Author Topic: BAND BRAKES  (Read 8156 times)

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Offline polly

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BAND BRAKES
« on: 04 May 2014 at 09:44 »
at last thanks to SAFTEK I now have some reasonable brakes on my AERO, but the more I read on this site advise from all the experts, which I have found very helpful!, I am still at a loss when it comes to the description, SERVO, comments that changing the lever from up, down, eliminates the SERVO? early machines were SERVO then were reversed to eliminate brake grab?, surely the band brake will only work when the band is expanded, reversing the lever will only contract the band making inoperable?
the whole concept seems simple enough, so what am I missing, to quote from HEATHCOTE, :The cam is rotated in the same direction as the wheel which forces the ends of the band apart, and so expands it, whereas the leading end is drawn closer into contact, the other end tending to be dragged off: how come? both end are forced out to contact the drum ?
please put me right  lol
regards
David

Offline RRinOz

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Re: BAND BRAKES
« Reply #1 on: 04 May 2014 at 12:17 »
David, it's just common sense. An example would be when you are wire brushing something on a bench grinder. If you apply the article to the top half of the wheel, your job will grab and kick about. The brush is trying to drag the job into the brush. If you apply your job to the bottom of the wheel the job is pushed away and you will have to apply more force to the job to keep it biting. Similarly with a lathe - apply the tool above the centre line of the job and your tool will jam. Apply it below the centre line and it won't cut properly - the job just forces the tool away. On a bike with simple brakes (one leading, one trailing shoe), the leading shoe does most of the work. The trailing shoe is being pushed away and needs more force applied. A superior brake setup is twin leading shoes. They are if you like - servo.

Offline Doug

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Re: BAND BRAKES
« Reply #2 on: 04 May 2014 at 19:07 »
David,

As you figured, it is not a matter of just changing the lever from 'up' to 'down'. What makes the Douglas band brake servo (or not servo) is if the bobbin rotates in the same direction as the wheel. If so, then when the brake is applied the drum will (via the band and links) try to drag to a slight extent the bobbin around with it. This reduces the braking effort and gives the servo effect. If the bobbin rotates in the opposite direction, the brake will try to push the bobbin back, increasing the resistance to applying the brake. How the band and link is connected to the bobbin also makes an impact, though seemingly to a lesser extent. The change in bobbin direction on the 350EW can be seen in in the brake lever changing from pointing rearward (early models) to pointing forward (later models). This indicated they were having a problem with the front brake being too aggressive, and wanted to nullify the servo effect.

Have you reviewed this post?
http://www.douglasmotorcycles.net/index.php?topic=338.msg969#msg969

And this post gathered links to all of the relevant band brake as of 2010:
http://www.douglasmotorcycles.net/index.php?topic=3503.msg12770#msg12770

-Doug

Offline polly

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Re: BAND BRAKES
« Reply #3 on: 09 May 2014 at 20:12 »
many thanks Doug,
 I have read and re read all the articles re band brakes and tried to improve on what I have, alas, to little avail!, this has also included "chucking up the drums" and taking a 10thou skim out. so, I will just have to put more miles on and" read the road "to allow for stopping , until, I hope, things improve!.
regards, david

Offline Alan

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Re: BAND BRAKES
« Reply #4 on: 10 May 2014 at 04:56 »
I raised the issue of woeful band brakes several years ago as no matter what I did such as softest linings, multiple resetting, hours of head scratching etc etc, they remained dreadful....The common feedback at the time was that they either work very well or despite all efforts they won't...
 On the grounds that personnal survival overrides originality, I refitted the internals of my B29 back brake with
Triumph single leading shoe internals and the transformation was amazing...strong, powerful but controllable braking..

Offline polly

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Re: BAND BRAKES
« Reply #5 on: 10 May 2014 at 10:30 »
WHOW! Alan,
 tell me more re the mod, I believe my life riding in traffic here in UK is worth more than my machine being authentic , when I want it to stop, it should do!, your mod seems to be the way to go!
regards David

Offline eddie

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Re: BAND BRAKES
« Reply #6 on: 10 May 2014 at 11:02 »
David,
          I see from one of your previous postings that you have had the drums skimmed - have you shimmed out the linings by the same amount? If not, then the geometry of the operating bobbin and the link will be altered and could be the cause of the poor braking. I am using the standard Douglas band brake on my vintage sprint bike and it doesn't cause any worries bringing the bike back down from 100+ mph. When I relined the band, I riveted and Araldited the band in place - the rivets doing their usual job and the Araldite taking up any sponginess between the band and the lining. This is all with the early type spun steel brakedrums - later Aero type cast iron drums should give even better braking.
  Regards,
               Eddie.

