With the inching pedal

Caterpillar engineers call the inching pedal by another name. To them, it’s the “transmission modulator control.” But whatever you call it, its function is clear: Depressing the pedal disengages power to the grader’s wheels.

When you put your 120, 140, 150 or 160 Motor Grader with a direct drive transmission in gear, the direct coupling from engine to transmission acts like a clutch on a car or truck. So if you want to slow the machine, you’ll push the inching pedal in or shift back into neutral.

The more you push down on the inching pedal, the greater the decrease in power to the wheel. And inching lets you vary machine ground speed while keeping engine speed high — for quick implement response.

Note that the inching pedal should not be used for shifting gears while the machine is moving. Doing so may shorten transmission clutch life and accelerate damage to the drive train.

Without the inching pedal

On the other hand, GC Series motor graders use a torque converter, where fluid is spun from one side of the engine to the other. With your GC, you apply the brake to obtain the speed you want.

If, for example, you’re set up at 2,000 RPM going 26 mph (42 kmh) up that grade, the engine will stay at 2,000 RPM even as the ground speed starts to drop off. This is because the torque converter sends more transmission fluid to the side of the engine with more load on it, causing it to spin slower. In this way, power is always automatically applied by the torque converter where it is needed most.

Because of this, GC motor graders are docile, easy-to-handle machines: When you apply the brake, your ground speed will drop smoothly and predictably. No shifting of the transmission is required. Similarly, when you're going up a grade, the machine doesn't pull down on you.

Because it has a torque converter mechanism, it is almost impossible to stall the engine of a GC motor grader. GC graders give you excellent control over horsepower and torque, so Caterpillar recommends using them in fine/finish grading and road maintenance applications.

If you are, for instance, working in a cul-de-sac at 1 mph (1.6 kph), you'll find a GC motor grader is easier to operate. If you had an inching pedal, you’d have to apply and release the inching pedal constantly as you move around the cul-de-sac to get the fine control and finish you’re looking for. It’d be a lot more tiring on your machine and your body.

Great grader control

Caterpillar engineers have designed all motor graders to be as simple and precise to operate as possible, even with the different powertrain configurations. Both the inching pedal (other than GC) and torque converter (GC) power systems are easy to learn and deliver smooth, precision power on demand. 

Whether you have an inching pedal or not, you can get the control you need — simply being aware of how your motor grader functions is the first step. Understanding the differences between the two systems is critical for operators looking to get the most performance possible out of each.

Want more info about motor grader best practices? Check out these motor grader operating tips.