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Originally Posted by starscream

I have experienced the same lurching after a fast run down the straight...
neither of the diffs should have any affect with coasting though so I have found it difficult to identify as well.

The diff's should mostly only affect on power handling. Any lurching would seem to indicate either binding somewhere in the drive line or the esc/motor braking. I used a metal pinion and it was eaten up after just two runs (Metal to Metal). I just picked up some hardened steel pinions today, from Mega Motors, so I'll let you know how the hold up and if the lurching issue is resolved. I am also working on a very simple plastic spur solution so I'll report on that as well.

There's definitely more drag from the front diff than from a 2wd vehicle with no front drive mech. When ever you have drag or braking from the front wheels you will have more weight transfer to the front than a Rwd vehicle. I hoping that by lightening up the diff oils I can reduce drag and get a better off power corning vehicle, but I don't want to loose much of the good on power handling it currently has.

I'm using a hardened steel pinion. It shows very little (if any) wear, and is properly engaged with the spur.

Keep us informed on your plastic spur. I am tempted to try that, but the hardened pinion is so easy and reliable.