RC diff feels inconsistent? Rebuild it with fresh oil
If drive comes and goes through a corner, the diff is the first suspect: tired oil, a slipping ball diff or a worn part. Rebuild with fresh oil, check the crosspin and outdrives, and set ball diffs just short of slipping.
Why it happens
A diff lets the wheels turn at different speeds through a corner. Its behaviour depends on the oil (gear diffs) or the tension (ball diffs). Both drift over time, so the car feels different from one run to the next.
Check in this order
- Rebuild with fresh oil. Used diff oil thins out long before it looks dirty.
- Oil weights. On cars with front and rear diffs, run the front thicker than the rear for stability on power.
- Worn parts. Check for a cracked crosspin or rounded outdrive cups.
- Ball diff tension. Retighten to just before the point it slips under power.
- Leaks. A weeping gear diff loses oil and changes feel through a session; replace the seals.
Parts that fix it
- Diff oil: Diff oil
- Differentials and diff parts: Differential
- Bearings: Bearing
FAQ
How often should I rebuild an RC diff? Every few months of regular running, or as soon as the car feels different from session to session.
What diff oil should I use? It depends on the car and surface. Start with the kit's recommended weight and change one diff at a time.
How tight should a ball diff be? Just short of slipping under power. Too loose and it slips; too tight and it wears the plates and balls.