Author Topic: c10 front brakes  (Read 1119 times)

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Offline steve70

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c10 front brakes
« on: September 26, 2020, 02:49:15 am »
probably an old topic, front brakes on bike have always been bad, new linings, took them off, look glazed, took all high spots off the put whole unit in and kept turning and sanding till both shoes were touching evenly , still the same not good, rear brakes do the work, oddly if the bike is pulled backwards they lock up as should, is there something simple im missing, C11 works fine and they are identical

Offline steve70

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Re: c10 front brakes
« Reply #1 on: September 26, 2020, 06:42:31 am »
 after posting had another look, found a brake arm off a A7 dropped it down to keep pull almost straight, big difference , leverage  . the A7 arm was an inch longer , the brakes now are good, and easier on the wrist,

Online Owen

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Re: c10 front brakes
« Reply #2 on: September 26, 2020, 06:57:39 am »
Many moons ago when my C10 needed a MOT. I watched as the tester did the brake test and snapped my front brake cable trying to lock the front wheel. Lucky I had a replacement to hand.  He got the front to 75 NM but not locking up and back to 105 NM which would lock up quite easily with modern linings. Therefore I ride accordingly.
1940 C12 (350cc)
1945 C10 & C11
1953 C10 & C11

Online timsdad

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Re: c10 front brakes
« Reply #3 on: September 26, 2020, 07:40:49 am »
It's how they were designed to be but, as road surfaces improved, the brake design stayed much the same for several years.

BSA brakes will work quite well once they're bedded in properly. This can  take a few hundred miles of proper use but, if the bike is stood up for a period, the bedded-in linings glaze up again and you have to start all over again.


Ray
Just a motorcyclist.

Offline BSAc11g

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Re: c10 front brakes
« Reply #4 on: September 26, 2020, 10:17:21 am »
The biggest problem with C series brakes is the linings they were designed to se are no longer made
The nest problem is most drums are way past the wear limit so the contact angles are wrong
The nest problem is no one actually understands self -servo mechanical brakes any more  and the web is full of fixes that are only applicable to power assisted brakes.

To work properly the shoe has to be machines to a slightly bigger radius that the drum
So when the leading edge of the shoe hits the drum, the rotating force of the drum is transferred to the shoe pushing it hard against the rear pivot and then causing it to flex into full contact with the drum .
For this to happen the rear of the shoe has to be very close to the drum.
This is the theory behind fully floating brake shoes .
So start with the pivot.
Most have some sort of adjustment so the shoe can be brought closer to the drum .
If not then the shoe itself usually has a slipper that can be removed & packed out to bring the shoe closer to the drum .
make sure that the operating lever on the backing plat can not get to 90 Deg to the cable
Again most BSA levers have a double square so you can move the lever with respect to the brake cam .

Have close look at the cam and the wear face of the shoe.
Both will probably be worn with a groove so the brake makes contact with the drum, the the pressure is relieved as the cam hit the wear hole .
 You want the leading shoe to travel faster so the cam should be set up so the leading shoe is activated by the outer edge of the cam & the trailing shoe the inner .
Lots of clowns who do not understand the principles tell you to do it the other wah, which is correct for power assisted hydraulic brakes, hot hand powered motorcycle brakes.
Mind you a lot of riders in the day had no idea either judging from all of the "readers tips" I see in period publications.

Then we come to the levers , cables & perches .
Almost every BSA I inspect for road worthyness has the pivot hole in both the lever & the perch worn quite oval , drastically reducing the leverage.
If yours are not round & close fitting, replace them or bush them.
And finally there are a myriad of different lengths of levers from the pivot hole to the lever ( forgot it's actual name ) .
If they are not matched you loose leverage
After that there s the cable itself and in particular the outer.
A lot of cheap ones have a open spiral wound outer which becomes a great big spring when you pull the brake lever so get good quality ones.
The most expensive brake cable is a lot cheaper than taxi fare too & from the casualty department , let alone physiotherapy every day.

The we come to proper lubrication.

