Sturmey Archer drum brakes

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tyred

Squire
Location
Ireland
Anyone have any experience of these (the vintage type)?

I'm working on a 1940s Elswick at the moment and I have confused myself about how the front drum brake should fit into the fork. The back wheel has the drum and brake arm on the left hand side (as you sit on the bike). I know this is correct because the threads for the freewheel are obviously on the other side.

When I got the bike, the front hub was installed with the brake drum and arm on the right. I thought this a little odd at the time as I would have expected front and back to be the same. When I was building it up earlier in the week, I was going to change the front to match the back. I then noticed that the curve on the arm matches the curve of the fork if the wheel is installed with the arm on the right, so I put it in on the right as it was originally. I still can't convince myself this is actually correct, partly because I would have expected it to be on the same side back and front, partly because the cleaned and serviced back brake works brilliantly and the cleaned and serviced front brake is pathetic. I then notice that the front brake works well if you push the bike backwards and apply the front brake, just not when going forward.

I'm tempted to swap it round but then the reaction arm will be curved in the opposite direction to the curve in the fork, which will look odd and I don't understand why it would have been made like that. The reaction arm goes onto the fork with a bolt on clamp, not a braze on, so it is easy to swap it to the other side.

Anyone have any thoughts? Here is a picture of the brake as it is installed at the moment. Note how the curve of the reaction arm matches the curve of the fork blade.
 
Reaction arm on back to front.
 
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tyred

tyred

Squire
Location
Ireland
I don't think you could fit the reaction arm back to front. Not without a great deal of trouble at least.
 

RecordAceFromNew

Swinging Member
Location
West London
I then notice that the front brake works well if you push the bike backwards and apply the front brake, just not when going forward.

IMHO, this is the curious bit, I can't see why this one should be any different but of drum brakes I have played with, when the brake shoes are pushed against the rotating drums, frictional resistance wouldn't be materially different whichever direction it spins.

Can the brake shoes be turned around 180 degrees?
 
IMHO, this is the curious bit, I can't see why this one should be any different but of drum brakes I have played with, when the brake shoes are pushed against the rotating drums, frictional resistance wouldn't be materially different whichever direction it spins.

Can the brake shoes be turned around 180 degrees?

Depends if the shoes are 'trailing' or 'leading'. Depending on the particular arrangement you can have one of each or both 'leading.' Both 'leading' provided optimum braking but is why some old cars' handbrakes worked perfectly well until parked facing up a hill.
 
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tyred

tyred

Squire
Location
Ireland
Take it off the axle, remove and reinstall the threaded cable stop and actuation arm. Reassemble. How difficult can it be?









:reading:

Not difficult at all actually. I was over-thinking it.

It is the only explanation that I can see for it being the way it is.
 
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tyred

tyred

Squire
Location
Ireland
I can't change the reaction arm around. It's riveted to the back plate and clearly designed not to come off so I don't think somebody in the past built it wrong.

I've rode the thing for a five miles or so and I think the brakes seem to have "bedded in" a little and work not so bad now when going forward. I might just leave it for now but I'm still convinced something isn't right. I'll take it on a VCC ride later in the year and let some experts have a look.
 

Ivan Ardon

Well-Known Member
Note: I've never worked on Sturmey Archer drum brakes, but....

Does the brake hub have any free play around the axle? I've worked on drums where you have to tighten the wheel spindle with the brakes applied hard to allow the shoes to centralise within the drum. Otherwise, it'll be off centre, and more as likely only be applying one shoe to the drum, which doesn't help stopping power. Also check that the leading shoe isn't more worn than the trailing shoe.

Your symptoms of the brake being more powerful going backwards points to the (normally) trailing shoe hitting the drum first and stopping the leading shoe from meeting the drum.

That wouldn't apply if the shoes were fully floating, but like I sad, I haven't worked on SA drum brakes.
 
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