power shift or direct

I just was wondering what the reasoning is behind Cat making direct drive and powershift. I was reading up on dozers and wondering about my d6c. You see about as many directs as you see powershifts in d4s and I was wondering if each version works better for a specific job. Also, the d4e had a 3304 with only about 75 hp but the 518 skidder had the same engine with 120 hp, what's the difference?



Thanks, Randy

The company were likely responding to buyers preferences by making both types of transmissions available. Any new technology is usually met with some scepticism by the consumers and I'm sure the trans was no different. Of course some were ready to adopt the new thing immediately wondering why it took so long to reach the market.

The direct drive is likely superior to the powershift with torque converter for pulling implements, while the powershift is best for dozer work. Modern ag tractors all have powershift transmissions, but seldom have torque converters unless they are lockup type. The slip of the torque converter is just too inefficient in draft work but its torque multiplication effect is great for dozer work where loads vary so greatly.

The engine is spec-ed to provide the best level of usable horsepower for the machine it is installed in. Can probably quarrel with the engineers a little, but a dozer with 125 hp instead of 75 would likely spend a lot of time spinning the tracks or in the shop for final drive repairs. Put that 125 hp in an ag tractor and it would be an asset. In fact CAT did just that with some tractors I think were called Special Ag models. They generally had a derate on the fuel injection curve when in any of the lower gear ranges. Probably one of the more extreme examples of this principal is the repowers done to CAT tractors for ag work. I think one of the most common was putting a 235-250 horsepower 6V-71 Detroit diesel engine in a D69U tractor that would have had the rack set to about 75 hp as a dozer. These conversions had the lower 1 or 2 gears of the 5 speed transmission blocked out to keep the final drives in them for a reasonable time before overhaul or failure. I think they still required regular maintenance to the finals even without the lower gear(s).

Power shift was introduced in the early 60's and was big productive improvement in applications where speed and direction were changed often such as dozer/ ripper work. The continuous pull under load in farming creates excessive torque heating especially in the earlier models. The 3304 engine was used in many applications and horse power settings depending on fuel setting, RPM setting, and turbo chargers used. For example the 3306 engine in an early D6C was about 125hp and was used in a scraper application at 300hp. I would think the D4E would have more than 75 hp, we pull a 12 offset disc with 26" blades with my 3304 powered D4D S. A. with 20 inch pads in 5th gear with out pulling the engine down but it gets a little light on the front on the tough spots and could use some more weight on the front end.