Well the ball diff seems to be designed to have that movement. The red (urethane?) sponges and the C caps on the inboard driveshaft end seem to be designed as dampers to keep the ball diff centered in the gearbox while giving some shock damping buy allowing some side to side movement. I guess there is sense to that, but it would certainly help if the diff instructions mentioned that the diff moves inside once the gearbox/chassis is sealed.
I think perhaps I overtightened it as it is now almost a spool. With one hand it will spin like a spool with the TCS 540 stock motor installed, with two hands it still takes a big effort to make them spin opposite directions / diff action.
I may try loosen it at the next race.
I raced the car all day yesterday in TCS. I missed the first 2 quals as i was still building it!! but made the 3rd and ended 3rd. This automatically meant I missed A main which was irritating after being up the night building, but was more relaxed and let me play with the car without pressure. The car is TCS rules set up with most of the Tamiya hops ups (but I forgot to buy the 1050 bearings for the front alu knuckles
). Carpet racing. I did cut away alot of the rear chassis and "no carry handles" installed. The car ran perfectly fine but understeered alot in the fast corners. To cure this I swapped the rear uprights over so that it had 1.5 toe OUT and this made the car very nice to drive. 1st, 2nd, 1st B main was fun but being mid field in A would have been more satisfying! But the car is built now so I can qual properly next month!
BTW, 2 of the M04 drivers (yes, our TCS allows all M chassis still, so top 4 spots are always M04 cars) ran with a sold front set up, swapping the front dampers for 2 rods! Seemed to have little impact on the handling. Those cars still came 3rd and 6th!
Thanks for the replies re the diff, all!