Fitting a disc front end? (& clonking front brake)

[ajs-scrambler]

Hello everyone, I am the proud owner of a 16MS in scrambles trim, it's my first Brit bike to own - I used to 'borrow' my Dad's to pop down town on, trip to the pub etc but I'm finding owning one might not be as easy as I thought!

Maybe I'll put up another post about general gripes and see if you can talk me out of swapping it for a Jap bike! but for now my main fear when out and about is having to brake a bit before everyone else as the front brake isn't fantastic. Also, sometimes, as I'm coming to a halt, the front brake is applied and working but then the lever suddenly comes in a few mm more and the front end dives a little with a bottoming out sensation. I thought it was bearing play but checked and adjusted that, still does it. So I was wondering if anyone has fitted a disc brake? I did see a post on this site of a 1954 Matchless G80S with one and was going to ask the author but I can't seem to find that now.
I have general maintenance knowledge (again, Jap, so not alot required ) so in no way claim to be a fully fledged mechanic/rebuilder but I guess its gonna be a nightmare fitting to the frame, mounting h/lamp, hoping wheels are aligned, matching wheel size?

Thanks in advance....
Steve

http://www.flickr.com/photos/110973365@ ... 480027895/

[saltbox alf]

Oh dear, I hear the sound of 'worms, can of' being opened!! The drum brake's on british bike's were never up to today's standard and often if lucky might give you a slight slowing effect
Seriously, they can be made to work quite well and the thought of fitting a disk brake on a 16ms will be anathema to most!! chocking on their tiffin or porter!!

See here for a good guide to making you brakes work.
http://www.realclassic.co.uk/techfiles/ ... 92600.html

Part 2
http://www.realclassic.co.uk/techfiles/ ... 00900.html

[Rob Harknett]

A nice looking mid 1950's " special " which I am sure performs like a mid 1950's motor cycle. I guess everyone else has a modern machine ?? More gripes will confirm you are not happy with the ride a period machine gives. If out on a run with the lads with similar machines, everyone else is equal to you. You do have to take extra care in modern day traffic. Club and club sections organising runs will try to avoid fast roads. There may even be riders in the group with even older machines with brakes no better, and of the same design as a push bike. Perhaps even of the era of being push start with no gears or clutch.
These bikes being slowed down ( they don't stop ) by use of an engine decompreassor, to slow the bike. So you need to judge timing for green when approaching traffic lights, or a gap at a round a bout. An old bike will test your skills, you will enjoy taking the challenge or swap for a more modern bike.

[ajs-scrambler]

Thanks for your replies. Yes it could be a case of 'just' changing my riding style. Today's drivers do seem to leave it to the last minute to brake & I get sucked along with them, forgetting I need longer to stop. Also the bike does pull well (to me, for a Brit bike ) and has a lovely exhaust note so I am easily tempted to open that throttle perhaps a bit too wide!
I wonder if you can do advanced rider training on a classic bike?

[1608]

There are a few simple things to check first to make sure that everything is as it was originally fitted before you decide to fit modern discs to a relatively slow, by todays standards, bike. Have you had a look at the brake drum internals? The symptoms you describe sound ratrher like a badly worn cam and or the corresponding part of the brake shoe. Are the linings in good shape, not contaminated or down to the rivets. Is the brake cable the correct length, too long and the brakes can feel spongey. The forks bottoming out could be lack of fork oil or weak springs.

[Stan Palmer]

I have a similar problem to you, not experienced on these old bikes (if you discount regularly riding one 50 years ago), I don't do enough miles to become accomplished and as a result have frightening experiences due to the brake.
I bought a BMW twin leading shoe hub for mine, haven't fitted it yet (probably won't). Mentioned it to Steve Surbey, he told me he had very good results by having the drum of the fully built wheel skimmed fully circular.
There are other things people do, relieving the leading edge is one (there are threads on the forum for that)
through to fitting mini hydraulic cylinders (not sure whether as twin or single leading shoe). I would really worry about fitting a disc brake. I remember the very first one mentioned in the magazines late fifties, on a Royal Enfield, it was capable of bending the fork tubes.
The method I would like to try if I can find a spare brake plate is as used on BSA works scramblers. The brake expander was mounted on a separate outrigger bearing, bolted securely to the plate. The bolt holes were elongated so that the expander could be centred on the shoes merely by loosening the bolts, applying the brake and retightening. They were very good brakes, and the same 7" size as AMC. With that and skimming it might just be enough. Problem is there are always so many other things to do....
Stan

[SPRIDDLER]

I wonder if you can do advanced rider training on a classic bike?

One of the Sussex section members, 'Spares Dick' (Dick Somers) is a retired Police instructor and since retiring has been an advanced rider instructor. He rides only his 40's, 50's and 60's AMC bikes and is one of the organisers of past years' and next year's 'Westward Ho!' events.
I'll check with him and email details of the courses to you.

[SPRIDDLER]

The question of front brake improvement keeps cropping up.
With the brake shoes assembly out of the wheel chalk an arrow on each brake shoe in the direction of wheel rotation. (See pic) Be careful when marking the arrows as you'll be looking at the brake assembly 'back to front' i.e as a mirror image of when it's installed.
The arrow pointing away from the brake cam/expander is on the leading shoe and the arrow pointing towards the cam is on the trailing shoe.
The leading edge of the leading shoe and the trailing edge of the trailing shoe are both at the cam end of the shoes.