Offline polly

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Re: BAND BRAKES
« Reply #7 on: 11 May 2014 at 16:09 »
Eddie, it was you ,as you may recall, advised me to use green gripper (or the type number) from saftek, and what a good piece of advise that was, I had it fitted to two of my other machines, and for the first time in ??? years, I achieved really good brakes!, well that was on the others, the Douglas?, no, with all the settings I have tried, skimming drums and re jacking the centralising screws, still a very poor brake,!!it does appear as though the front band is mounted with the hooks looking inwards, but the pin configuration, and bobbin levers are right according to the drawing,
regards David

Offline Ian

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Re: BAND BRAKES
« Reply #8 on: 12 May 2014 at 04:32 »
I have had no real issues with the band brakes on the OC or the E28. the key is to make sure you have the right backing plates for the model - for example the OC has its brakes on the opposite side to the EW. I have found that particular attention to the band/drum clearance is important. I can lock both wheels on the OC easily - can't ask for better than that.

Offline Alan

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Re: BAND BRAKES
« Reply #9 on: 12 May 2014 at 06:42 »
With the B29 building up a fair head of steam, I was riding with teeth (and other parts) firmly clenched...so decided to fit  a 50's
Triumph brake with linings part worn but usable..basically the brake band pivot point became the fixed pivot for the single leading
shoes and the Triumph rotating cam moved to the rear...to strengthen this area as the pivot arm imposes additional stresses and sticks out about 1 in I added an external plate to provide additional strength...then utilising the Triumph lever just a longer rod to the footbrake was needed...If I had machine tool expertise then making a new backing plate with internal strenthening lugs would have been a way to go and not that complicated....Works very well ( especially considering the number of bike riders in my local club who have had accidents on club runs)

« Last Edit: 12 May 2014 at 23:07 by Dave »

Offline polly

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Re: BAND BRAKES
« Reply #10 on: 15 Jul 2014 at 09:07 »
well! after many weeks of soul searching I decided to take up the advice that Allan suggested, and that was to fit triumph shoes and brake cam, attached are some pics of the mod, the gusset plate on the outside is a mod I used many years ago on my HRD to stiffen the back plate, I have also added a plate to the inside, the brake plate is still retained by a removable pin that goes in the original position in the fork leg, lined shoes by SAFTEK with green gripper material, the improvement is unbelievable!!, thanks to all the advice I have been given, now to adopt Allan's mod to the back wheel and I will have a bike that doesn't look to far away from original, and is safe to ride!.

Offline carcrank

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Re: BAND BRAKES
« Reply #11 on: 06 Sep 2014 at 14:16 »
I'm keen on this idea, but not keen on modifying my EW backing plates.  Would it be possible to use the backing plate from something else and mod them to fit the Douglas so then you still have the originals.

Cheers

Mark

Offline RockDr.

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Re: BAND BRAKES
« Reply #12 on: 07 Sep 2014 at 00:21 »
Mark if you check the ebay sales section a backing plate is for sale.......not mine by the way.

Offline cardan

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Re: BAND BRAKES
« Reply #13 on: 07 Sep 2014 at 05:12 »

Now you've got the brakes sorted, time to toss out that crap sv engine and get something with a bit more poke? Maybe a Triumph twin? A TZ Yamaha race engine? Endless possibilities.

Yes I know I'm stirring, but I've decided to speak up on behalf of the nearly-100-year-old machinery some of us are playing with. "Treat us with respect!" say their little voices. In the opening sentence of this thread was the statement "I now have some reasonable brakes on my AERO", and two other posts describe "servo" brakes with very good performance. The brakes were good enough for 100mph solos on the Isle of Man, let me guess with some careful attention they can be more than adequate for riding safely, at reasonable speed, on quiet country roads. Even in 2014.

Now I know the arguments that will come in return; they're scattered through the posts above. "With the B29 building up a fair head of steam, I was riding with teeth (and other parts) firmly clenched...so decided to fit  a 50's Triumph brake". "I believe my life riding in traffic here in UK is worth more than my machine being authentic , when I want it to stop, it should do!" An alternative might be to get your bike running and stopping as it was in the 1920s, and then riding it in the mode acceptable when it was new. This may mean slowing down a bit if you're on a sv Douglas. If this is not OK, but you still want to enjoy vintage motorcycling, perhaps you need something like an OHV BSA Sloper which offers both excellent brakes and performance.

