Broken Coaster Hub

[Jezston]

Seems the rough streets of London have got to me and after just two days of commuting in the city something has gone rather wrong with my 3-speed coaster brake hub geared bike

Something felt a bit 'wrong' riding in this morning, then noticed in first gear the gearing was slipping and jumping a bit. Chain had gone a bit slack and thought it probably just needed the wheel pulled back a bit and the barrel adjuster for the gears tweaked a bit. Then I tried to stop with the coaster brake, and the pedals did not stop turning backwards and just gurgled a bit. Oh dear.

In 2nd and 3rd it rides fine, but pushing back on the pedals to engage the coaster brake just stops the pedals with a clunk, but no braking is felt. I appear to, depending on the rotation of the pedals, be able to push it back a bit further than it should go.

Anyone know what might be going on, what I might be able to do myself before taking it into a shop, or if it indeed sounds repairable at all?

 

[tyred]

I have never worked on a coaster brake with hub gears but the single speed variety are all basically the same. You have a splined shaft attached to the sprocket, there is a wedge shaped device which slides on the splines, when you pedal forward, this slides up the splines and engages the hub shell and drives the bike forward. When you back pedal, it slides out the other way into the brake shoe which expands and provides a brake against the hub shell. I would imagine yours is no different but not sure how the gears fit into it. I'm reasonably certain that Sheldon Brown has a guide to overhauling the older AWC hub which should give you a good idea of what you find inside.

 

[tyred]

This is what you find inside a Sachs Torpedo. The part on the left is the brake expander unit and when you pedal forwards, it moves along a spline to engage the drive on the dog teeth you can see on the back of the sprocket on the right. When you back pedal, it moves to the right and forces the brake pads apart (there is a split, although it can't be seen in that photo) and brakes up against the hub shell which acts as a brake drum. I can't imagine the basic operation of the Sturmey is really that different.

http://www.flickr.com/photos/29091369@N07/6044597587/

 

[Jezston]

Cheers for the info, however I fear this is a bit too technical and I'm too inexperienced to glean anything from it that I might be able to take action on

Time to find a decent repair place that does Sturmey Archer stuff.

Anyone know of such a place in west central london? Or if not in greater London as a whole?

 

[GilesM]

Good bit of info from Sheldon Brown

http://sheldonbrown.com/sturmey-archer/s3c.html

Got to be worth ago, the drawing even shows you where everything goes.