Author Topic: Poor front brake on A7  (Read 4942 times)

Offline stu.andrews

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Re: Poor front brake on A7
« Reply #15 on: 27.06. 2012 14:41 »
Huddie

You said that you sorted your front brake out- what did you do?
2010 Yamaha TDM 900-Touring
2012 Triumph Bonneville SE-Fun


Offline huddie

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Re: Poor front brake on A7
« Reply #16 on: 27.06. 2012 16:43 »
Hi Stu, What the post was meant to convey was that I am about to try and sort it out. Today I have gone through the shoe centralization process as outlined by you and others. The road test of this is still to come. What I have also done is to move the brake operating lever closer to the handle bar (small hands) so as to get a bit more leverage. I did this by slackening off the cable and then inserting a spacer about 4mm wide over the cable between the lever and the fixed mount and then readjusting the cable.
Regards Huddie
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Offline stu.andrews

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Re: Poor front brake on A7
« Reply #17 on: 27.06. 2012 16:51 »
Best of luck with the road test- let us all know how it goes (& stops!).
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2012 Triumph Bonneville SE-Fun


Online muskrat

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Re: Poor front brake on A7
« Reply #18 on: 27.06. 2012 21:27 »
 G'day Huddie,
                   you mention brake shoe adjuster so I assume you have Ariel type hubs with the 1/2" sq where the fulcrum pin is on others. Bit of a chore to set up right but good when done. Trial & error. I set up with adjuster backed off and adjust cable to give a little play, then wind in adjuster till the shoes just rub. Then it's trial with more cable/less adjuster or vise versa till I'm happy. I also added an inch to the brake arm.
Cheers
'51 A7 plunger, '57 A7SS now A10CR, '76 XT500, '77 AG175 '83 CB1100F, '81 CB900F project.
Australia
Muskys Plunger A7

Offline huddie

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Re: Poor front brake on A7
« Reply #19 on: 28.06. 2012 09:10 »
Hi Muskrat, Now I understand why I didn't understand. Proves the point that no matter how daft you look or sound, keep asking the questions. I will give your method a try. Cheers mate.
Regards Huddie

Offline huddie

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Re: Poor front brake on A7
« Reply #20 on: 09.08. 2012 18:42 »
Hello All, Finally got the road test done today on my front brake. Got to say it's much better now I have centralised the shoes. Never going to throw me over the bars though but definitely better,feels like it's got quite a bit more bite than before.
Also moving the lever closer to the bars with the spacer helped get better leverage (small hands).
Maybe new softer shoes when it's laid up for the winter.
Regards for now Chris

Offline Jules

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Re: Poor front brake on A7
« Reply #21 on: 10.08. 2012 03:46 »
Really interesting read on the brakes in this thread. I felt I had to comment after Huddie's last comment. I wont be in any position to check my brakes for quite a while to compare my feelings with years past, but I do remember nearly dropping my A7 in my teens because the front brake was really good. I have a distinct memory of braking really hard (with my then to be wife on pillion too!) and sliding forward right over the top of the tank and almost losing it. That doesn't sound like the braking performance that people are talking about in here, maybe the linings have changed dramatically over the years (non asbestos etc) I cant see that anything else would have changed (assuming they are setup correctly, as you say in the thread)????

Offline Rocket Racer

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Re: Poor front brake on A7
« Reply #22 on: 11.08. 2012 22:56 »
thought this article was pertinent:
http://www.engineeringinspiration.co.uk/drumbrakes.html

Most of the BSA brakes are fixed pivot, although the very late A10's had floating shoes with even less pad to reduce grabbing. The pivot point is identical, only the shoes are different at the pivot end and have the asymmetric pad attachment.

while these brakes will never compete with modern ones, getting them correctly adjusted and using the best pad materials certainly helps. A common refrain is that the brakes were much better before they were relined...

I'm no expert but the variations you see between similar brakes can be huge and can't be simply blamed on all SLS simply being rubbish. Well worth garage tinkering time...