Let's stop all this brake mod nonsense before the Douglas Servo brake goes the way of the BTH pancake generator.

Cheers

Leon

Offline eddie

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Re: BAND BRAKES
« Reply #14 on: 07 Sep 2014 at 07:40 »
Bravo Leon,
                   It's good to know there are others out there that look upon a bike's shortcomings as something that contributes to it's character, rather than being looked upon as a 'fault'! If the brakes aren't too special, learn to take 'avoiding action' and ride around the obstacle, rather than plough straight into it - the handling of most Douglases is easily up to the task. A similar scenario occurred in the 60's when Don Rickman took a Mettise to America for a dessert race - they told him the 275 front tyre (Americans favoured a 400 tyre) wouldn't stand the punishment of hitting the rocks along the way - Don's reply was "but with this tyre, I can steer around them"!
      Getting back to the Douglas brakes - they will work, provided the operating mechanism is kept in good condition and properly lubricated, rather than being neglected until that exciting moment when they are put to the test. Even my Dragonfly with standard Douglas brakes has been known to get the front tyre squealing when the need arose! - the controlling factor seems to be the level of panic within the rider!!!

  Regards,
               Eddie.

Offline carcrank

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Re: BAND BRAKES
« Reply #15 on: 08 Sep 2014 at 01:39 »
OK Leon, I was just asking.

Is this "Green Gripper" or equivalent available in Australia?  The current lining on the front (The back is OK) although apparently adjusted close to the drum at all points, has no bite at all.

My drum has some run out but being steel what can you do? (apart from riding slower)
 
Cheers

Mark

Offline Doug

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Re: BAND BRAKES
« Reply #16 on: 08 Sep 2014 at 04:01 »
Mark,

You can skim a very slight amount out of the steel drums, but obviously it is very limited; say perhaps 0.010 inch. How much run out does it have? On pitted drums I have cut the rim off and welded on a new piece of heavy wall tubing. this is then skimmed on the inside and outside diameters to true it up.

If the lining is not gripping, is the lining or the drum glazed? Might just need the glaze scuffed off, and the linings de-greased. However that will not resolve the run out.

-Doug

Offline carcrank

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Re: BAND BRAKES
« Reply #17 on: 09 Sep 2014 at 00:17 »
Thanks Doug,

I have scuffed the drum, how do you suggest I degrease the shoes? They don't look like they are oily, that's why I thought of trying some new known lining material.

Cheers

Mark

Offline Doug

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Re: BAND BRAKES
« Reply #18 on: 09 Sep 2014 at 02:05 »
Mark,

You can boil them in detergent (laundry detergent works well) or soak them in brake cleaner solvent. Or both! You could try warming them up in the oven first to see if they sweat any oil. If not, they might not need de-greasing.

The linings can get glazed too, so give them a scuff. Mind the dust.

You can of course re-line the bands with the modern (asbestos-free) woven material. But it takes some care to avoid distorting the bands. It is best to glue up the bands and material while expanded inside the drum. The bond is so strong that if the lining is glued on with the bands out of round, the lining exerts a strong force to keep the bands from evenly contacting the drum. Often you find that you still need to take a truing cut across the lining to get them perfectly round. Given the trouble to get it right, it is worth some effort to see if you can not get the original linings to work as by now they ought to be well settled to the shape of the drums.

-Doug

Offline carcrank

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Re: BAND BRAKES
« Reply #19 on: 30 Sep 2014 at 13:01 »
At RockDr's suggestion I have bought the backing plate and band on Ebay, just on the off chance they may just fit and work better than the one  that I have, however on inspection the new ones have 4 adjuster screws and my old ones have 3 (placed at 90 degree intervals) the band is the same.  I think having 4 will give it a better chance of keeping the band close to the drum and I assume a modification on bikes later than my 1928?  Unfortunately 2 of the adjusting bolts are sheared off as they are rusted solid, of course they are the usual challenging Douglas size maybe 3/16" X 27tpi in the next couple of days I should have it sorted so will see if only changing the backing plate will improve the performance.  Photo attached.

Cheers

Mark