Episode 16 – Building a gearbox

Building a vehicle in the size of a tractor, sooner or later you will get confronted with the problem, that you want to be able to drive forward and backward. Knowing that we would face this problem during the planning of this whole endeavour, it was a nice coincidence (or not 😉 ) that Fiat/Iveco relied on Fuller/Eaton gearboxes to cope with the torque of the V8s. Fuller parts and gears are used in a lot of pulling tractors, so having two of these gearboxes should contain enough parts to make our tractor go forward and backward.

Time to have a look into one of these (in)famous Fuller gearboxes.

To much gears, for what we will need, let’s just rip it apart.

First we wanted to use several forward gears, to be able to adjust our wheel speed between runs. But this will just result in extra weight and a further possibility to make a wrong choice for a run. If you don’t have a wrong forward gear, you are not temtded to use it 😉

Not needing that huge housing, we’ve built one out of aluminum plates. Lots of machining to fit the original bearings and tons of drilling and taping.

Since the housing became a lot shorter, the shafts needed shortening and further machining and we needed to find a way to connect the gearbox onto the rear axle.

We were able to reduce the number of gears drastically. Time to explain what will be going on.

  • The input shaft will drive the top left gear at engine speed, which drives permanently the countershaft and the idler gear.
  • The output shaft is driven by the sliding sleeve, which allows to change gears (the gearbox is shown in neutral).
  • The gear on top right turns freely on the output shaft and is permanently driven by the idler gear.

To drive forward, the sliding sleeve is slid to the left and connects the input and output shafts. The output shaft will turn at engine speed.

To reverse, the power will flow through the complete gearbox. The sliding sleev is slid to the right and engages the top right gear onto the output shaft. Through the gears on the countershaft in combination with the idler gear, the output shaft will turn in the opposite direction, compared to the input shaft with a 4:1 ratio.

Moving images are better then a lot of words 😛

Another part of the drivetrain is working, but there are still a lot of parts to be made.

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