Tomos A35 clutch repair
This guide will teach you how to re-cork your clutches instead of buying new ones ($75 each) and also how to make them last longer by turning fig 3a into fig 4a
Note: If you have the money, it is worth REPLACING the clutches as the cork wears out at the same rate as the crappy metal the clutches are built from. However, the method of corking here applies to new clutches as well. The style of corking has actually gotten worse from the original transmissions as shown in the picture, and you are better off replacing the cork whether the clutches are old or brand new. Additional methods such as cutting diagonal slots into the cork may even perform better, however the longevity of the design hasn't been tested by me.
Eventually the clutch parts will break apart and grind up all the parts, spitting them into the transmission for further damage to ensue.
The clutches can be readily serviced while the engine / transmission assembly is still installed on the moped. They are located under the cover on the right side of the transmission.
- Drain the transmission fluid.
- Remove the right side pedal crank.
- Check that the pedal shaft is free of burrs so it will not damage the oil seal as you pull it through.
- Remove the seven Allen head bolts around the outside of the cover and carefully pry the cover loose and pull it straight off (it has alignment pins). There may be shim washers on the pedal shaft and the ends of the internal shafts, note carefully their location.
At this point you can see the first gear clutch; inspect it and decide whether you need to proceed further.
To remove the clutches, use a 17mm socket to unscrew the clutch nut (conventional right-hand thread). This nut is on the engine crankshaft, therefore to prevent the shaft from turning remove the spark plug and insert a cylinder lock or a length of rope to jam the piston. Keep track of the lock washer under the nut. Slide the clutch drum and rotors off the shaft. Note there is a shim washer on the crankshaft below the clutch assembly.
The first gear clutch is free at this point; to work on the second gear clutch remove the snap ring with snap ring pliers and slide it off of the drum shaft.
What you will need:
- a square of cork (mine was a package of squares which are used for a small message board)
- a palm sander or equivalent
- Devcon II super glue, or something equally as good
Thinning the Cork
First, the square of cork you are using is probably much much too thick (mine were 4mm thick) they need to be approximately 2mm thick when finished. Go ahead and sand it down a decent bit (to maybe 3mm) (to make it more flexible) and then cut into strips measuring exactly 15mm by 80mm.
Sand off the remaining cork and roughen up the metal on the clutch to ensure the glue sticks well. As accurately as possible, glue the strips from tip to tip following the fig 4a design. After holding till its set, i recommend rolling the clutch with a bit of force to ensure all parts are glued down well.
Sand the overhanging edges and round all corners, sand the “bridge” between the strips in order to make a “ramp” to reduce wear (DOES WORK) as seen in picture below
Fitting the Clutch
Then, attempt to put the clutch back into its housing. It probably won’t fit so carefully sand down each side evenly making sure to maintain the ramp effect at the gaps. Sand until the clutch fits into the housing with just a bit of a gap as shown below.
That's it. Remember where all the parts go, and reassemble with confidence knowing the new design won’t get torn to shit and will last longer. Reassembly is the opposite of disassembly, of course. Be sure to get all the spacers/shims back in their proper places. The long cover bolt goes in the top center hole. Always use new ATF to refill the transmission.