The BSA A7-A10 Forum

Technical => Frame => Topic started by: stu.andrews on 19.04. 2012 08:56

Title: Poor front brake on A7
Post by: stu.andrews on 19.04. 2012 08:56
I have a 1961 A7. The rear brake is really effective but the front is poor. I wish to keep the bike as original as possible so do not want to go down the TLS route. Can anyone suggest some good linings that would help. The front hub has no ovality.

Thanking you.
Title: Re: Poor front brake on A7
Post by: Goldy on 19.04. 2012 09:12
Have you got it adjusted correctly, tightening the adjuster until it,s binding then just free it off a little.
Title: Re: Poor front brake on A7
Post by: stu.andrews on 19.04. 2012 09:33
Yes, all set up OK. Initial application gives a bit of "bite" but then rapidly fades.
Title: Re: Poor front brake on A7
Post by: fido on 20.04. 2012 11:45
Sorry if I'm stating the obvious but bikes of this era usually had poor brakes compared to modern machines. You won't eliminate fade entirely but there are ways of optimising the performance of the humble  sls brake. There are specialist firms advertising in the classic bike mags who will fit better linings and machine them on the brake plate to match your drum.
Title: Re: Poor front brake on A7
Post by: Pete Gray on 20.04. 2012 13:09
I've just had my A7 brakes relined by a local, Sheffield, Company.
http://www.custombrakes.co.uk/brake-pads-sheffield.html
I asked for softer linings than the existing ones which up to now have improved matters considerably.They charged £20 a pair.

But as Fido says there is absolutely no comparison with modern bike brakes.
Title: Re: Poor front brake on A7
Post by: stu.andrews on 20.04. 2012 14:01
Have had classics before but this front brake is particularly poor. Will try ferodo & your suggestions.

Thanks
Title: Re: Poor front brake on A7
Post by: Triton Thrasher on 20.04. 2012 18:01
If the trailing shoe touches the drum before the leading one, you'll have bad brakes.
Title: Re: Poor front brake on A7
Post by: huddie on 27.04. 2012 10:20
Hello Stu, I have an identical problem with the SLS front brake on my A10. Accepting all the advice about the performance of old style brakes compared with new I would say mine is frightning and I dont scare that easily. I would be very interested in how you got on with the advice.
One reply said they will be poor if the trailing shoe touches first. How does one check that then?
Regards Chris
Title: Re: Poor front brake on A7
Post by: stu.andrews on 27.04. 2012 17:21
'Tis really a case of slackening the fulcrum pin (or pivot), applying the brakes as firm as possible & retightening the pin again. This centralises the shoes. I have already tried this, so it's probably new linings next. At the moment, the magneto is off to go to be rebuilt, so when it's all back together & running I can investigate further. Watch this space!!.
Title: Re: Poor front brake on A7
Post by: huddie on 26.06. 2012 16:30
Hi Stu, Hope you pick this post up. I have just got round to sorting my front brake out, long ride coming up in July. I am still not sure what you mean by your last post. What is the Fulcrum pin??. Is it the brake operating arm attached to the drum or do you mean the brake torque arm attached to the fork leg. Sorry to be a pain but it's better to say I dont understand than assume.
Regards Chris.
Title: Re: Poor front brake on A7
Post by: a10gf on 26.06. 2012 16:44
Quote
What is the Fulcrum pin??
It's the brake shoes' 'anchoring point' at the opposite side of the brake torque arm. Needs to be slackened, then apply brakes, then retighten, ref. stu.andrews's 27.04 post.
Title: Re: Poor front brake on A7
Post by: Triton Thrasher on 26.06. 2012 17:34

One reply said they will be poor if the trailing shoe touches first. How does one check that then?
Regards Chris

One clue is the brake works better when you push the bike backwards, than forwards.
Title: Re: Poor front brake on A7
Post by: huddie on 27.06. 2012 10:10
Like I said ,I keep on asking questions if I am not sure. The only thing opposite the brake torque arm on my hub is the brake shoe adjuster. Is this what you mean by "anchoring point". I want to be sure I have this right.
Regards Huddie.
Title: Re: Poor front brake on A7
Post by: a10gf on 27.06. 2012 11:18
Yes, it's the fulcrum pin, to centralize the shoes loosen the nut, following the instructions given in posts here.
Title: Re: Poor front brake on A7
Post by: stu.andrews on 27.06. 2012 14:37
Hi Huddie

The fulcrum pin is the common pivot to both shoes, opposite from the operating cam.
Not much of an update at the moment as the bike has had a holiday whilst the magneto is being overhauled. When all is back together, I'll update the brake situation. For what it's worth, I slackened the fulcrum pin, pulled the brakes on really tightly then tightened everything, but the brakes were very little better. I expect that the linings are quite old & could do with replacing. Meanwhile, the rear is about the most powerfull I have ever had on a classic!
Title: Re: Poor front brake on A7
Post by: stu.andrews on 27.06. 2012 14:41
Huddie

You said that you sorted your front brake out- what did you do?
Title: Re: Poor front brake on A7
Post by: huddie 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
.
Title: Re: Poor front brake on A7
Post by: stu.andrews on 27.06. 2012 16:51
Best of luck with the road test- let us all know how it goes (& stops!).
Title: Re: Poor front brake on A7
Post by: muskrat 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
Title: Re: Poor front brake on A7
Post by: huddie 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
Title: Re: Poor front brake on A7
Post by: huddie 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
Title: Re: Poor front brake on A7
Post by: Jules 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)????
Title: Re: Poor front brake on A7
Post by: Rocket Racer on 11.08. 2012 22:56
thought this article was pertinent:
http://www.engineeringinspiration.co.uk/drumbrakes.html (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...

Title: Re: Poor front brake on A7
Post by: muskrat on 11.08. 2012 23:59
 That's a good link RR. I find I learn something every day here.
Cheers
Title: Re: Poor front brake on A7
Post by: a10gf on 12.08. 2012 00:08
Rocket Racer, great link indeed. +1
Title: Re: Poor front brake on A7
Post by: Jules on 12.08. 2012 07:55
Agree RR thats a really good easily read summary!
Title: Re: Poor front brake on A7
Post by: BSA_54A10 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.
Title: Re: Poor front brake on A7
Post by: Rocket Racer 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!
Title: Re: Poor front brake on A7
Post by: Rocket Racer 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
Title: Re: Poor front brake on A7
Post by: BSA_54A10 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.
Title: Re: Poor front brake on A7
Post by: warmshed 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.
Title: Re: Poor front brake on A7
Post by: Rocket Racer 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
Title: Re: Poor front brake on A7
Post by: BSA_54A10 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
Title: Re: Poor front brake on A7
Post by: duTch 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
Title: Re: Poor front brake on A7
Post by: stu.andrews 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.
Title: Re: Poor front brake on A7
Post by: Topdad 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.
Title: Re: Poor front brake on A7
Post by: shuswapkev 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...
Title: Re: Poor front brake on A7
Post by: BSA_54A10 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
Title: Re: Poor front brake on A7
Post by: duTch 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
Title: Re: Poor front brake on A7
Post by: bsa-bill 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
Title: Re: Poor front brake on A7
Post by: duTch 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