Differential Building

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The parts to build the L4 differential are shown below. It is quite easy to get right as long as a little care is taken. 


The first thing to do is to sand the diff rings on a flat surface with very fine wet and dry as shown below. The diff rings are pressed so are not quite flat. The side you want to sand is the one where the outside sticks out very slightly.

The sanding will give the diff balls more grip on the plates and so make the diff slip less easily.

A 100 tooth Kimbrough spur is supplied with the kit. If running with a 19 turn motor (which is recommended for beginners) it is not always possible to mesh the gears when using the correct pinion for the motor. Kimbrough do several spur sizes. 88, 96 and 100 tooth spurs are shown below, and the 88 tooth is the easiest to use when running a 19 turn motor.

Use 6 diff balls in the spur gear, and fit them in alternate outer holes in the spur as shown in the picture below. 

Then put a tiny amount of diff grease onto each ball. Too much just attracts dirt and does not make the diff work any better. 

The Associated diff uses a flanged bearing for the spur gear. I find that this catches slightly, so I put a single rear axle shim on before the bearing, as shown in the picture below. 

Besides this, build the diff exactly as the instructions show, making sure you put on your newly sanded diff plates with the sanded side facing the spur. 

You will need to put shims on the axle to get the rear track correct, and spaced correctly side to side. You are likely to need more shims than are supplied in the kit, depending on what make of rear wheel is used (more on this later).

It is advisible to slacken off the diff nut between meetings, as the diff puts a lot of pressure on the outer bearing (the one nearest the nut) and doing this can make the bearing last longer.

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