Author Topic: A10 rear brake travel.  (Read 181 times)

Offline Tomo

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A10 rear brake travel.
« on: 06.06. 2021 21:56 »
Hi,
I have almost reassembled my 1960 swing arm GF after a respray and new bits. Since it's been on the road for 5 years the rear brake movement is excessive. I have found posts on the forum about brake arm geometry etc which make sense.
This is more to do with no stop for downwards movement. I have set the rear brake to be just off binding in free wheel. It goes to fully on after an inch of downwards movement, but if I keep pushing down with my foot (as per an emergency stop, oh s!*t moment) the lever keeps going! Is this normal? My modern bikes all have had adjustable screws to act as a lever stop. 
I have had a search for an answer to my question to no avail. Can you help please? Thanks.

Online Billybream

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Re: A10 rear brake travel.
« Reply #1 on: 07.06. 2021 03:33 »
This is why alot of owners convert to rod arrangement, not an easy task, loads of information on here.
I tried a stop, using the foot rest and it worked okay but was not very pretty. Then decided to try a new cable, which I think 3 lengths are listed, new shoes and a play with the geometry of the levers and results are better.
1960 Super Rocket, owned since 1966, back on the road 2012 after being laid up for 29yrs.

Offline Swarfcut

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Re: A10 rear brake travel.
« Reply #2 on: 07.06. 2021 08:23 »
Tomo. The operating arm on the rear hub points up on early models and changed to pointing down (so called reversed lever/better performing) on later models. You need to make sure the cable length and run are correct for your assembly.

 The outer cable is often overlooked.  No real force will be generated on the hub lever until the outer cable windings are pressed tightly together by their initial compression on operating the pedal. Over time your cable is likely to have been kinked, stretched and otherwise abused. This movement may not be visible, but under the outer covering its like a stretched out spring and some of the pedal movement is taken up by compressing the outer cable rather than operating the brake. Like BillyB found, the whole shebang may need replacement for perfection. All depends on what is found on close examination.

 A good quality new cable of the correct type will improve matters. You need a stop to position the pedal at rest, but definitely not one to restrict downward movement. Cable brakes never have the solid feel of a rod operated system.

 Swarfy


Online BagONails

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Re: A10 rear brake travel.
« Reply #3 on: 07.06. 2021 15:47 »
Hi Tomo,

I am grappling with a similar issue on my bike currently.  This one has a rod conversion that seems to have been done quite well but there was virtually no contact between linings and brake drum when I started. (the bike is new to me). I found the hub/drum had been machined and new linings fitted and it now seems to be down to getting the shoes to bed in.

If properly set up the brake should be fully on in less than an inch of movement and this suggests there is some freedom in the system that should not be there. 

I would take things apart and check the wear pattern on the shoes and the squareness of your drum to the back plate, also check everything is centralised (the pivot pin can float when released and the wheel spindle also has an input).  Ideally there should be full contact between the shoes and the drum otherwise you will get that lost motion / spongy action. Other things that contribute are any loose fits between pivots and pins, rods through clevises wear in bushes etc etc. Operate the lever and watch all the movement checking for any lost motion i.e. instead of, or as well as, rotating the shaft the shaft moves perpendicular to its axis due to wear in the support bushing. Watch also for things twisting off or bending out of line too.

If you were preparing the brake for racing you would machine the drums true, fit oversize linings and machine them down assembled on the back plate, to just fit tightly in the drum. In this way you are aiming for full contact and minimal clearances. The brake should only improve with use... until it starts wearing out again!

Good luck with it all anyway.
Ian

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Offline chaterlea25

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Re: A10 rear brake travel.
« Reply #4 on: 07.06. 2021 16:07 »
Hi All,
Most replacement shoes have too thin a lining to get the levers and cable pull angles anywhere near correct
I got some original linings from an autojumbler at Stafford, Memory says they were 5,5mm thick ? (7/32in.)
On Another A10 I packed out the shoes with some steel strip to get the linings nearer the drum
I would think have oversize linings bonded on to the original shoes and machine to suit the drum would be the best solution ??
I also shortened the cable inner and outer to get as straight a run as possible and correct angles on the levers
The brake will lock the wheel now if required  *eek*

John

1961 Super Rocket
1963 RGS (ongoing)

Offline Tomo

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Re: A10 rear brake travel.
« Reply #5 on: 07.06. 2021 22:12 »
Funny enough the brake works fine! I can lock the rear wheel without a problem. My issue is the spongy feeling and continuous downwards travel which is disconcerting when braking quickly. I suppose it's that "not knowing what normal is/should be" issue. The lever rests nicely on the foot peg as a top stop.

I have had a real close look at everything after reading your replies. There is a lot going on when thinking about it. All tolerances on the pivot arms look fine, although from what you have said BagONails, the wear appears to be only on the front couple of inches (the shoes are fairly new). Surely that is not very efficient. I think you have hit it on the head so to speak, I did fit new shoe springs.

I have read elsewhere on this forum about filing down the profile of the shoes in order to get more contact. A mate tells me that "in the old days we used to do it all the time when fitting new shoes, get your file out lad".

How big is the usual point of contact in peoples experience? I imagine that as BagONails said that the point of contact will increase with use. This appears to be a slight design issue and why upgrades have two cams instead of 1? Thanks again for all of your help.

Online BagONails

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Re: A10 rear brake travel.
« Reply #6 on: 08.06. 2021 00:00 »
Funny enough the brake works fine! I can lock the rear wheel without a problem. My issue is the spongy feeling and continuous downwards travel which is disconcerting when braking quickly. I suppose it's that "not knowing what normal is/should be" issue. The lever rests nicely on the foot peg as a top stop.

I have had a real close look at everything after reading your replies. There is a lot going on when thinking about it. All tolerances on the pivot arms look fine, although from what you have said BagONails, the wear appears to be only on the front couple of inches (the shoes are fairly new). Surely that is not very efficient. I think you have hit it on the head so to speak, I did fit new shoe springs.

I have read elsewhere on this forum about filing down the profile of the shoes in order to get more contact. A mate tells me that "in the old days we used to do it all the time when fitting new shoes, get your file out lad".

How big is the usual point of contact in peoples experience? I imagine that as BagONails said that the point of contact will increase with use. This appears to be a slight design issue and why upgrades have two cams instead of 1? Thanks again for all of your help.

If you mean you can lock the wheel when riding the bike then you are way better off than I am with mine at present!

Yes, one of the drawbacks of single leading shoe design is exactly what you have noticed the leading shoe ie. the one facing the direction of rotation at the cam end rather than the one trailing gets the maximum self servo effect and binds on the drum whereas the trailing shoe gets the opposite effect, the drum is just brushing past and the force vectors work to take the brake off rather than on.  The ends of the shoes at the fixed pivot do the absolute minimum of work and will only touch onto the drum if everything is 100%.  You can have too much self servo actually and that is why the leading shoe is usually cut back, I don't know if you noticed that.

Having two cams or what is called twin leading shoe is certainly more effective, probably about 30% more. There are even brakes out there with 4 leading shoes or more but getting these set up to work nicely can be a real pain.

So with all this in mind, as John said getting full contact, and having the linings as close to a match on the drum diameter as possible is the best starting point and makes a big difference, something I'm still working on!
Ian

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Offline Tomo

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Re: A10 rear brake travel.
« Reply #7 on: 09.06. 2021 21:39 »
What is everyone's experience with wear on brake pads?

How much of the leading pad would you see worn/used after say 6 months use? Is a couple of inches contact normal?