Author Topic: Poor front brake on A7  (Read 4947 times)

Offline warmshed

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Re: Poor front brake on A7
« Reply #30 on: 13.08. 2012 13:26 »
Interesting reply,

If the pivot pin should be as close as possible to the drum, why do people say centralise the front brake with the fulcrum loosened, by applying the brake lever? On my one the brake cable is fixed to the fulcrum so surely this actually pushes it away from the drum? Should I be applying the brake with an extension on the brake plate lever rather than the brake cable?    I have tried to centralise the brake and now it does not grab but neither does it stop!.  Dave.

Offline Rocket Racer

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Re: Poor front brake on A7
« Reply #31 on: 13.08. 2012 23:00 »
Trevor,
 thanks for the more wordy response  wink2. This has turned into a very interesting thread, am still soaking this stuff in so I can get my brakes to work as reliably as possible.

The emphasis on the trailing edge of the shoe strikes a chord. given the last "floating" iron A10 shoes have sod all pad, but its all at the trailing end of both shoes.
For such a narrow shoe these were considered (in the day ;) ) very good.

Makes me wonder if an alternative to increasing the pivot pin diameter (for worn drums) is reverting to floating shoes which will always have the first contact at the trailing end.

Thanks again.
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.
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Re: Poor front brake on A7
« Reply #32 on: 14.08. 2012 11:35 »
I got "into" brakes by accident when I was at Georgre Heggie's shop @ Kingsgrove and made a derogatory comment about the "comicals" fitted to my A 65 L.
George literally grabbed me by the ear, dragged me into the workshop and showed me the brakes on his racing triples.
Then he pulled my wheels apart and showed me how it is done.
To be truthful I locked the front wheel a dozen times on the way home ( & took some short flights ) and it took me a long while to get used to brakes that works so well.
I packed packed out the pivot on the B 40 and boy did that make a difference.

Centralizing the shoes means having the pivot ends of both shoes the same distance from the drum, not making both shoes concentric with the drum and you still need to do it otherwise the cam will be pushing one shoe into the drum harder than the other and as they are both worked from different ends of the same cam if the trailing shoe hits the drum first it will stop the leading shoe making proper contact and it is the leading shoe that does most of the work.

If you really want to "tune" your brakes get shoes that have steel caps on the cam end.
Pull the caps off and fit FULL HARD SHIMS ( yes I was shouting ) under them so that both shoes make the same contact with the drum.
Use some plastigauge to measure the contact.
As was mentioned in previous thread the shoe that has the lower contact point with the cam will move faster towards the drum while getting lower braking pressure while the top cam shoe will move slower but get higher pressure.
To their shame BSA used a brake cam that is symmetrical where as to brake properly they should have used a cam that is shaped to even out this problem.
Polishing the contact area of the cam to a hight shine will make a difference as well
Bike Beesa
Trevor

Offline duTch

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Re: Poor front brake on A7
« Reply #33 on: 14.08. 2012 13:21 »
Thanks for the insights Trev, 
                                        A> because this relates to words Tim and I exchanged  a while back re; rigid  wheel operating arm up->good?,subsequent arms down->crap?, and arm length.
B> I've grafted a 'comical' on the front of my plunger, and have been analysing the product for functionality.
 Will read all that again later.
 cheers duTch
Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
Have a '74 850T Moto Guzzi since '92-best thing I ever bought doesn't need a kickstart 'cos it bump starts sooooooooo(mostly) easy
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Offline stu.andrews

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Re: Poor front brake on A7
« Reply #34 on: 14.08. 2012 16:37 »
As I started this thread, I feel that I ought to update you all. The bike is back on the road with a reconditioned magneto, so now it goes, we need to stop! After looking at the front linings, which were dry & clean, I saw that contact was being made mainly at one end of the leading lining. I roughened the linings & centralised them, to find that they are quite a bit better. I am now using mainly the front brake to get it to bed in. If, by the end of the season, this has not improved the braking to any great degree, then I shall get softer linings fitted & report again.
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2012 Triumph Bonneville SE-Fun


Offline Topdad

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Re: Poor front brake on A7
« Reply #35 on: 14.08. 2012 16:45 »
Hi guys , I've been reading this with great interest and must say that I'm still very happy with my 8" single sided but after reading Dutch's last post I must say that the best front brake I ever had on a a10 was my first plunger a10's , back when I was kid ,  with a chair attached I swear I could squeal the the front tyre in the dry and lock it in the wet ,it was set up by my brothers mate who acquired a set of "the magical green linnings " that are so often spoken of by old men with tears in there eye's!! I had my wheel off 2 weeks ago and bingo seemed the same type and still with some life left in 'em to boot. Best wishes BobH.
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Offline shuswapkev

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Re: Poor front brake on A7
« Reply #36 on: 18.08. 2012 04:01 »
next thing to work on is how to get drum brakes to work in reverse...
  \
 that has always been a mystery to me...

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Re: Poor front brake on A7
« Reply #37 on: 18.08. 2012 12:34 »
Single leading shoe brakes work equally as bad in both directions which is one reason why you never fit twin leaders on the rear axel
Bike Beesa
Trevor

Offline duTch

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Re: Poor front brake on A7
« Reply #38 on: 18.08. 2012 12:46 »
Gee Trev, I have a TLS on the back end of my Moto(it's a 'T' model), and I don't have any trouble when I'm going backwards..!!.. (italian tanks- 1 forward gear, multiple reverse)
 On the other hand, I think I know what you mean, in that the TLS doesn't work on the rear, if on the opposite side for which it's designed(opposite rotation??). Otherwise, wouldn't it be ok, that is; if it's on the correct side for rotation (on the rear)??
 cheers duTch
Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
Have a '74 850T Moto Guzzi since '92-best thing I ever bought doesn't need a kickstart 'cos it bump starts sooooooooo(mostly) easy
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Online bsa-bill

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Re: Poor front brake on A7
« Reply #39 on: 18.08. 2012 14:06 »
Hi Dutch
without going out to check my TLS (not allowed in the shed unless it's critical to fitting our new kitchen  *sad2*
but should be possible to switch the cam with the pivot
All the best - Bill
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Offline duTch

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Re: Poor front brake on A7
« Reply #40 on: 18.08. 2012 23:53 »
Sorry Bill,
             Can't see it'd work on a Beeza one, as the pivot point may be removable, but seems is cast in, and the hole would need to go right through, and the components interchangeable, which they're not.
 Also the vent would be facing backwards,unless rotated upside down, which may or may not work either way?
With other constructions it may be possible, but I don't want to get involved with that.
 However I still can't see why it shouldn't work on the rear, and am sure I've at least heard of it done, on the same side, with same relative wheel rotation??
 
 If you hadn't guessed, 'going in reverse on the Moto', was partially tongue in cheek, except for parking and a failed bump start, when I need to push it back and try again!!!
  Cheers, duTch
Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
Have a '74 850T Moto Guzzi since '92-best thing I ever bought doesn't need a kickstart 'cos it bump starts sooooooooo(mostly) easy
Australia