Saturday, August 13, 2011

To sleep, perchance to dream: ay, there's the hub

Hub brakes are like cinema projectionists. You know they're there, but don't know what they look like and don't give them much thought as long as they do what they're supposed to do. Above is the inside of one of my no-name hub brakes on my Christiania front-loading trike. That white stuff is anthrax spores. I held my breath and brushed it off.

Working on the Christiania is not like working on normal bikes. You don't need any hex keys. But you do need pipe wrenches.

Above are the two main parts of the hub.

And on the picture above here you can see Islay, on loan from a friend. I need a dog, at least intermittently. Islay is a quiet, careful dog, and an Iditarod veteran.

That part on the right hand side of the brake that looks like a cylinder is actually sort of flattish. When the brake lever is held in, the wire pulls an arm on the outside of the hub, which in turn makes that flattish cylinder turn, which then forces the two semi-circular arms outwards.

video

As you can see, there's not much play here. Problem is, I don't know how much there should be. I oiled the moving parts, which is a big drama as you do not want oil on the brake pads. I changed the cable and cable housing too. But the brake still doesn't work very well. Maybe opening it up again and giving it a good whack with a hammer will help.

12 comments:

coventry recycled cycles said...

Hey, I've never really had much to do with drum brakes, i had one on a tandem but it never stopped working so i never considered how to fix it!

Now that the brake it all back together again and attached to the lever does it feel like the brake lever is engaging enough? Do bike hub pads usually have grooves in them to aid with stopping/ grip? Is there a wear indicator like on car drum brakes? On normal brake pads I rough them up with a file but not sure you can do this with drum pads- especially if they are asbestos based like their car equivilent

good luck! Jo

Oldfool said...

hmm...I take it there is no brake adjustment screw. There must be some way to adjust for shoe wear.
Perhaps the drum itself is glazed.

Oldfool said...

Hmm...I can't believe there is no adjustment screw to compensate for shoe wear.
Perhaps the drum itself is glazed. I remove the glazing on car drums with fine sandpaper.

Northmark said...

Coventry, Oldfool,
I'm guessing you're both right. Those brake pads (they seem impossible to remove) sure are very, very smooth.

Northmark said...

Boy, bicycle drum brake maintenance, this is arcane stuff. Hardly any information out there. Here's a depressing tidbit: Several drum and hub brake designs utilize internal pads similar to automotive drum brake pads. These pads typically last the life of the component, and severe wear often necessitates total replacement.

But if I listened to that song every time I heard it, my life would be less interesting. More pleasant, perhaps. But less interesting.

Oldfool said...

In automobiles the shoe (it's called a shoe, pads are the replaceable parts on disk brakes) braking surface material is bonded or riveted to the metal part which is the max limit. When the rivets start touching the drum then it ruins the drum surface. The entire shoe is traded in when new ones are needed. How I know this is a lifetime story.
It looks like you have a lifetime left on those, yours and your daughters lifetime. They appear hardly worn.
The shoe material is usually very smooth and hard. The glazing is on the metal drum and you general can't see it. It occurs because of extreme heat which is unlikely in this case. It happens on rotors in disc brakes as well. Like I said I use a little fine sandpaper on the metal drum but if I forget I really can't tell the difference.
Are these brakes stock? Are they part of the original design? Are the levers giving you enough power at the shoe itself? There are levers that will give you more power at the drum. I mixed and matched some on one of my stretched bikes about put myself over the handlebars.
To adjust drum brakes tighten until engaged then back off until the wheel turns free.
Coaster brakes are a drum brake of sorts,they are smooth and hard but because of the leverage give an amazing amount of stopping power limited by the tires friction on the road surface.

Northmark said...

The brakes came with the rig. I don't know the brand, and those secretive Danes won't tell me. But as you say, there's lots of braking material.

I did use this contraption with several dogs hooked up to it (often three, rarely four, as I can recall) before I got a designated rig for that kind of thing. I did do what seemed as really serious braking, but the speed and brake length were not completely out of this world.

