I'd take the topshaft , idler(s) and diff out of the trans and inspect those for burrs and flashes. Run an exacto knife through the recess between the teeth.
If there's one difficult area per turn of both wheels; it would be on the diffgear.
If it's roughly 2 to 3 times per turn of both wheels: check the topshaft and idlers first.
You could also try taking the gears out and reassembling one by one: driving the wheels and spur by hand you'd feel the problem disappear when the guitly element is removed (if it's only one)
|