Plain bowden cable should be lubricated with a dry teflon solution.
I use Tri-Lube, it comes from push bike shops & is used to lube gear change cables .
It is not cheap but a 4oz bottle will last for a decade or more.
Nylon lined cables can be lubed with the same goop or kerrosene
WD 40 must never ever get anywhere near a nylon cable and in fact has no place on a C series apart from the points.

Now to get into the esoteric stuff.
A wound cable unwinds when you stretch it .
so it must be able to rotate when pulled.
In most cases this is supposed to be done by the brake end which has a ball or pear type fitting on it ( clutch is the same )
In order to rotate the cable end and the socket it fits into must be smooth & lightly lubed .

In practice this never happens & the ball ends get mutilated causing a lot of that effort you are applying going into unwinding the inner cable.
The solution to this is to fit a floating drum to the handle bar end .

Even better if you do this the cable will last forever
Bike Beesa
Trevor

Offline steve70

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Re: c10 front brakes
« Reply #5 on: September 26, 2020, 10:23:59 pm »
Trevor
ive got quite a bit out of this, some  wear issues I have addressed,  and some not, when the bike was in pieces, I put new spokes in and skimmed the drum back to round then, it wasn that bad , the fitting arm to square is tight   the  angle with cable looks as it should,  I hadnt even given the cable a thought, it is new. nor wear on the shoes and cam. I have another bike unnamed with a similar sized front drum that locks up with little pressure , so a relook today, the longer arm made a substantial difference.

Offline BSAc11g

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Re: c10 front brakes
« Reply #6 on: September 28, 2020, 05:47:33 am »
The only BSA I have ever owned that the front could not be locked up are the girder framed ones.
I could have made them work that good as well but you really don't want a strong front brake with BSA girders.
Well perhaps a C 10 as it has very limited engine breaking capacity .
Bike Beesa
Trevor

Online timsdad

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Re: c10 front brakes
« Reply #7 on: September 28, 2020, 07:25:42 am »
Yes, a C10 has very limited engine breaking capacity - and not much engine braking either!


Ray
Just a motorcyclist.

Offline ThomasC11

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Re: c10 front brakes
« Reply #8 on: September 28, 2020, 08:43:57 am »
Hi Trevor, this is the first well justified description about this topic I have ever seen. However, I have problems to understand some details. Could you manage to make a text with some explaining pictures for our technical tips?
Cheers, Thomas
1946 BSA C11
1937 Sunbeam Model 9
... and a scratched Hyundai

Offline BSAc11g

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Re: c10 front brakes
« Reply #9 on: September 29, 2020, 08:30:27 am »
Anything that is unclear, please ask .
The current running bikes are all girders so no photos of C series brakes to upload.
Search Self energising or self servo mechanical drum brakes should bring up  lots of information with better diagrams than I could ever do .
The important thing is the speed of application rather than the force of application
Si the leading shoe should normally be activated by the outer edge of the cam on a single leading shoe brake because it moves further and there fore faster then the lower edge.

Most riders who come in with rubbish brakes have a gap between the shoe & drum you can measure in fractions of an inch
To work that gap  should be .050" tops .

Your hand can only apply a few kg of force onto the brake lever , unless you arm wrestle with Big Arnie & beat him.
Allowing a 100:1 leverage your puny wrists are not going to stop 100 Kg of motorcycle at 60 mph unless you can use the momentum to assist you.
So all you need to do is poke the leading shoe into the drum and hold it there tight enough for the drum to force the shoe to flex into the drum
Think about grinding on a bench grinder and all those times you go the angle wrong & stalled the wheel, generally taking a good size lump out of the abrasive .
The trailing shoe is only there  for stability and is not supposed to do much in the way of braking because the drum effectivly pushes the shoe away.
The only time it is doing much in the way of work is when you are on a hill pulling the brake to stop yourself rolling backwards.
I gave up writing to editors of magazines correcting rubbish they they have printed decades ago and sine the web has fired up the power of the masses means what I know to be correct is wrong , along the lines of eat schit because 200,000,000,000,000,000,000,000,000 flies can't all be wrong.
Very easy to pinch some ones pretty diagrams the do a cut & paste to make your self appear to be intelligent.
There would be almost no one alive who drove cars in the mechanical brake only days and everything published since is all based on hydraulic power assisted brakes where the pressure applied on the the shoes IS high enough to provide effective braking  force .
Bike Beesa
Trevor

Offline ThomasC11

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Re: c10 front brakes
« Reply #10 on: September 29, 2020, 09:58:16 am »
OK!

