Rear hub motor disc brake dilemma

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praskal
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Last seen: 11 years 3 weeks ago
Joined: Tuesday, June 5, 2007 - 19:41
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Rear hub motor disc brake dilemma

So I finally got a full suspension MTB off craigslist (like this: http://www.velosklad.ru/i/models/sredn/132.jpg). The only problem is that it has dual disc brakes. I have a rear wheel X5 Phoenix hub motor. Because of this, I can't use the rear disk brake. And apparently I can't install V-brakes because you can't drill into aluminum (or whatever it is). I can't figure out how to put the disc on the left side of the X5 motor.

What suggestions do you guys have?? Should I just bag it and get a non-disc brake bike? Should I keep this bike and only use the front disc for braking??

spinningmagnets
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Last seen: 11 years 7 months ago
Joined: Wednesday, December 12, 2007 - 20:48
Points: 295
Re: Rear hub motor disc brake dilemma

It is correct that if you drill into the thin tubing to mount a V-brake, stress-cracks will form when riding, and it is only a short matter of time before it fails completely.

I strongly recommend making a steel "U-shaped" adapter plate that lays across the top of the rear suspension arm with clamping from underneath. That, plus some JB-weld epoxy and the adapter + V-brake will stay put. You can even start riding with only the front brake, as the fronts always perform 75% of the braking (keeping top speeds moderate at first, of course)

Don't throw away the rear disc wheel. It can be used for a "Peltzer conversion" (want to sell it? what state are you in?) When attaching a large-diameter sprocket to a rear disc, the disc must be epoxied on the threads and pinned radially to prevent it from unscrewing, as the load will be coming from the opposite direction compared to using it as a brake.

praskal
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Last seen: 11 years 3 weeks ago
Joined: Tuesday, June 5, 2007 - 19:41
Points: 34
Re: Rear hub motor disc brake dilemma

"making a steel "U-shaped" adapter plate that lays across the top of the rear suspension arm"

This is a great idea. I guess I could go to my local metal machine shop and see if they could hook me up with such a beast. Basically lay it over the rear suspension arm, clamp it from below with some epoxy, and then drill the v-brake into this adapter? This is possible. Thanks.

Patrick

spinningmagnets
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Last seen: 11 years 7 months ago
Joined: Wednesday, December 12, 2007 - 20:48
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Re: Rear hub motor disc brake dilemma

If you used 3/8" thick aluminum plate, that would be strong enough, and you could easily cut it to shape yourself.

I would attach it with 2 small U-bolts from underneath using thread-locker goop and chrome acorn nuts. The JB-weld epoxy is to keep it from sliding around.

If you wanted to get "upscale-looking" use two aluminum billet clamps like this:

http://www.racecraft.com/prodimages/rack%20clamp.jpg

Do you already have plans for the rear disc wheel? (Google Peltzer electric bicycle!)

spinningmagnets
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Last seen: 11 years 7 months ago
Joined: Wednesday, December 12, 2007 - 20:48
Points: 295
Re: Rear hub motor disc brake dilemma

The front V-brake mount on an MTB is already in the upside-down "U" shape, and already includes the threaded holes in the right spots.

It would be easy to cut it off and adapt it to the rear suspension arm. I have an old MTB that I fished out of the trash to pull a couple parts. I am about to throw it away, if you want it PM me at:

velmis1450bc(at)aol(dot)com

Put visforvoltage in the message line or I'll spam-trash it.

Or, buy one for $10 at a thrift store (the 24" are cheaper, but the brakes are the same as the 26" bikes)

If this would work for you, it would end up looking like this adapter plate:

http://www.bentechbikes.com/p000565.jpg

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