STEP -BYSTEP Speedo

STEP 1 DRIVE TIME

Cable exits top (early boxes, left) and bottom (late boxes, right). Gear spirals are reversed to maintain clockwise cable drive. The broken anti-clockwise box (bottom) is a hybrid.

STEP 4 WASHING UP

Now the drive gear is free to come out for a wash. Dirt inside is the primary cause of jamming and failure. It’s worth pumping in new grease once a year in order to flush it clear.

STEP 7 CAPS BACK

Once cleaned out, you can press the spindle caps back in while in the vice. Be careful, because the zinc alloy of the box is very weak. Use Loctite if the fit is loose, but it should still grip.

STEP 2 CLEAN-UP OPERATION

It’s worth stripping these boxes to clean them, as they get gritty inside. First carefully prise out the cupped washer and felt dust seal, then remove the steel washer beneath.

STEP 5 END SWAP

Swapping the ends will reverse the rotation. An old cable ferrule protects the threads while I gently tap the box away from the vice, gradually withdrawing the knurled end.

STEP 8 NEW RIVETS

Replace the rivets, supporting the heads on a flat socket while peening over the ends with a flat punch. If necessary, new rivets could be made from joiner’s panel pins.

STEP 3 REMOVE RIVETS

The drive gear is secured by a stepped washer, held by four rivets. Support the box and drift these out from the inside using a sharp punch – they should be re-useable afterwards.

STEP 6 THRUST WASHERS

Watch out for the steel thrust washers on either end of the driven gear spindle as you remove it and tap the blind cap out, using a long punch through the spindle chamber.

STEP 9 REDIRECTED!

Success – a reconditioned and redirected Norvin speedo drive to replace the broken one that came on the bike. Now I can see if the bike is really as fast as it feels!