Shimano Roller Brake: No User Servicable Parts

If you have to cut through a product with a hacksaw, it’s probably never going back together again.

I was fortunate enough a couple of weeks ago to win an Ebay auction for a Shimano Nexus 7-speed hub gear unit. It was a bit grubby and didn’t come with the shifter, but I did manage to get it with the roller brake unit thrown in.

Ordinarily you can get the Nexus hub without the brake unit and a little bushing-cum-cover for the blank side of the hub, but I have a different idea. I think I can use the brake mount to fit a hub generator to.

I’ll probably go over this in more detail once I acquire the needed dynohub to gut and show some of the reasonably minor mods I’ll be making to the Nexus hub itself (all reversible I expect, so don’t panic). But for now I just need the plate that meshes with the gear hub.

The middle bit with teeth is what I'm after

The other side of the brake was brown from overheating, and the drum’s aluminium heat-sink was pretty warped too, so there wasn’t much guilt in tearing it open. Plus the frame I have is made for rim-brakes (even if it wasn’t, I’d rather not put that extra force on the spokes of using hub-braking).

I clamped it carefully in a vice, after finding there wasn’t enough clearance to simply pry up the three retaining lugs and release the brake drum, and used a hacksaw to cut across the fold of the lug. I cut through enough that it folded back and the drum got a lot freer.

A lucky fluke, the tab stayed attatched but folded aside

That didn’t quite get it loose enough though, so I had to do the same to another tab until it finally popped free.

These things are not meant to be taken apart. They’re sealed units that are only available for replacement whole.

Parts apart

From here it just took a few taps with a leather mallet to knock the steel drum out of the heat-sink. It was just a press-in fitting with some mating teeth.

The prize!

The 4 holes, btw, are for the dust-seal which I’d already removed before cutting began.

Hopefully I’ll attach this to a custom aluminium enclosure I’ll be housing the guts of a Sturmy Archer Dynohub in. It’ll be a lot easier than designing and making my own generator from scratch, and I’m pretty sure it’ll fit once all the heavy steel shell is removed. But anyway..

The mechanism of the roller brake is interesting. It’s similar to a drum brake, but the brake pad is spring-retained. The “nut” in the middle turns when braking is applied, pushing the rollers in a carrier outward as they’re usually against the flats of the nut, but get pushed to the higher corners. This makes the rollers push the brake pad outward in all directions against the brake drum. I thought there might be some braking force applied against the rollers directly, but the brake pad doesn’t move relative to the rollers.

Brake actuator
Roller carrier and rollers

Like the hub gear, these brakes need an anti-rotation/non-turn washer on the axle as that’s what it uses to anchor itself, not to the frame directly.

Unless I’m missing something, calling this a roller brake seems mostly a way of avoiding calling it something as old-fashioned as a drum-brake. But that’s essentially what it is, though with a clever mechanism for increasing brake-pad contact area.

It’s probably about the same contact area as rim-brake pads, only without the benefit of as much mechanical advantage on the wheel.

And yet more..

So after I got my card working again, I got money out and went to put some on the Oyster so I could use the bus.

“Your Oyster balance is negative £2.60. If I put a fiver on it it’ll only be £2.40.”

I tried to tear the damn card in half on the spot, but it’s too thick.

I got it replaced to fix this shit. The last time I used it was going to the Pembury a fortnight ago. I made sure to touch in and touch out at every turn, and it green-lighted me each time. But I still got charged a max-daily for my trouble.

By the by, it turns out my National Rail Card is already applied to the Oyster, so I get a grand total of no additional discount. So if you assume a SINGLE mis-read in a full days use, it’s cheaper to buy a fucking travelcard.

Right, off I went to buy a bus-pass. Oh, no, apparently this is the year they’re no longer doing them. It’d have to go on the Oyster.

Asked at the train station. Travelcard will be £7.30. To get that amount on the Oyster I’d now have to put a tenner on it. Railcard discount’s weekends only, and apparently there’s no off-peak on weekdays now?

Also ran into someone I used to work with and held the train doors for them so they wouldn’t miss it. Good deed +1.

I went home and got my bike.

Up The Avenue there’s road works. I sail through on the manual “GO” sign. As I’m cresting the hill I come face to face with a Landrover and have to ditch onto the pavement.

The driver doesn’t even slow down. I get to the other end of the works and ask the guy if they’re on the radio. I tell him he should leave more time between changing signs since I just got ran off the road. I may have said “fuck” once.

The guy with the radio starts yelling at me not to yell at him and makes gestures like he’s going to get out of the cab and come across to me. I am in shock and back down; he glares like I shouldn’t be taking up his precious world with my existence.

Get half way up Friday hill before I collapse and just have to let my legs stop shaking. A car goes past, and actually reverses back to stop and ask if I’m alright. I explain the situ and assure them I don’t need help.

The lady in the house I’m sat outside calls down to ask if I’m alright. I explain again and have a little rant about the events so far today. She agrees and says the country’s going to pot, and that she was going to be doing a degree this year, but the student cuts mean she probably won’t be able to afford to anymore. There’s a child in the window beside her. I don’t know if it’s hers or a sibling, but it hits home if you were a young-mother or similarly on the borderline of being able to afford extra education, these cuts will have thrown a lot og hope back in your face.

Tried to sugest she should make sure she knows her neighbours. Community’s the only way we’re going to get through this.

She offered me a drink, but I’m very aware the recyc center will close for sales at 2.

Coasted down to the center and had a word with the totters; they said if I spotted something in the hoppers it’d be fine to bring it over to them and ask a price. Finally some good news!

I checked the on-display finds first and picked up a sci-fi art-book for 10p, then hit the metals bin. Pretty full, and quite a tangle.

I spotted a motor with a nice pully and a few bits of thick steel, but they were all too far in, and I lost my damn grappling hook trying to get them out. Fishing for them with a long pole didn’t work either. When I gave up it was 1:40.

Did have another word; they can’t keep and eye out or reserve things. Others have asked too. But they did say they get the sort of bits I’m after in. I’ll just have to keep coming back. Fridays and Saturdays, 10-2, Friday Hill.

Went to walk/cycle back. Ended up “exploring” some back-streets while my mind reeled. Ended up near Chingford Mount, so detoured to the camera shop I’d spotted.

Asked if they had any junk cameras. The guy there was very tidily dressed, and obviously knew his trade. He also kept junk cameras for spares; mostly the odd screw sizes used. After some rumaging and chatter, picked up a broken Fuji F401 FinePix for a fiver.

It may be cheaper to grab junk cameras from ebay in future, but this does looks like it has the lens assembly I want on it.

Home again now, in the workshop (4.4c). Ankle got pushed too hard today. Again feels like there’s glass in it in certain positions. Especially when turned to the side.

Was going to cancel going for a drink tonight in town after finding how much the ticket would be, but fuck it, I need a drink with a friend today.