John Deere 644K wheel loader: the numbers quarry crews quote back to us

We do not stock quarry-class iron every week—but when a 644K shows up in conversation, buyers want hard anchors. Published literature for the Deere 644K class (K-series frame) commonly cites an operating weight on the order of ~41,000+ lb depending on configuration, with net engine power around ~232 hp class for diesel variants and bucket capacities in the roughly 4.0–4.25 cu. yd. range depending on spill guard and teeth. Breakout and transmission gearing matter as much as peak horsepower for pit load cycles.

The 644K sits in what Deere calls the "medium wheel loader" class—bigger than a 544K but smaller than a 744K. For quarry and aggregate operations, this is the sweet spot: big enough to load highway trucks in three to four passes with a standard rock bucket, small enough to maneuver in a typical crushing plant or batch plant layout without needing a CDL-class haul road. It is the machine we get the most questions about from aggregate operators in the southeast, and it is one we are always looking to source for our inventory at https://equipmentsupplyservice.com.

Spec deep dive: the numbers quarry operators actually care about

Let me walk through the specs that matter for quarry work, and why:

Breakout force:The 644K's static tipping load and Z-bar linkage produce a breakout force in the 37,000–40,000 lb range (varies by source and configuration). This is the force available to penetrate the pile face and fill the bucket. In a quarry loading crushed stone or shot rock, breakout force determines whether you can load the bucket in one insertion or need multiple bites. More bites means longer cycle times, which means fewer loads per shift.

Bucket capacity and fill factor: The 4.0–4.25 cu. yd. bucket is sized for density. Crushed stone at approximately 2,700– 2,800 lb/yd³ puts a full bucket at roughly 10,800–12,000 lb. That is within the machine's rated operating capacity but close enough that heaped loads in heavy material can exceed it. The fill factor—how full the bucket actually gets versus its rated struck or heaped capacity—depends on material angle of repose and operator technique. A good operator in well-broken aggregate achieves 95–110% fill factor; the same operator in large shot rock might achieve only 80–85%.

Transmission and cycle time:The K-series uses Deere's ZF-based powershift transmission with lock-up torque converter. In a typical quarry load-and-carry cycle (pile face to truck, load, return), the transmission's shift quality and torque converter efficiency directly affect cycle time. A well-tuned 644K in a tight quarry layout can cycle 4.5 to 5.5 loads per minute into a waiting truck. That is approximately 650–750 tons per hour with a four-pass truck loading pattern, which is competitive with machines one class size larger in less optimal layouts.

What to inspect on a used 644K

Quarry machines live hard. They eat high-abrasion material all day, they cycle fast, and they rarely get the gentle treatment that a municipal snow-loader receives. When we evaluate a used 644K for potential purchase or consignment, here is what gets the closest attention:

Axles and differentials: The 644K runs heavy axles with limited-slip differentials. We check for leaks at the axle seals, oil condition in both the front and rear differentials, and any play in the output bearings. A differential rebuild on a machine this size runs $8,000 to $15,000 depending on damage extent.

Bucket and cutting edge:The bucket's cutting edge wear rate in a quarry is measured in weeks, not months. We check cutting edge thickness, sidebar wear, and whether the bucket floor has been patched or plated. A new rock bucket for a 644K runs $6,000 to $12,000 depending on configuration. Cutting edges and segments are $1,500 to $3,000 per set.

Tires: A set of four L5 loader tires for a 644K runs $12,000 to $20,000 depending on brand and ply rating. Quarry tires wear faster than any other application. We photograph and measure tread depth on every tire and report it in the listing at https://equipmentsupplyservice.com.

Fuel consumption and operating cost

In a typical quarry load-and-carry cycle, the 644K burns approximately 5 to 7 gallons per hour depending on load factor and cycle intensity. At $3.50/gal diesel, that is $17.50 to $24.50 per hour in fuel alone. Over a 2,000-hour annual operating schedule, fuel cost runs $35,000 to $49,000. Add oil, filters, tires, and undercarriage maintenance, and the total operating cost (excluding operator labor) runs roughly $45 to $65 per operating hour. These are the numbers your cost-per-ton calculation needs to include.

The 644K's 91-gallon fuel tank is a competitive advantage in quarry work. It provides roughly 13 to 18 hours of run time between fills, which means most operations can fill once per day instead of disrupting shifts for mid-day fueling. The Cat 950K's 80-gallon tank provides slightly less buffer, which can matter on extended double shifts.

How we use this in practice

We do not quote someone else's brochure as gospel for a specific serial. We match the machine's build plate, verify bucket pin and coupler class, and reconcile tire size because flotation and tractive effort change cycle times in sugar sand versus hardpack limestone.

When a 644K crosses our intake desk—whether from a consignment, a trade-in, or an auction buy—we run it through the same IRON+ inspection process as any other machine: full mechanical inspection, fluid samples, tire measurements, and a documented test cycle. For quarry-class machines, we add axle oil sampling and a transmission response test because those are the high-dollar failure points that determine whether the machine is a good buy or a money pit.

If you are in the market for a 644K or a comparable machine (Cat 950K, Volvo L120, Komatsu WA380), check https://equipmentsupplyservice.com for current availability. We do not always have quarry-class loaders in stock, but when we do, they move quickly. If you want to be notified when one lands, call us and we will add you to our interest list.