hatrack71

Hello, I picked up a Mobiky Genius with the Sturmey Archer SRB3 rear 3 speed hub and brake. There are a couple of questions I have.

On the brake (left) side, I notice little bits and chunks falling out of the recessed area under the black cover plate. They seem to be orangeish or yellow in color and kinda feel like they could be a brake pad surface perhaps. Is there an actual pad or shoe that mounts in that slot? If so, are replacement shoe/ pads available?

Secondly, even after adjusting chain tension, it still won't go into 3rd. I haven't oiled it yet if that is even possible. Anyway.. any help appreciated.. included an exploded view of the hub so I can identify the deteriorating part. thanks

Dan Burkhart 

That is a band brake, the friction material is usually a reddish or yellowish colour, so it sounds to me like the pad is disintegrating. The pad is a strip mounted on the inside of a steel band that contracts around a drum to brake the hub. It is an external unit that screws on to the hub shell, and not part of the hub.
As for not going into third gear, most likely a shift cable adjustment issue. Are you sure the cable ends are securely seated?

fietsbob

I don't think there is a "They" anymore , the new Sun Race TW owned S-A company doesn't make that sort any more..

Maybe Old British retail shops have some in a dusty corner ?

How about a strip of leather shoe sole material ? and replacing it with that , Yourself.

S-A 3 speed broken cable default gear is 3rd . cable too tight?

hatrack71

Thanks. Have you made a repair with sole material before? If so, would you mind explaining how you attached it to the metal band so it doesn't move under braking. Seems like the bond between a rubberish material and a flexy band would be dodgy. But I'm all for trying if you've reported success.

fietsbob

Brass rivets .. through Holes the flat rivet Heads get sunk in deep; enough to not contact the Drum.

Its Victorian era technology . like 1899 era.



I'm just an old mechanic offering some suggestions , you didnt go first to the company and ask them ?
for the search impaired : here > EASYBIKE GROUP https://www.mobiky.com/en/folding-bik...eds-louis.html
Parts would ship out of France .




You could scrap the current hub rebiild the wheel around one of S-A's Drum Brake 3 speed Hubs ..

They got retained in the Product line , I have been using their 6 speed freewheel-drum Hub for 20+ years .

Dan Burkhart 

Replacement bands are available. This is what it looks like.
Bike Bicycle Mini Gas Electric Scooter Band Brake Shoes Jaws Replacement 80 90mm | eBay

Dan Burkhart 

Sturmey Archer still offers a band brake type hub, but only in rotary shift model it appears. Sturmey Archer | RS-RB3
It's a regular right hand English thread on the left side of the hub for the drum to screw on.

hatrack71

Sweet! Thank you. Is it the 80 or 90mm I'm after?

Dan Burkhart 

You will have to measure the drum to find that out.
You can also get complete replacement brake units. I expect yours look a lot like this?
https://www.ebay.com/itm/Band-Brake-F...4AAOSwSHZWcSo2

fietsbob

I tend to think about Making stuff , the forum seems to prefer finding stuff sold on Amazon Or Ebay.

RS-RF3 seems to be the only one not 135 wide ..

the early Da Hons had a band brake too

Dan Burkhart 

Making stuff is commendable, but my time to make a new lining out of an old shoe, assuming I had one laying around, would be worth more than the 8 bucks or so to buy the replacement.
Been quite a while since I've even dealt with a band brake. I think they may still be in use in parts of Asia, but never really caught on here thankfully. Not a big fan of the design myself.

carhillclimb

Hatrack71 -
Do you still have that bike with the SRB3 hub? I want one of those hubs if you are willing to sell it, assuming it is not the wide version for fat-tire bikes.

Yes I know this is a 5 year old thread.

The idea is to thread a trials freewheel on instead of the band brake, and driving a chainring on the left side, simulating a multi-speed fixed. Yes I know I could do this with an S3X, but I already have that setup.

Dan Burkhart 

A band brake uses a right hand thread, A left side chain will unscrew the cog.

carhillclimb

I am not planning to use a fixed cog. I am planning to use a trials freewheel. I have one set up this way already on a double sided fixed/free hub, but the RS-RB3 would allow me to make one with IGH instead of a derailleur for the right side forward drive. A trials freewheel is needed on the left backdrive because otherwise the "lash" is too high. BTDT. I forget if I have a 108 or 120 position freewheel. The most I have seen is 135 but I do not think they were available when I did my bike.

So any hints on a used RS-RB3 or SRB3 hub?

Dan Burkhart 

Oh, ok, I did not realize you were looking for a reverse gear. In that case it would work. I guess I'm not up on this whole trials thing.
I don't know where you could get one. SJS Cycles, who carries just about everything Sturmey Archer shows only the fat bike version and it is out of stock.
Looking at the Sturmey Archer site, it appears that the wide version or the model with a cog bolted to the right flange for tricycle mid drives are the only band brake models currently in production, so used or NOS are your only options.