed it from the web at sometime. Maybe some help to you.
By-the-way, my swingarm GF is Jan 1960 and has the type of 8" front shoes shown in the pic, my rears are 7" QD hub and these have no leading edge.
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That graphic is very useful, thanks.