Shimano_7_Speed

Shimano 7-speed hub gear

Photos relating to these notes can be viewed here.

Instructions for the removal and refitting of rear wheel in bicycles fitted with this gear mechanism

How the mechanism works

As with all hub gears, the hub contains a system of cogs which allows different ratios of pedal revolutions to wheel revolutions to be selected. The same result is provided more transparently with a derailleur gear system by shifting the chain between different sized chainrings (front) and sprockets (rear).

Selection of the desired ratio is effected by the changing mechanism fitted to the hub. This mechanism is connected by a cable to an operating device which would typically be a thumb-shifter or a twist-grip on the handlebars.

The changing mechanism comprises two main parts:

The cassette joint pulley is the larger part. It has the cable attached. Rotation of this part in discrete steps engages the seven gears in ascending or descending order. Minimum cable tension accompanies the lowest (easiest) gear.
The cassette joint bracket is the smaller part. It appears to nestle inside the cassette joint pulley. It is attached via the cable guide sleeve to the cable casing. It remains stationary with respect to the axle at all times.

N.B.

"Cassette joint pulley" has cable attached.

"Cassette joint bracket" is of a darker metal.

A small locking pin should have been supplied with the changing mechanism. This pin prevents rotation of the two parts relative to one another.

There is also a lock ring which secures the changing mechanism to the hub.

Procedure for removing rear wheel

Select the lowest gear.
Insert locking pin into hole in cassette joint bracket. It may require pressure and/or wiggling to go in fully.
Turn bicycle upside down.
Loosen wheel nuts with 15mm spanner.
Undo them enough topull the round washers and non-turn washers clear of the frame to each side, noting whether the tabs of the non-turn washers are positioned towards the front or towards the back of the drop-out (slot on frame in which axle sits). Wheel should now be loose in drop-outs.
Lay bicycle gently on its left hand side, keeping wheel in position.
Now slide wheel just free from drop-outs.Remove right hand wheel nut, round washer (checking for asymmetry, eg. is it textured on one side?) and non-turn washer.
Press down on lock ring and rotate it anticlockwise approximately 45 degrees to a natural stop. If released, it should now spring upwards and can be removed.
The remainder of the mechanism can now be easily removedfrom the hub.
The wheel can now be pulled clear of frame, for thechanging of a punctured inner tube or any other desired purpose.

Procedure for refitting rear wheel

Place wheel so that it is nearly in place (the bicycle should still be lying on its left hand side) but with the axle clear of the drop-outs.

Align yellow arrow marks on cassette joint bracket with yellow arrow marks on hub. Press changing mechanism firmly onto hub so that it sticks. Gentle pressure on the cable guide sleeve may be helpful.

Align yellow spot on lock ring with yellow spot on cassette joint pulley.

Press lock ring down (towards hub) and rotate it clockwise approximately 45 degrees to lock.

Refit right hand washers and wheel nut loosely.

Slide wheel into drop-outs.

Turn bicycle upside down.

Position wheel correctly in drop-outs (check position of brake blocks with respect to rim) and tighten wheel nuts.

Turn bicycle the right way up.

Remove locking pin to release gear changing mechanism for operation. Keep locking pin safe for next time.

Ariadne Tampion
November 2004