Korean mountain orchards — apple and pear in Gyeongsangbuk-do, citrus and hallabong on Jeju Island, persimmon in South Gyeongsang — share a common characteristic: slope. The terraced, hillside, and valley-wall positions that produce the air drainage, light exposure, and temperature moderation conditions favorable for premium fruit production are also the positions that create serious challenges for tractor-implement operation. Slopes of 15–30% — the typical gradient range across much of Korea’s commercial orchard country — are where the limitations of standard rear three-point hitch implement mounting become genuinely dangerous.

The Kit Drawbar, included as standard with the THOR 2.4 stone crusher, converts the machine from rear-hitch mounting to a front-pull (drawbar) configuration that changes the physics of slope operation in ways that directly improve safety, traction, and working quality. This guide explains exactly what that conversion achieves — the mechanics, the practical conditions that call for it, and how to set it up correctly.

The Physics of Rear-Hitch Implement Mounting on Slopes

To understand what the Kit Drawbar does and why it matters, it is necessary first to understand the problem it solves: the mechanical instability that rear-hitch implement mounting creates on steep slopes.

The Rear-Hitch Lever Effect on Slopes

A tractor is a four-wheeled machine that maintains stability by keeping its center of gravity within the footprint defined by its four wheel contact points. On level ground, a rear-mounted implement’s weight adds to the rear axle load — this increases rear wheel traction (generally beneficial) but also adds a rearward moment (torque) around the rear axle that tends to lift the front wheels. Modern tractors compensate for this with front ballasting, and the geometry keeps the center of gravity within the stability footprint.

On a slope — particularly ascending grade — the geometry changes in a way that compounds this problem. Consider a tractor with a 2,300 Kg stone crusher on its rear three-point hitch, ascending a 25% slope:

The slope angle tilts the entire tractor-machine combination rearward. The weight of the machine, which acts downward from its center of gravity, now has a larger horizontal component relative to the tractor’s rear axle than on level ground. The moment arm of this force — the distance from the machine’s weight center to the rear axle pivot point — effectively increases with slope angle.

The front axle becomes increasingly unloaded. The rear-mounted implement weight, amplified by the slope geometry, transfers load from the front axle to the rear, progressively lifting the front wheels off the ground as slope angle increases. At some slope angle — determined by the machine weight, its position behind the rear axle, the tractor’s wheelbase and weight distribution, and the front ballasting — the front wheels lose ground contact.

Steering becomes impossible. A tractor with front wheels off the ground cannot be steered — the steering system controls the front wheels, which no longer have ground contact to provide directional control. The tractor follows the slope direction and gravity, not the operator’s input.

On a 25% gradient orchard slope with a 2,300 Kg stone crusher on the rear hitch, this loss of front wheel contact can occur at gradients well within the normal Korean mountain orchard operating range. Korean mountain orchard operators experienced exactly this problem before the Kit Drawbar solution — tractors working between orchard rows on slopes above 20% with heavy rear-hitch implements were experiencing front-axle lift, traction loss, and directional control loss. This is the specific problem the Kit Drawbar was designed to solve.

How the Kit Drawbar Changes the Weight Distribution

The Kit Drawbar converts the THOR 2.4 from rear three-point hitch mounting to a front-pull (drawbar) configuration. In this configuration, a drawbar extends from the front of the THOR 2.4’s frame and connects to the tractor’s rear drawbar hook — the fixed attachment point positioned at approximately the rear axle centerline. The stone crusher is now towed in front of (rather than behind and above) the rear axle in the direction of travel.

The Mechanical Change and Its Consequences

In the standard rear three-point hitch configuration, the machine is suspended from the hitch linkage above and behind the rear axle. The machine’s weight creates a moment (torque) around the rear axle that lifts the front axle.

In the Kit Drawbar pull-mode configuration, the machine is connected to the rear drawbar hook at approximately the rear axle centerline. The machine’s weight now acts vertically downward from a point approximately at the rear axle — not behind it. The moment arm of the machine’s weight relative to the rear axle is dramatically reduced. Instead of a large rearward-lifting moment, the machine weight now acts predominantly as a vertical load on the rear axle — pressing the rear tyres into the ground without the front-lifting effect.

The 2,300 Kg machine weight that in rear-hitch configuration was lifting the front axle now, in pull-mode configuration, presses both rear tyres down more firmly while preserving front axle ground contact. The practical outcomes of this weight redistribution on slopes above 20%:

Setting Up the Kit Drawbar — What the Conversion Involves

The Kit Drawbar is included with every THOR 2.4 at no additional cost — it is a standard component, not an optional upgrade. The conversion from standard rear three-point hitch mode to pull-mode is described by Watanabe as taking under 10 minutes and requiring no tools. The conversion involves:

Disconnecting the three-point linkage arms: The lower link arms of the tractor’s three-point hitch are disconnected from the THOR 2.4’s hitch attachment points. The top link (position control) is also disconnected.

