Well, the overhaul to the transmission worked for a while but then after a years occasional use the same old symptoms started to show - sticking in forward and sometimes reverse as well. I had a couple of other things to fix on the mower so I got back into the transmission and had a look.
I had taken a shortcut in the previous overhaul to try to keep the original cork linings, and had rubbed them with metho to get the grease out of them. Turns out that process wasn't thorough enough - the corks ended up with grease on their surfaces again which I assume came from the heat of some hard work mobilised the remaining soaked-in grease, which then transferred to the matching clutch pulley surfaces. The extra slip made me push harder on the clutch pedal to get motion and that higher force contributed to jamming the clutch plate (inner disk with cork) up against its mating clutch pulley (outer disk with the belt). See pic of contaminated surfaces attached.
Since last fix I'd managed to get some replacement corks so I was able to strip off the old corks, clean everything thoroughly and put the new corks on. The old corks mostly just flaked off using a broad scraper and I used paint thinner to get rid of the remaining bits of old glue. One of the pics below shows a cross section of the old cork - the majority of the cork still appears to be OK, so possibly just sanding off the top surface of the old cork might have been OK if I didn't have replacement corks on hand. Interestingly, the old cork pads were thicker than the new ones (3.2 mm for the old vs 3 mm for the new) but that might just have been down to remnants of the glue lining on the old corks.
I was surprised to find that remnant grease in the yoke bar bearing had managed to get back onto the square shaft and gum up the carbon film lube surface there. So, the grease was cleaned away again and the sliding surfaces refreshed, rubbing carbon powder onto the square shaft and the matching square holes of the clutch plates.
With the new corks in place the feel of the clutches is better, with more progressive engagement and no sticking.
Another problem with the original fix was that I'd reassembled the transmission with lots of clearance (extra shims between washers and clutch pulley plates) to ensure that it worked without drag. This had the undesirable effect of both putting the clutch pedal neutral position too far back (hard to press for reverse) and with an unnecessary amount of play. Solution here was to leave out most of the shims and leave just one on the forward clutch (battery side). Even though the clutch pulleys do rub slightly on the clutch plates (the path of the drive belt actually pulls them off line slightly), the pedal play is now OK and it has a better neutral position.
After all of the palava of the original transmission overhaul, this removal, fix and reinstallation took less than a day. The mechanical work went quickly - most of the time was spent waiting for the cork glue to dry.
Other simplifications to the process this time were that the sprocket and shaft bearings came off easily and I managed to find the removable link to the drive chain so that its removal and reinstallation was much simpler.
