Gearbox Assembly: Replacing Stepper Gears

Disassembly Using a small, thin flat-bladed screwdriver, gently separate the top and bottom of the gearbox casing. (First try inserting the screwdriver into each end of the casing and gently levering. Alternatively try the tiny slots above each lug). Be patient and gentle: careful not to damage the casing, the plastic is fragile. Two large metal gears (2 & 3) will be retained and three smaller plastic gears (A, B & C) replaced. Ensure the gears are clean, including their center holes.   Replacing the original plastic gears with the precision metal set A, B & C are the new replacement gears, but be careful as A & B are very similar. A = equal smallest diameter gear with thinner outer gear (replacing original red plastic). B = equal smallest diameter gear with thicker outer gear (replacing original blue plastic). C = larger diameter gear (replacing original opaque plastic). 1 = motor pinion, 2 = 2nd last output gear, 3 = final output gear (there should be no need to replace these).

ReassemblyI IMPORTANT: Test assemble the gears one at a time, and all together, before completing assembly. Before installation in the car, the stepper gearbox must be rotating freely with little resistance. Each new gear should spin freely on its bearing pin although it is a close fit. If there is difficulty, check the pin for damage or run a #39 (0.099 of an inch or 2.52 mm approx.) hardened steel drill through the gear's centre until it rotates freely on the pin. Now assemble A, B, C and 2 and check they all mesh and rotate freely. Note gear orientation in the diagram.