I am unhappy about the levers, (no barrel adjusters, and they meet the handle bar too soon) and the cable routing is probably not optimal, too many tight corners. The choice of levers is limited because the handlebars are shaped as an upside-down "U" with tight bends, ruling out the options for flat handle bars. I am seriously considering welding an additional handle bar (sort of like this guy did, as the current one is a bit too low. The brake arm, however, is activated. But even when I activate it manually the wheels just slow down a bit.

I will follow your advice extremely closely.

coventry recycled cycles said...

Looks like we're all going to learn something about drum brakes! sheldonbrown has quite alot to say about these brakes but unfortunately not much about why they might go wrong. I'm with 'oldfool' on checking the inside of the drum...and then giving it a little sand- can't hurt.
On my current tandem i had a bit of a problem with braking- i wasn't confident that when flying down a hill with my daughter in the back that the bike would stop when i wanted it to (Not sure if that was to do with the extra long cables).
I swapped the levers for old school leechi levers and its much better now, must be something to do with the amount of pull you can get on the lever.

let us know how you get on! Jo

Oldfool said...

The dogs would do it. Speed doesn't count in this case but I suspect it was enough to scare me. Prolonged braking would build up the heat plenty fast. They power and speed of dogs just amaze me.

We used to carry charts to consult in the airliners that would tell us how many hours we had to sit after a hard stop.

The Danes are good at some things but I'm not impressed with the design in this case. I'd put some real handlebars.

These brakes are the same design as are on my 1951 bus, they are the same design that was on the big trucks I drove in the '90's and are the same as the rear brakes on three other old vehicles I own. They are the same as my 1936 Ford from many years ago. All actuated differently, e.g.cable, hydraulic, air,but the same brake just the same.

You should be able to retrofit some barrel adjusters. BMX levers are shorter and the ones I have dealt with pull a lot of cable before they hit the handle bars but you need a strong hand.

You resourcefulness does not end when you become a parent so you will figure it out.

william forrestall said...

Hi
Great site you have here , I have over the years enjoyed you posts on the cycle-car projects.

The brake drums for front wheel steering cycle projects look quite useful - are they still made ? do you know the name of the manufacturer ?


We have built a couple ( 3) of cycle- cars mostly out of found materials here is one ( or two) on you tube

http://www.youtube.com/watch?v=JxJLN6A67SU

Here is another with a talk about the building process at the end.

http://www.youtube.com/watch?v=9xfkPvdvAWM

Understand you are a new father now - congrats - best thing that ever happened to me .

All the Best

William

Northmark said...

William,
Beautiful cycle-cars!
I don't know the brand of my hubs, there's no writing on them and the people at Christiania Bikes are pretty secretive, they haven't even updated their web page in twelve years. (Also, they use disc brakes now.)

Sturmey Archer makes two types of hubs w/ brakes for one-sided attachment, a 70 mmm and a 90 mm. Ordering is sort of tricky. There's an interesting post on improving hub brake performance here.

A tip: after opening up the hub, make sure the brake arm is fully activated while closing it all together again.

Anonymous said...

Hi! I stumbled across your blog while looking for info and parts for my old christiania trike. Hope this info doesn't come to late.
I found this site http://acelo-shop.com/ where you can find the parts you need. Going by the pic of the hub, I have just purchased and mounted the same brake shoes http://www.acelo-shop.com/bremsen_trommelbr_00_1691_306_000.html#ENGLISH
The difference is like night and day. Especially because I had four identical shoes when they should be asymmetrical.
Now I have brakes that work 100% I can report that the 70mm drums will at best give you a stopping distance of at least a couple of meters when loaded.
When you talk about brake levers, the handlebars on my trike can be split like a tent pole. The join is under the right hand side hand grip. Not sure if the same solution is used on all there bikes.
Hope this helps
/Kenny