Quote
So the leading shoe should normally be activated by the outer edge of the cam on a single leading shoe brake because it moves further and there fore faster then the lower edge.

What is a "leading shoe"? What is the "outer (and lower) edge of the cam?

Quote
So all you need to do is poke the leading shoe into the drum and hold it there tight enough for the drum to force the shoe to flex into the drum

I don't get it.
1946 BSA C11
1937 Sunbeam Model 9
... and a scratched Hyundai

Offline c11jim

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Re: c10 front brakes
« Reply #11 on: September 29, 2020, 12:58:34 pm »
Hi Thomas,
In the diagram below, if the wheel is rotating in the direction of the arrow the leading shoe is the one on the left. As the drum rotates against it the friction between the drum and the shoe pulls the shoe out harder against the drum. This is called the self servo effect of the leading shoe. When Trevor refers to the outer edge of the cam I assume he means the lower edge in this diagram (that is, the edge closest to the outside of the drum).

Hi Trevor,
I think you've got the effect of the cam the wrong way around. When the brake is applied both edges of the cam move the same distance and at the same speed, but they effect each shoe differently because the outer cam edge is further from the pivot point of the shoes than the inner edge. The cam is like a small gear wheel acting on two larger gears (the shoes) with the centre of the large gear wheels being the pivot point of the shoes. The shoe being pushed by the outer edge of the cam is effectively a larger gear than the other shoe because the contact point is further from the centre. As larger gears rotate slower than smaller ones, the shoe being pushed by the outer edge of the cam will move slower than the other one. Also, as a larger gear has more torque applied to it the shoe pushed by the outer edge of the cam will have more force applied to it even though it is moving slower. So the question is, what's more important, the force applied to the shoe or how fast it's pushed out?
Jim

Offline ThomasC11

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Re: c10 front brakes
« Reply #12 on: September 29, 2020, 01:38:03 pm »
Great, Jim, that helps a lot.

A picture is worth a thousand words, indeed. That is why I try to write comprehensive explaining texts for the Technical Tips section so that this information isn't lost after a while. Especially for such tricky situations like this. and especially for non-anglophones...  ;D

As far as I now understand, this is the same effect as for modern disk brakes at front wheels which get more pressure on it. The front wheel in contact to the road is then the equivalent of the leading shoe in the drum.
 
Best, Thomas
1946 BSA C11
1937 Sunbeam Model 9
... and a scratched Hyundai

Offline steve70

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Re: c10 front brakes
« Reply #13 on: September 29, 2020, 08:18:01 pm »
As far as I can see the only adjustment on C front brake is the cable, after reading first post, checked shoes and linings probably werent thick enough, and probably making the matter worse by mating linings to drum, had another set with a thicker lining,  which cut the gap down and improved braking,also using the correct lever, so speed is a big factor, still room to improve tho. They must have been able to lock up when new, but having such a small contact area as soon as wear takes place they become a lot less effective and the rider just gets used to it. I saw that diagram posted Jim, it makes the topic easier.
The one thing that interests me is how easy and with little  effort it is to lock the front brake up pulling the bike backwards

Offline ThomasC11

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Re: c10 front brakes
« Reply #14 on: September 29, 2020, 08:49:46 pm »
You can adjust it also with the drum lever position by turning it by one position on the square cam, Steve.
« Last Edit: September 29, 2020, 08:52:53 pm by ThomasC11 »
1946 BSA C11
1937 Sunbeam Model 9
... and a scratched Hyundai