8 x 6 drive 35 ton crane carrier unit

In late 1959 I was Chief Engineer for Crane Carrier Canada, manufacturer of heavy duty truck chassis for crane installations. We had just completed our first 8 x 6 crane carrier chassis designed for mounting of a 35 ton crane, and equipped with tandem rear drive axles and tandem front axles, one of which was driven. We had built many smaller three axle carriers with both front and rear wheel drive so use of transfer cases to split the drive lines was familiar territory.

Prototype in plant test area

We got an order from Timberland Equipment in Woodstock to build them a four wheel drive tractor unit capable of working in a heavy bush environment with maximum manoeuvrability. They planned to add a winch and boom for log removal out of the bush, and the inference was that if successful, there was potential for a considerable volume of future business.

Four wheel steer in use

We were excited and put all our efforts to produce a top level piece of equipment. By mid summer of 1960, we had completed the unit and shipped it to the Woodstock plant of Timberland Equipment. It was equipped with a GM diesel engine, heavy duty transmission and transfer case, and Clarke planetary drive steer axles installed both front and rear. We had long been using the planetary axles on our large crane carriers, with the planetary gear reduction in the hub of the axle reducing the load requirements on the drive line and differential, and felt that it was an ideal application in this unit. The rear axle was rigidly mounted to the frame and the front axle was pivot mounted to provide rough terrain mobility. Power steering was set up so that either the front axle could be steered alone or alternately, both axles could be steered for minimum turning capability.

I was very proud of that unit as it left our plant, and even more so when I visited Timberland’s plant a few weeks later to see them testing the finished log skidder before shipping it to their customer. The oscillating front axle and four wheel steer capability gave the required manoeuvrability as they ran it over the rough grounds behind their plant.


Showing front axle oscillation capability

However, our expectations of volume business was quickly dashed as the company, sensibly so, after completing the prototype, decided that now they had the basic design they could produce the complete unit themselves. In service, they quickly realised that in the harsh environment in which these machines worked, driving over rocks and tree stumps, the oscillating front axle design, and the vulnerable elements of the steering linkages on the axles had to be eliminated.

Prototype showing transfer case below frame

A change was made to rigidly mount two non-steering axles to the frame, and the frame was separated into two halves, connected at the centre by heavy duty pivots. This design also provided more protection to the transfer case and drive line. Steering was accomplished using hydraulic cylinders to pivot the front and rear sections of the machine horizontally.

Early production skidder with centre frame joint

Over the next forty years they built thousands of skidders which rolled out of the constantly enlarging plant of their newly established subsidiary, Timberjack Machines,