Differential Shimmed and Jigged

In order to get the differential running smoothly I had to shim and make a simple jig.

Burrell differential

My original differential for the Burrell used bevels with a 20° angle. These kept locking / binding.

Luckily JG pointed out my errors and made a number of calculations to come to 9.5° as the correct angle.

As you can see in the image above, the pinion gears sit through the ring gear and a crown wheel fits either side. One crown wheel has a central phosphor bronze hub that acts as the bearing for the ring gear and the other crown wheel. This phosphor bronze bearing has an axle fixed to it that transfers the drive across the cab to the other drive wheel.

This sandwich of gears meant that I needed some thin shim washers of different thickness to allow me to get the gear engagement correct. So, I made some brass washers from different gauges of brass sheet. I ended up with washers 0.46mm, 0.23mm and 0.12mm thick. Made using a process similar to that for making soft copper washers. I drilled and reamed a 10mm hole through the brass sheets. To ensure they didn’t tear I sandwiched the sheets between two thicker pieces of aluminium sheet. Once drilled I then clamped them onto a shaft and turned the outer diameter.

brass shim washers for the differential

So, I made some brass washers from different gauges of brass sheet. I ended up with washers 0.46mm, 0.23mm and 0.12mm thick. Made using a process similar to that for making soft copper washers. I drilled and reamed a 10mm hole through the brass sheets. To ensure they didn’t tear I sandwiched the sheets between two thicker pieces of aluminium sheet. Once drilled I then clamped them onto a shaft and turned the outer diameter.

With a bolt through the centre of the differential and a block of aluminium to provide the outer face for one of the crown wheels I was now able to operate the differential. A bit of trial and error with the shims and I had something reasonable.

Lots of oil, but even so, at first it was very clunky. After some turning by hand I then put it into the lathe, gently held the ring gear and ran it. A bit aggressive, but now it is much smoother.

You can see that the engagement is not perfect, but as yet I have not made the outer bearing for the crown wheel and the gear that drives the rear wheel. This bearing will make the crown wheel more stable, at the moment it tends to wobble.

The differential shimmed and jigged and operating. I can now move onto the differential axle and the gears that drive

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