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Tomos A35 clutch repair

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Contents


Introduction

Situation: Your Tomos A35 transmission sounds crappy and the clutch is slipping. Upon inspection it appears your cork has gone through a blender.

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.

Image:tomosclutches.jpg


The picture below demonstrates how the A35 clutch hub can be fit with shoes from A3 clutches with yellow 25lb springs installed. Slight modifications must be made to the A35 clutch hub so the A3 clutch shoes will fit. The hubs are held together and the slots on the A3 hub are traced onto the newer A35 hubs; an angle grinder works well for this. The clutches are then assembled the same way but this time the springs will be visible when the 1st gear clutch assembly is placed into the bell (they face inward with the original shoes).

both 1st and 2nd gear shoes from the A3 can be put on the A35 1st gear hub this way.

Image:Tomosclutcha3-a35.jpg

Disassembly

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.

To disassemble:

  1. Drain the transmission fluid.
  2. Remove the right side pedal crank.
  3. Check that the pedal shaft is free of burrs so it will not damage the oil seal as you pull it through.
  4. 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 deep well socket to unscrew the clutch nut (conventional right-hand thread). This nut is on the engine crankshaft, therefore to prevent the shaft from turning, use a holder tool, or a strap wrench, or 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 behind 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.

Materials Needed

What you will need:

  • a square of cork (mine was a package of squares which are used for a small message board) I highly recommend you look for higher quality cork as there is an abundance at various automotive stores.
  • Another unconfirmed option: Rubberized cork gasket at 3/32 thickness, sold at most NAPA's (this would in theory eliminate the need for sanding to reduce the thickness of the cork), chrome leather, or other friction material.
    • Note: I've tried chrome leather and metallic friction style materials and have incurred issues with longevity and adhesion that i did not experience with the cork. Others have claimed some amount of success.
  • a palm sander or equivalent
  • Devcon II super glue, or something equally as good
    • Note: Gorilla glue has also been used successfully for this application
  • A clutch-sized hose clamp or an oil filter wrench (strap type) works well to hold the cork against the clutch as the glue dries. Just glue one piece at a time and be careful not to glue the cork to the wrench.

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

Image:clutch ramp.jpg

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.

Image:clutch in housing.jpg

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.

Image:clutch.jpg


Also check out this thread for a Helpful Tip for lining up the clutch cover.

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