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Old 08-07-17, 10:37 AM   #1
Geekage
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Dahon Uno with rear drums?

It's an old story: boy buys a Dahon Mu Uno with the intention of putting on freewheel rear wheel and a rear brake. Pictures shows a hole in the seatstay bridge, so he thinks it would be straightforward to install a long reach caliper. Well, the stays are pretty thick, so the bridge is recessed in there a bit. Nothing that can't be solved with a lot of spacers, but that's a kludge.

Reading around on here indicates that the hole is more for mounting a fender, not a brake. Boy is sad.

A couple of other threads have mentioned a drum brake in passing, but not really delved into them.

Well, let's address it: has anyone put a drum rear brake on a Dahon Uno? I figure Mu or Speed Uno, it doesn't really matter that much.

There's the Sturmey-Archer X-RD hub. Specifically model THSXD.RBAS.AA0 fits a 1-speed freewheel and has a 120mm spacing. I figure the 7-speed version could be made to fit by messing with the spacers.

I would hope that the torque arm lines up with the hole for the coaster brake's torque arm.

So, it seems that the wheel will fit into the frame. Hopefully, the torque arm can be attached, even if only with a band clamp. The cable stop is on the torque arm, so the brake cable (and housing) can probably be simply zip tied to the frame.

Any other possible gotchas to mounting a drum brake to the bike? Has anyone actually done this?

Yeah, fine, someone's going to say that the braking power is poor. That's okay, it's only a rear brake anyway. It's a shame that the hub is only available in a 36 hole version.

Has anyone done a coaster brake to drum brake conversion on anything- folding or not- and have any helpful advice or insight?
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Old 08-07-17, 10:56 AM   #2
Rick Imby
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So I have no helpful knowledge of drum brakes. However the bolt hole for fenders will work well if you go to 451 wheels from the 406 which put the rim much closer to the hole---you will not be able to use as wide of tires in this case however.

Dahon builds some bikes with caliper brakes and 451 wheels on the Mu frame.

What is the width of your dropouts?
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Old 08-07-17, 11:24 AM   #3
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I'm not too sure about going 451. I'd have to build up two new wheels if I don't want to mess up the geometry too much- the steering is twitchy enough without adding to the head tube angle. Yeah, I know, it's not that much, but still, symmetry. At least I could use my existing front hub. But I'd need to see about tire availability. Maybe, maybe not.

The reach from the fender hole to the rim is about 79mm, so I could use some long reach BMX calipers (DiaCompe Bulldog or Tektro 984, for instance) without needing to switch rims. I'd just need to make sure to get a nutted style (which I assume all BMX are), and make sure the bolt is long enough to accommodate a spacer.

Still, I'm worried about the strength of the bridge when it wasn't designed for braking.

There's a bit of overlap between this thread and the Brompton drum thread, but I figure I won't hijack it since there are some differences.
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Old 08-07-17, 06:44 PM   #4
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Your long reach BMX brakes will not overstress the frame. The bolt hole is used for all the bikes Dahon makes with the 451 wheels.--- The hole is designed for brakes. However the brake will not work well---they do not have the leverage. I doubt you will be able to get the back wheel to skid unless you unweight the back wheel.-- Long caliper brakes do not work well.

The 451 wheels if you build both of them up will not significantly change your handling---except the wheels will probably be lighter and you will have a little better ground pedal clearance..
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Old 08-07-17, 10:27 PM   #5
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Originally Posted by Rick Imby View Post
Your long reach BMX brakes will not overstress the frame. The bolt hole is used for all the bikes Dahon makes with the 451 wheels.--- The hole is designed for brakes. However the brake will not work well---they do not have the leverage. I doubt you will be able to get the back wheel to skid unless you unweight the back wheel.-- Long caliper brakes do not work well.
You're not going to get any argument from me about long reach brakes not working well- especially single pivot ones. BTDT.

But I do have to disagree that the hole was designed for brakes. I cannot believe that any reasonable manufacturer would try to bolt a brake to an unreinforced aluminum tube. This one measures out to be about 1.8mm thick, so it won't buckle like an aluminum can, but it might not survive a hamfisted user torquing down on a bolt through it. A fender is one thing, but a brake is quite another.

Also, most of the other Mu models have V-brakes, except for the SL. And that one has recessed brake nuts, so whatever tubing they're using is reinforced- not the same setup as the Uno at all.

That said, the 1.8mm thick tubing (17mm diameter) is probably strong enough to take regular braking forces. I found a frame parts supplier that sells 19x1.7mm brake bridge tubing, so they're on the same order of magnitude. I'll either find the curved brake bolt spacers that are made for nutted brakes, or I'll make some out of softer plastic to help protect the bridge. The torque on the bolt holes might cause them to ovalize, eventually causing the caliper to press against the stays, but I'll deal with that when it happens.

And the bonus is that going this route will be cheaper than a drum brake. If I find a 28 hole hub, I can reuse the rim and spokes (though they'll be a couple of mm to short). I'll only be buying a caliper, hub, freewheel, and cable and housing. I've already got a lever.

Yeah, braking power will be nothing like with drums, but as I said before, that's okay for the rear.
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Old 08-07-17, 10:50 PM   #6
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Let me give you a little perspective.

I owned a bicycle shop for over 30 years. (several years the largest shop in the state) and personally I have worked on thousands of bicycles. Most of my mechanic work was done in the days of caliper brakes.

I have a Dahon Mu D10---modified a little--- in my front entryway that I put 40 miles on yesterday. Yes it has v-brakes but it also has the mount for fenders/caliper brakes.

The mount for caliper brakes has always been a simple tube between the seat stays of a bike. look at any road bike as to what the brake is mounted on.--

I guarantee you that any caliper brake you mount to the brake/fender mount on your Dahon Mu frame will not damage the frame if you properly install the caliper brake---unless you crush it by tightening the bolt beyond reason.

You are correct the caliper brake if not mounted with a recessed bolt will have tubing matching washers to match the curve of the tube you are bolting to.

Good luck with your project.
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