The 502 diffs are fine if you pay attention to the following :
- DITCH THE KIT DIFF BALLS !!! They are worthless. I still believe it's a disgrace that Tamiya includes such sub-standard parts in such an expensive kit. Tungsten or ceramic balls are available from TRF or other brands. I prefer Tungsten myself.
- Do not use the Tamiya ball diff grease. It hasn't changed since the 90'ies so it is too thin for present day power levells. There are several aftermarked alternatives
-If applying grease to the diff gears, be sure this grease cannot enter the diffs. so use grease very sparsely on the gears or don't use any grease at all.
- be sure to precompress the diff spring before building the diffs
- I believe tamiya suggests in its manual to use anti-wear grease on the thrust bearing. Use a good ceramic or graphite grease instead.
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