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Spec Master: Crawler dozers

June 12, 2007 |

In the Magazine

Length with blade in straight position, without ripper(feet, inches) [position 1]
If the blade is further out away from the machine, you gain some visibility but lose operator response. If the blade is placed closer to the machine, you have quicker operator response but lose some visibility. The total length of the machine also becomes a factor when transporting medium dozers.

Track length on ground(feet, inches)
[position 2
The more track on the ground (fore or aft), the less machine pitch and greater stability. Longer tracks give you a more stable platform and are good for light dozing and finish grading. The additional track length, however, also adds more weight and makes the machine slightly less maneuverable.

Height to top of cab(feet, inches)
[position 3]
Also a transportation issue, especially with medium dozers, which tend to move from job to job and need to clear bridges and other overhead obstacles.

Ground clearance(inches)
[position 4]
This comes into play especially in forestry and pioneering work, where working around stumps and uneven ground is an issue. Another application where this becomes a factor is soft underfoot conditions. The more ground clearance you have, the better chance you have of not getting stuck. This needs to be balanced by machine designers, however, with center of gravity.

Track gauge(inches)
[position 5]
Track gauge is measured from the mid-point width of one track to the mid-point width of the other track. A wider gauge typically gives you better machine performance when working on slopes.

Operating weight with dozer blade and
without ripper(pounds)
Make sure you know which dozer blade is being figured into this since blades can vary in weight. The weight and balance of the machine are critical. Typically more weight and horsepower is required when you need to push heavy loads in a mass production situation. Balancing the front of the machine with either a counterweight or ripper comes more into play when finish dozing.

Net horsepower
Horsepower is usually more critical in heavy dozing, when you’re looking for high productivity. With finish dozing, it becomes a factor in steering. A dozer should have a good horsepower-to-weight ratio. If you have too much horsepower and not enough weight, you’ll spin the tracks, lose productivity and waste undercarriage life. When there’s not enough horsepower and too much weight, the machine will struggle to stay up with productivity demands.

Transmission and drive
Transmission type
Power-shift transmissions have generally taken the lead over mechanical transmissions in heavy dozers, although mechanicals are still used. Power shifts offer less operator fatigue since operators shift with buttons instead of levers. Smaller dozers feature hydrostatic transmissions, which give you infinitely variable speeds and greater maneuverability. Hydrostatic transmissions, however, are more susceptible to contamination, keeping them out of heavier dozers. Torque-divider transmissions are more efficient than torque-converter types, but they also take up more space and are more expensive. Both torque-divider and torque-converter transmissions are seen on heavier machines.

Steering system type
Most present-day clutch-brake systems are electric over hydraulic, allowing finger-tip control in large tractors instead of the old lever-pedal controls. Clutch-brake systems allow you to pivot turn by locking up one track and turning on the other track. Differential steer systems are a bit more costly, but you gain the ability to power turn and counter rotate since there’s power to both tracks. Dual-path hydrostatic transmissions are used primarily on smaller machines, and give you the ability to pivot turn, counter rotate and maneuver in tight spaces.

Gear speeds, forward and reverse
If the machine has a power-shift or mechanical transmission, it has three forward and three reverse speeds. Hydrostatic transmissions have infinitely variable speeds. While using third gear for long periods of time is discouraged because it accelerates undercarriage wear, this may be less of a concern in the future as undercarriage designs and materials advance.

Maximum travel speed
Be sure you balance the speed and gear selection in your dozer operations to the undercarriage wear. Because of their infinitely variable speeds, hydrostatic transmissions have more flexibility in this area than power-shift or mechanical transmissions.

Undercarriage
Track shoe widths available (inches)
As a general rule, try to use the narrowest shoe with which you can maintain flotation. Be aware that wider tracks start adding weight and tend to make the machine less maneuverable. Wider tracks are recommended, however, for jobs that have soft underfoot conditions or slope work. Some users run narrow track shoes with wide-gauge tracks, thinking it gives them better stability in finish grade work. Be careful of running wider shoes in rocky conditions since the track pads incur more stress.

Standard track shoe width(inches)
Standard track shoes will suffice for the majority of applications. Each type of undercarriage – extra long, extra wide or low ground pressure – will typically have their own standard shoe size, although all can be customized. The width of the dozer blade can also affect the width of the track desired.

Ground pressure(psi)
This is a factor of the weight of the machine, length of track on the ground and the width of the track pad. Wider tracks and more track on the ground lessens ground pressure.

Blade
Blade type
There are a number of blade options, all designed to address the needs of specific dozer applications. These include U blades, which are shaped to retain the material as you load, allowing you to move large volumes of material. Carry dozer blades add even more volume, but lose some penetration ability and so are better for loose material. Semi-U blades are suited for utility dozing and have a great deal of flexibility in changing ground conditions. Straight blades have limited applications because material retention is less. Power angle tilt, or PAT, blades are flexible and useful in finish grading and a variety of other applications.

Blade width(feet, inches)
This becomes a concern on smaller dozers if you want to be able to move the machine on a truck without taking the blade off. When you get into medium-size dozers, you’ll usually be required to take the blade off the machine in order to transport it.

Blade height(inches)
This dimension is critical for large tractors since you don’t want any material coming over the blade and getting into the radiator or the front of the tractor. Height also becomes a blade weight factor and must be balanced with the weight of the tractor. Blades are typically shorter on smaller dozers because visibility is so important.

Blade capacity(cubic yards)
This will vary depending on the type of blade used, but is usually listed in specification tables as the capacity of the standard blade. Consider the productivity you require on a job when selecting both the tractor size and the type of blade to match with the dozer.

Blade dig depth(inches)
This is a key factor, especially if you are doing a lot of finish grade utility work with smaller tractors.

Maximum blade tilt, hydraulic(inches)
The amount of blade tilt is limited by the track since you don’t want the blade push arms to touch the track. Dual-tilt tractors offer more blade tilt on both sides than does a single-tilt tractor. With a single-tilt tractor, there’s more tilt on one side than the other. Blade tilt is more important on medium-size tractors while blade pitch is generally more important on larger machines.

Ripper
Ripper depth, multi-shank (inches)
For medium-size dozers, a multi-shank ripper with curved teeth is usually used since you’re not trying to pry out large obstacles or rocks. This type of ripper loosens the top material so you can doze it.

Ripper weight with one shank(pounds)
The weight of the ripper many times serves as a counterweight on machines carrying a heavy blade. Parallelogram single-shank rippers are needed for rock or hard conditions. Depending on the application, there are shanks that can go as much as 15 feet deep working behind a large tractor.

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