Locking the Differentials;

You can lock all of the diffs if you wanted to but you only need to lock the central one to prevent the power from unloading to the front wheels.

To do this, simply take apart the central diff and turn two of the 4 planetary gears backwards. Turn the two gears on opposite sides of the diff to make sure its stronger.

 

Leading Edge clutch shoes;

If you find that the clutch slips when you try to pull away on a slope, this will help fix the problem.

Clutch shoes can be tuned to improve low end performance by removing material from the shoes. You can also increase the strength of the springs controlling them by getting heavy weight clutch springs available from model shops.

The best way to remove material or lighten your clutch shoes is to drill holes in each of them in excactly the same place. Shown here:

For 1/8th cars, I have found that a 1/8" Drill bit is the best size to use. Start by marking the same place on each of the shoes to be drilled with a pen. Drill the shoes using a hand drill or Dremel tool (do not use a power drill). Because the shoes are now lighter, if they are installed trailing edge (the contact point of the shoe is facing backwards when the engine is rotated counter clockwise) the shoes will slip and not provide the power to the clutch bell. Turning the shoes round, leading edge; shoes facing forwards when the engine is rotated couter clockwise (see picture above); the shoes will "bite" the clutch bell and engage solidly. As the shoes are lighter they will be forced apart by the centrafugal force of the engine at a later stage in the rpm, so will bite later with more power.