Author Topic: Useless front brake on 1947 Mk 1  (Read 2258 times)

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Offline RMA

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Useless front brake on 1947 Mk 1
« on: 20 Feb 2016 at 11:17 »
I recently acquired a post war twin.  It has a 1949 Mk III engine in a 1947 Mk 1 frame, so itís a bit of a bitsa.

Can anyone tell me how to get the front brake to work properly?  Although I believe it is all connected up properly, and the lever works smoothly and easily, there is hardly any braking.  When I first got the bike you could push it along with the front brake fully applied so I sent the shoes away to be relined.  I asked for the grippiest material they had which improved matters in that I now cannot quite push it along with the front brake fully on, but on the road it's still pretty useless.  Luckily the rear brake is pretty good.

Thanks

Offline eddie

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Re: Useless front brake on 1947 Mk 1
« Reply #1 on: 20 Feb 2016 at 16:58 »
Try undoing the front wheel spindle nut, then tighten it up again while someone applies the front brake. This will centralise the shoes and should improve the braking.

  Regards,
               Eddie.

Offline Dougiethenoo

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Re: Useless front brake on 1947 Mk 1
« Reply #2 on: 21 Feb 2016 at 14:47 »
You could also look into modifying the shoes where they seat on the top pivot bolt to allow a little "float" to correct the problem of all such drum brakes - only one shoe really does any braking.
Self-energizing brakes didn't make it mainstream until later in the 50's I think.

The attached technical article is a little long and is focused on gliders - but you'll see from the diagrams that the modification could be easily applied to the Douglas brake - and as a no-risk experiment if you can find a spare pair of brake shoes to try it with.
« Last Edit: 21 Feb 2016 at 19:41 by Dougiethenoo »

Offline RMA

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Re: Useless front brake on 1947 Mk 1
« Reply #3 on: 22 Feb 2016 at 12:41 »
Thanks for the suggestions.  I take it the front brake should be better than it is?

Offline eddie

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Re: Useless front brake on 1947 Mk 1
« Reply #4 on: 22 Feb 2016 at 14:25 »
The brake should certainly be better than that! When you had the shoes out, did you check the diameter of the brake drum? It should be exactly 7" dia - if the drum has been skimmed, you will need to either file some off the centre of the linings to aid bedding in (but be careful not to inhale the dust), or unrivet the linings and insert a shim under them to bring them out to the diameter of the drum. As I said previously, centralising the brakeplate improves the braking - in some cases it is necessary to open out the hole in the centre of the brakeplate top hat bearing with a small grinding wheel to get a little more adjustment.
  My Dragonfly is fitted with Douglas brakes the same as yours and will make the front tyre squeal if I take a good handful of the brake lever! Oh, and I'm using the non asbestos linings supplied by Friction Services of Bristol - from memory, I think the code number is 3806 for that material.

  Regards,
               Eddie.

 

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