SA front drum brake conversion

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Phileas
Posts: 226
Joined: 18 Feb 2009, 6:12pm
Location: Bristol

SA front drum brake conversion

Postby Phileas » 22 Dec 2019, 11:30am

Partly out of curiosity, I’m going to covert my commuting bike from disc brake to drum but I currently have a carbon fork which I assume is unsuitable so I’ll have to replace it - perhaps with a Surly Long Haul Trucker.

I did however wonder if it would be feasible (or sensible) to bolt an adaptor on to the existing disc brake mount to take the reaction arm clip?

Brucey
Posts: 36851
Joined: 4 Jan 2012, 6:25pm

Re: SA front drum brake conversion

Postby Brucey » 22 Dec 2019, 4:17pm

I think you could indeed adapt the mountings, but a different fork would be the best thing for sure.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

cycle tramp
Posts: 609
Joined: 5 Aug 2009, 7:22pm

Re: SA front drum brake conversion

Postby cycle tramp » 24 Dec 2019, 3:01pm

If you scroll to the end of this forum thread https://forums.mtbr.com/brake-time/stur ... 38059.html there should be a photo showing that one of the contributors has simply bent the hub's torque arm, so that it sits next to the disc brake mount, then cut off the rest of torque arm, leaving the stump, drilled a hole in it and then used a quick release saddle bolt to attach the stump of the torque arm to the disc mount.
..sadly there's not much in the way of information about how successful this method of mounting a drum brake is.

Phileas
Posts: 226
Joined: 18 Feb 2009, 6:12pm
Location: Bristol

Re: SA front drum brake conversion

Postby Phileas » 24 Dec 2019, 3:22pm

Look like he’s sawn it off and secured it through the upper calliper mounting hole.

I probably won’t be doing that. :shock:

cycle tramp
Posts: 609
Joined: 5 Aug 2009, 7:22pm

Re: SA front drum brake conversion

Postby cycle tramp » 27 Dec 2019, 9:33pm

...the engineering applied to the conversion did look a bit brutal....
Hope you don't mind me asking, are you going for a simple front drum brake or having one with a dynamo hub?

Phileas
Posts: 226
Joined: 18 Feb 2009, 6:12pm
Location: Bristol

Re: SA front drum brake conversion

Postby Phileas » 27 Dec 2019, 9:54pm

Just a brake, for now.

If I get on with it, I have another bike so a future purchase may include a dynamo hub.

Phileas
Posts: 226
Joined: 18 Feb 2009, 6:12pm
Location: Bristol

Re: SA front drum brake conversion

Postby Phileas » 31 Dec 2019, 4:21pm

I intend to use the hub brake with a drop bar lever, however, the supplied cable is not suitable. It has a nipple both ends and there is no barrel clamp included.

So I need some kind cable stop to go on the cable end. An SA one is mentioned in this post viewtopic.php?t=109134#p1053581 but I don’t know where to purchase one.

Brucey
Posts: 36851
Joined: 4 Jan 2012, 6:25pm

Re: SA front drum brake conversion

Postby Brucey » 31 Dec 2019, 4:47pm

you need part HSK770; at one time this was supplied with every new hub in the parts kit. In addition you will need a new inner cable, of course.

You can buy HSK770 from SJS, Practical cycles, or any LBS with an Ison's account, amongst others.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

Phileas
Posts: 226
Joined: 18 Feb 2009, 6:12pm
Location: Bristol

Re: SA front drum brake conversion

Postby Phileas » 31 Dec 2019, 4:57pm

Found it. It was hiding in the box. :oops:

cycle tramp
Posts: 609
Joined: 5 Aug 2009, 7:22pm

Re: SA front drum brake conversion

Postby cycle tramp » 3 Jan 2020, 6:55pm

Happy New Year! Have you fitted the brake, yet? And if have can I ask how you found it, and do you have any photos?

nigelnightmare
Posts: 625
Joined: 19 Sep 2016, 10:33pm

Re: SA front drum brake conversion

Postby nigelnightmare » 3 Jan 2020, 8:47pm

cycle tramp wrote:If you scroll to the end of this forum thread https://forums.mtbr.com/brake-time/stur ... 38059.html there should be a photo showing that one of the contributors has simply bent the hub's torque arm, so that it sits next to the disc brake mount, then cut off the rest of torque arm, leaving the stump, drilled a hole in it and then used a quick release saddle bolt to attach the stump of the torque arm to the disc mount.
..sadly there's not much in the way of information about how successful this method of mounting a drum brake is.


