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axle supports

Cleaning up the differential.

An auto differential will have several connection points for things like leaf springs, control arm, and other mechanical interfaces but I don’t plan on using them. I will utilize the two large pads near the hub that used to carry the leaf spring mounts, as these are placed at equal distances from each hub, and offer a sold base to weld to. It is also possible to weld directly to the axle tube, as it is just non hardened mild steel.

grinding axle supports

Chopping the control arm mounts.

The control arm mounts are hacked off using the zip disc. I was careful to not dig into the axle tube, as this is a sealed environment that carries oil from the “pumpkin” to the bearings at the hubs.

cleaning up metal

Cleaning up the axle welds.

The flap disc is always used to clean up a rough ground area as well as completed welds. Flap discs are made of overlapping sandpaper flaps, and they do a great job of removing paint, spatter, and leftover rough spots from grinding.

chacking gear ratio

Marking the wheels and differential input.

Most auto differentials have a 1:3.25 to 1:3.5 gear reduction, but the only way to really know is to test it for yourself. To check the gear reduction, you need to mark both wheels as well as the input to the differential, and then give both wheels a full revolution at the same time, keeping the tap on both wheel in alignment. I counted 3.5 revolutions of the input as my wheels made it once around, to as expected, my differential had a 1:3.5 reduction.

What this means is that the input has to revolve 3.5 times for each revolution of the wheels.

removing motorcycle forks

Taking apart the minibike front end.

A motorcycle front steering system is made up of the same parts as a bicycle front end; head tube, fork stem, bearings, and cups. Being a “triple tree” fork, both fork legs are easily removed from the clamping hardware be removing a few cap screws. Bearings and other hardware are collected for later use.

cutting motorcycle head tube

Salvaging the head tube.

A motorcycle head tube can be chopped from the frame just a like a bicycle head tube, the only difference is that there may be other gusseting material and that the tubing will be heavier wall. A zip disc makes easy work of removing the head tube from the rest of the frame.

motorcycle front end

Front end ready for implant.

The entire motorbike front will be used as is in The Yard Mule. Even the front brake can be used as a parking brake, although it won’t really be require do the extreme gear reduction of the completed transmission. Shown here is the removed and cleaned head tube, ready for welding into the new frame.

adding sprocket

Sprocket mounting considerations.

I wanted to keep ground clearance as high as possible, so I chose a socket form my collection that was just large enough to clear the four mounting holes on the differential input. If I needed to go large some day, I still had room to work with, and the lowest point is still the underside of the differential housing itself. I do intend to go into the bush with the Tard Mule, so keeping transmission components off the ground is important.

drilling sprocket

Drilling the Sprocket.

I will go into the details on how to perfectly hand drill a sprocket using just hand tools in the DIY Plan, but here is the result, a sprocket that now mounts to the differential input. This is 32 tooth sprocket designed for a number 40 chain, plenty robust for this application.

sprocket on differential

A converted chain drive differential.

Now my differential can be driven from the side be a chain transmission. This configuration allows the use of both an electric or a gas motor, like the side-shaft snow-blower motor I originally considered using here. In this case, I will have the electric motor drive a jackshaft and then the differential to offer an even greater gear reduction for amazing torque.

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