A good rider periodically checks all nuts and bolts with a spanner to see that they are tight - Instruction Manual for BSA B series, p46, para 2.
New Zealand

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Re: Poor front brake on A7
« Reply #23 on: 11.08. 2012 23:59 »
 That's a good link RR. I find I learn something every day here.
Cheers
'51 A7 plunger, '57 A7SS now A10CR, '76 XT500, '77 AG175 '83 CB1100F, '81 CB900F project.
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Muskys Plunger A7

Offline a10gf

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Re: Poor front brake on A7
« Reply #24 on: 12.08. 2012 00:08 »
Rocket Racer, great link indeed. +1

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Offline Jules

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Re: Poor front brake on A7
« Reply #25 on: 12.08. 2012 07:55 »
Agree RR thats a really good easily read summary!

Online BSA_54A10

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Re: Poor front brake on A7
« Reply #26 on: 12.08. 2012 11:53 »
Just a word of warning about the article.
It is specific to hydraulic power assisted brakes.
Most of our mechanical brakes are self serving so they need to contact differently in order to grab.
Bike Beesa
Trevor

Offline Rocket Racer

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Re: Poor front brake on A7
« Reply #27 on: 13.08. 2012 02:18 »
Just a word of warning about the article.
It is specific to hydraulic power assisted brakes.
Most of our mechanical brakes are self serving so they need to contact differently in order to grab.

Have seen two hydraulic front brake drum conversions on classics (one on an ariel, the other on an M21), both were very effective. That is something I would love to do one day!
The M21 had a nice strong steel brake plate, the Ariel I don't recall.
Very common mod front and rear on racing sidecars in the day.
Lose the spongey cable from the front and rear!
A good rider periodically checks all nuts and bolts with a spanner to see that they are tight - Instruction Manual for BSA B series, p46, para 2.
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Offline Rocket Racer

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Re: Poor front brake on A7
« Reply #28 on: 13.08. 2012 05:33 »
Just a word of warning about the article.
It is specific to hydraulic power assisted brakes.
Most of our mechanical brakes are self serving so they need to contact differently in order to grab.

excepting our brakes are lifted by a rotating cam that lifts each shoes slightly differently, can you expand on how hydraulic brakes differ conceptually? Information on such topics in a readable form is hard to come by.
Obviously hydraulics can apply more force and for that matter if the anchor points are broader to coincide with the width of the hydraulic lifter that will alter the degree of servo assistance ie the point grabbing occurs but beyond that...
Tim
A good rider periodically checks all nuts and bolts with a spanner to see that they are tight - Instruction Manual for BSA B series, p46, para 2.
New Zealand

Online BSA_54A10

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Re: Poor front brake on A7
« Reply #29 on: 13.08. 2012 12:42 »
Where to start.

You need to chase up brake articles from pre WWII cars which did not have power assistance or even better the vehicles that had mechanical linkage brakes and not hydraulic braking systems.
Just about every thing you will find on the web will be about "modern" brakes.
There is some good stuff in the Victory library which I would presume you have already read.

A mechanical brake needs to bite into the drum so that the rotation of the drum dragges the shoe tighter into the drum, much like a drum clutch.
It is called the self servo action .
Our shoes should be radiused larger so that they touch at each end but not in the middle.
The leading end bites into the drum which pushes the shoe in the direction of rotation flexing the entire lining into contact with the drum.
Your brake lever effort is basically to stop the shoe skipping off the drum ( as the article stated ) not forcing the shoe into the drum.
This is the action of the leading shoe.

The trailing shoe is a different animal.
The only thing that applies any braking effort is your hand and that is bugger all when you consider what your grip strength is even allowing for the multiplying effect of the various levers

The trick to get your brakes to work better is to get the the rear of the shoe as close to the drum as you can.
the position of the rear end of the shoe determines what the radius of the shoe needs to be in order to bite but not grab or skip ( as per the article )

Note this applies to fixed shoes only.
With floating shoes it is not quite the same.

The biggest problem with our bikes now is that the drums have all worn so the angles between the shoes & drums will be all wrong to obtain the greatest efficiency.
For street use I shim at the the pivot. Others replace the pivot with a bigger diameter one and modify the shoes to fit to move the back end of the shoes closer to the drum.
Now a word of warning here as well.
Our shoes have no retaining pins so the only thing stopping the shoes twisting is the flange on the pivot and cam ( if it has one ).
For racing you will also need to consider the stiffness of the backing plate which will also flex particularly if it has a single anchor strap.
If the shoe decided that twisting off the pivot while you are under heavy braking  is the path of least resistance the results will not be pretty.
Bike Beesa
Trevor