It might look a bit brutal but it would work OK, after all the single sided hubs X-SD/XL-SD only have a short torque arm & they work fine.

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SimonCelsa
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Joined: 6 Apr 2011, 10:19pm

Re: SA front drum brake conversion

Postby SimonCelsa » 4 Jan 2020, 6:29am

Does the orientation of the drum braked hub make any difference? Can you fit the reaction arm to either fork or is there a specific set up?

How easy is it to remove the front wheel with this set up, for instance to repair a puncture. It seems like the SA hub has a 'slide fit' reaction arm and hence it would just need some means of swiftly removing the cable from the hub to facilitate.

Just a couple of questions before I consider the purchase.

Cheers

Brucey
Posts: 36851
Joined: 4 Jan 2012, 6:25pm

Re: SA front drum brake conversion

Postby Brucey » 4 Jan 2020, 6:54am

SA have made various models over the years but with current versions for bicycles the brake plate always goes on the left of the bike. The front brake has a reaction arm which is curved to match a typical fork. [There are handed brake plates for trikes and there is a fundamental (and subtle) difference in front and rear brake plates too, but that is of little consequence in reality.]

The cable fittings are already QD; if there is a button on the brake lever this sometimes makes enough slack, but otherwise you just wind the barrel adjuster in a few turns, then everything comes off using fingers, very easily and quickly. It takes about ten seconds to remove or refit the cable from the brake mechanism, and it ought to be the first and last thing you do when removing and refitting a wheel.

The only thing that I find is at all slow and fiddly is refitting the reaction arm to the LH chainstay when dealing with a rear wheel with such a brake. It is easier if the clip on the chainstay is the sort that has two bolts in it; one bolt that fastens the clip to the chainstay, and another separate bolt that secures the reaction arm to the clip itself; this way the reaction arm ought to line up with the clip again quickly and easily.

FWIW some SRAM/Sachs rear brakes used a reaction arm with a pair of heavily built bosses on it; these bosses simply sat above and below the chainstay respectively, so there was less faffing involved. However this cannot work on every bike.

The SA brakes are essentially easy to live with, but there are a few non-obvious aspects of setting them up which can easily trip up the unwary. In particular the height of the reaction arm clip for the front brake makes a big difference to how easy it is to refit the wheel. Also the reaction arms need to be 'set' so that they are not being strained sideways when the wheel is installed; if not then the wheel is less easy to refit and the brakes won't work as consistently well as they should.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

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speedsixdave
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Joined: 19 Apr 2007, 1:48pm
Location: Nottingham, UK

Re: SA front drum brake conversion

Postby speedsixdave » 4 Jan 2020, 10:42am

Brucey wrote:In particular the height of the reaction arm clip for the front brake makes a big difference to how easy it is to refit the wheel. Also the reaction arms need to be 'set' so that they are not being strained sideways when the wheel is installed; if not then the wheel is less easy to refit and the brakes won't work as consistently well as they should.

cheers


Does 'set' mean 'bent', Brucey? And can you expand on the correct height of the reaction arm clip?

I took a punt on an X-FDD for the front of my Moulton (see previous thread on blowouts) but I think getting it to fit is beyond me. So I plan to repurpose the X-FDD on my commuter. Again it's not a completely straightforward fit, will need at least a different reaction arm clip I think.
Big wheels good, small wheels better.
Two saddles best!

Brucey
Posts: 36851
Joined: 4 Jan 2012, 6:25pm

Re: SA front drum brake conversion

Postby Brucey » 4 Jan 2020, 11:35am

speedsixdave wrote:
Brucey wrote:In particular the height of the reaction arm clip for the front brake makes a big difference to how easy it is to refit the wheel. Also the reaction arms need to be 'set' so that they are not being strained sideways when the wheel is installed; if not then the wheel is less easy to refit and the brakes won't work as consistently well as they should.


...Does 'set' mean 'bent', Brucey?....


that's about the size of it

…. And can you expand on the correct height of the reaction arm clip?.....


In the simplest terms it needs to be set as low as it can be. With the wheel in, and the brake arm 'set' to the correct lateral alignment, you should slide the clip down as far as it will go. There is a ~10mm wide 'tang' on the end of the brake arm which is about an inch long. If this always enters the reaction arm clip before you need to worry about the axle going into the dropouts, it makes for easier refitting of the wheel, every time. When the clip is set correctly the top half of the tang will be visible above the clip.

FWIW you can buy reaction arm clips in various different sizes; IIRC the one that comes with a new hub will fit most traditional profile forks with a 1" steerer. You will need a different clip for many other forks, and occasionally something will have to be made/adapted to suit.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~