Česky English


Torpedo is a German brand name for single-speed hubs with a backpedal brake, here in CZ we use it as a nickname for similar hubs of all brands. The design is rather old, but proven, very reliable and still in widespread use. Its main field of application are short-range utility bikes. Main weakness is that the brake is not very strong and can overheat on long descents, up to a point of burning the grease in it. Another little disadvantage is that the bike can't be walked backwards because the brake locks it.

Under normal circumstances, the hub is totally bombproof and can run for years without maintenance. All that needs to be done sometimes is checking/replacing the grease end checking the brake lining for wear. Many different manufacturers produce these hubs, but good news is they all look the same on the inside, so the same procedure and tools should work for any brand.

How does it work

The sprocket is clipped or screwed on a driver that sits on two ball bearings between the axle and the hub shell. The driver contains a one-way friction clutch which engages the hub shell when pedaling forward and spins freely otherwise. At the end of the driver, there is a toothed one-way clutch that spins right cone of the brake mechanism while pedaling forward and presses it into the brake lining when backpedaling (and yet another one-way clutch prevents the cone from spinning backwards in such case). Left end of the brake lining gets pushed onto the left cone, expands and engages against the hub shell. The braking torque is transferred to the left cone via two teeth and from there through a reaction arm to the left chainstay. The left braking cone doubles as a cone for the left ball bearing.

Brake lining is usually made of bronze. It is cracked (intentionally) at one place to allow expansion and a steel clip compresses it back to idle position. Outer surface of the lining is decorated by grease deposit grooves. When these wear down completely, the grease spreads into continuous film and the brake becomes a plain bearing. It's necessary to install a new lining before this happens.

Stripdown and maintenance

Start by unscrewing the left cone. The locking nut is usually round with two notches, this is the spanner designed for it:

torpedo spanner

It's best to have two of them because the square hole fits onto the axle end, preventing it from turning when you work on the nuts. But it's not critical, you can improvise with standard spanner and pliers.

When the left cone is removed, everything else goes out through the right side. There are no traps inside, the parts hold together by C-clips and nuts of standard sizes.

Where to apply grease? It's best to spread it everywhere in a thin layer, including the brake lining. Just don't put too much of it on the friction clutch rollers - if they stick, you're going to freewheel in both directions.