Not surprisingly, putting this back together is harder than taking it apart!
You should begin with the main spindle shown below :
The thumb spring is hooked on to a little notch, see photo's. With the spring in place you can slide the thumb lever on.
The thumb lever should move between these two stop points.
The thumb lever is hooked onto the other end of the spring you fitted in
the previous step. First hook the spring into the hole in the thumb
lever and then rotate it so that it sticks between the two stop pins
Once the thumb lever is in place, add the thin washer, and then the bushing for the ratchets.
The lower ratchet just fits over the bushing fitted in Step 19. Check
that the pawl is under tension from it's spring, if not and assuming you
didn't remove the spring, keep rotating it clockwise until it is under
The upper ratchet pawl just slide on too in the same way, except that it does not have a bushing.
The ratchet wheel is fitted next and must be put in the position of 1st gear, have a look at the photo for it's position.
The cable wheel is keyed into the ratchet wheel and only fits in one
position. Slide it on to the main axle with it's bushing and keep
rotating it until it slots into the ratchet wheel. You don't actually
need the gear wheel slotted in yet, but it's really helpful to know
where the correct position is later on (when fitting the spring)
With the cable wheel slotted in, you can also add the spring, the spring fits into a slot in the gear wheel.
The spring needs to have a small amount of tension so that it can always
return to 1st gear. This is the hardest part of getting these shifters
First of all, you need to slide the tabbed washer onto the main axle,
with it's tab pointing towards the thumb lever. Then you can slide on
the cross shaped bushing. With those two on tighten the nut on part way
to hold it all together.
Now, pull the gear wheel away from the ratchet wheel (be careful not to
knock the ratchet wheel out of place) and rotate it clockwise until the
free end of the spring locks into the upper (in the photo) slot in the
tabbed washer. Keep a mental note of how much you rotated it.
With the spring locked in place you can rotate the gear wheel counter
clockwise until the gear wheel locks back into the ratchet wheel
(keeping note of how much you turned originally helps here!)
Remove the nut that is holding the gear spring tight - you'll need to
hold onto the tabbed washer to keep the spring from popping out. Replace
the plastic cover. Then replace the part that keeps the top ratchet in
place and tighten the nut back on. Tighten it all the way till it's
tight and then loosen it about half a turn.
Test the gear changing mechanism, it should work now. If it's too tight
or loose adjust the nut. Be careful with the thumb lever as the stop for
this is in the hoods so if you push it too far it'll pop out of place.
If it' doesn't return when you press the thumb lever the gear return
spring is probably not tensioned right.
There is a small hole for the lever return spring to fit into. Put it in place.
Next you can push the brake lever on, then add the bushings. Tighten the
bolt reasonably tight, not really tight!. Then fit the little screw on
the back of the lever.
Fit the brake return spring into it's hole on the lever. Then push the
brake assemble into it's housing at a slight upward angle (from the top
of the housing towards the bottom). This is so that the spring hooks
onto the housing. When it's in place - hold it tight and slide a screw
driver through the axis that the brake pivots on. Test that the lever is
under tension and returns to the normal position, if not you'll need to
remove the brakes and get the spring hooked on properly.
After you've got the spring right, you can slide the brake axle in,
pushing the screwdriver out as you go along. Watch the position of the
groove in the axle, it's offset and needs to be in line with the little
grub screw. Once it's in place, you can tighten the grub screw. Check
the brake still returns ok.
The final step is to re fit the plastic covers, one on the front and the cover on the side. Test it, and enjoy riding!