100_1398 (640x480).jpg

Because the fixed brake shoe pivot doesn't move when the brake is operated the cam ends of the shoes inevitably touch the drum first until the linings are 'worn in'. Hence disappointment when a relined brake performs no better or maybe worse than the old ones.

Ideally, when the brake is operated we want both shoes to contact the drum at the same time and with equal force but since it isn't easy to know that this is the case it is essential that when the brake is operated it is the leading shoe and not any part of the trailing shoe which makes first contact with the drum. This will ensure that the brake benefits from the 'servo' effect on the leading shoe as a result of the drum dragging the leading shoe outwards towards it. The trailing shoe is in effect being 'pushed away' from the drum. Now, if, upon braking, the trailing edge of the trailing shoe touches the drum before the leading shoe you lose the 'servo' effect of the drum tending to 'drag' the leading edge of the leading shoe outwards towards the drum (look at the chalk arrows). Keep up at the back, there'll be questions later.
To give an extreme and hypothetical example you could remove either of the shoes completely, refit the assembly to the wheel with only one shoe, and the brake would still work, although it would not be possible to fit the pull-off springs.
Furthermore, you also want as much area (length) as possible of both linings to contact the drum. Once one shoe (either shoe) has contacted the drum the cam will not be able to turn any more therefore you want to ensure that it is the leading (servo effect) shoe which makes contact first. Brake drum/lining skimming which matches the drum and linings contours is a further option to improve braking, especially if the wheel has been rebuilt which can have distorted the drum.
I arrived at a total of one and a half inches removed from the trailing edge of the trailing shoe by taking off about a quarter of an inch at a time (see pic), refitting the wheel and trying it out on the road. I put the shoe in a vice, hacksawed across the 7/8" width of the lining down to the shoe casting then used a chisel to carefully 'lever' or slice off the end of the lining material starting from the cut and going towards the end of the linings as I didn't want to risk disturbing the adhesion of the lining that was to remain. The amount of your lining which will need to be removed will not necessarily be the same. I would only modify the bonded, not riveted type of linings.

100_1399 (640x480).jpg

Adjusting shims can be fitted under the stems of the removable 'mushrooms' at the cam end of the shoes on some models to compensate for lining wear by bringing the linings closer to the drum when 'at rest', thus eliminating lost lever action before the linings make contact. Ordinary steel washers, trimmed to fit, of various thickness can be used here. Each shoe mushroom may need a different thickness of washer. Obviously, washers cannot be fitted on models which have the castellated type of wear adjusters.
You can also rotate the wheel on the bench repeatedly applying the brake, disassemble and look for high spots or non-contact areas on the linings. A bit of chalk dusted onto the linings can help disclose these non-contact areas and give you a clue as to what's going on when the brake is applied. You will probably be surprised at how little of the linings shows drum contact. It's worth repeating that centralising the shoes inside the drum after replacing the assembly into the wheel is essential. Do this on the bench with wheel on its side by loosening the fixed pivot, locking the brake on hard (a tube over the brake arm helps to apply sufficient force), then tightening the fixed pivot and brake backplate locking nut.
I recognise the inevitable risk of poking my head above this technically contentious parapet and it is not intended to be comprehensive, definitive nor authoritative but if it helps anyone to understand or to fettle their front brake so much the better.
There are other factors to consider; Modern asbestos-free linings are harder/have a lower coefficient of friction than the originals, handlebar lever pivot pin to nipple centre distance should 7/8", outer cable construction on some cables is flimsy etc. etc..........

[saltbox alf]

Yes it could be a case of 'just' changing my riding style.

You are halfway there with this idea, the bikes were designed for the road and traffic of the time and it's quite a different style of riding. However once you get used to the pace you will be supprised at how much you will enjoy it, the smell of the countryside , a waft of pefume from a lady on the pavement as you pass and all manner of things you would miss at a greater rush.

The feeling of acheivement after a run, man and machine in harmony. It's the pleasure of handling the machine and working within it's paramiters.

I started on these type of now, classic, bikes but for many years had 'jap' plastic rockets great fun and my last was a Kwak ZZR1100.
The principles are the same though. I have a G3ls and the smile after a run is the same as I had from the Kwak. just took a bit longer to arrive!!
Suprisingly on the question of time , It takes me an extra ten minutes to do over a 100k to reach my house in the village from my lady's house on the G3 and I am much more relaxed too.
Keep on with it you will enjoy

[Rob Harknett]

You often find the brake anchor fork bolts with damaged threads even little cracks, some are only good for scrap 50/60 years old remember. So you do need to consider, if a more powerful brake is fitted will the old anchor fitting bit up to holding on. Or will you discover the old anchor will not hold on to the fork. So you end up looking for a new fork leg, if you survive the accident.
I have a CSR lightweight fitted with a old Suzuki front wheel with drum and linings. Having only ever ridden old bikes, this is the best brake I have ever used. It's too good for my liking, so I use it very lightly. When I did once hit it hard, both myself and pillion ended up almost sitting on the tank. I've got an old original wheel to put back in it one day.