Attaching the Kit Drawbar connection: The Kit Drawbar — a structural drawbar frame extending from the front of the THOR 2.4’s main frame — is connected to the tractor’s rear drawbar hook via a pin connection. The stone crusher now hangs behind the tractor, connected at approximately rear-axle height rather than suspended from the upper hitch linkage points.

Ground support adjustment: In pull-mode, the THOR 2.4 rides on its own support skids and the rear wheels of the machine (if equipped), rather than being lifted clear of the ground by the three-point hitch. The machine’s ground contact pressure distributes between these support points — confirming correct ground contact before starting the working pass is part of the pull-mode setup check.

PTO shaft angle check: In pull-mode, the geometry of the PTO drive shaft between tractor and machine changes relative to rear-hitch mode. Confirm that the PTO shaft universal joint angles are within the permitted range (typically ±15° from parallel) in the actual pull-mode operating position before engaging the PTO. Excessive shaft angle causes vibration and accelerated universal joint wear.

Operating in Pull-Mode — Practical Differences

Several operational characteristics change when transitioning from rear-hitch to pull-mode:

Turning radius: In rear-hitch mode, the stone crusher turns with the tractor on a relatively tight radius. In pull-mode, the machine is towed — it follows the tractor path but requires a larger effective turning radius because the machine swings wide on tight turns (like a trailer). Korean mountain orchard operators in pull-mode account for this additional turning envelope at headland turns, leaving adequate clearance from orchard trees and boundary structures.

Reversing: Pull-mode implements cannot be reversed in a straight line — the machine will jackknife toward the tractor if reversed. Korean pull-mode operators plan their working pattern to minimize the need for reversing, typically using wide headland turns to return to the next working pass without reversing. For orchard rows that are too short for a wide turn, a brief return to three-point hitch mode for the turnaround may be necessary.

Depth control: In rear-hitch mode, the tractor’s hydraulic hitch controls the machine’s working depth relative to the ground. In pull-mode, the machine rides on its own ground contact supports — working depth is controlled by the support skid height adjustment rather than the tractor hydraulic position. Correct working depth setting is part of the pull-mode setup procedure.

When to Use Pull-Mode vs Standard Rear-Hitch — Field Decision Guide

The Kit Drawbar is not needed on every application — it is the solution for a specific set of slope conditions where standard rear-hitch operation becomes unsafe or operationally impractical. Use this guide to determine which configuration is appropriate for your specific working conditions:

Korean Orchard and Mountain Farm Conditions That Require Pull-Mode

Apple and Pear Orchards — Gyeongsangbuk-do

The primary apple and pear production zones of Gyeongsangbuk-do — Cheongdo-gun, Yeongcheon-si, Gunwi-gun, and Uiseong-gun — are distributed across the lower slopes and valley walls of the Taebaek and Sobaek mountain ranges. Commercial apple orchards in Cheongdo-gun are typically laid out on slopes of 15–30%, oriented for maximum solar exposure on south or southeast-facing aspects. Row spacing of 3.5–4.5 m accommodates tree canopy development and orchard management equipment access, but leaves limited clearance for stone clearing equipment on the steeper sections.

Orchard operators in this region who adopted the THOR 2.4 for stone clearance and tree-row vegetation management consistently report that slopes above 20% require Kit Drawbar pull-mode for both safety and working quality. Below 20%, rear-hitch mode is manageable with proper front ballasting. Above 20%, pull-mode is required — the front-axle lift that rear-hitch mode produces on steeper sections reduces steering precision in tight rows to an unacceptable level.

Citrus and Hallabong Farms — Jeju Island

Jeju Island’s topography is dominated by the volcanic cone of Mt. Hallasan and the surrounding basalt-derived agricultural plains and lower slopes. Most Jeju citrus farming is concentrated on the gentle-to-moderate slopes of the island’s lower flanks — typically 5–20% gradient — rather than on the steeper upper slopes. For most Jeju citrus operations, rear-hitch stone crusher operation is appropriate with adequate front ballasting on sections below 20%.

However, Jeju’s additional challenge is the basalt rock surface itself. Jeju basalt is significantly harder and more abrasive than Korean mainland granite — sustained stone crushing in Jeju basalt conditions creates greater thermal load on the THOR’s oil-cooled transmission than in softer mainland granite. For Jeju operators running long clearing sessions in July–August (the hot season coinciding with the annual basalt clearance cycle), the THOR’s oil cooling system provides the operational continuity that competing machines without dedicated cooling cannot match in this demanding combination of hard rock and hot ambient temperature.

Mountain Farm Access Roads — Gangwon-do

Farm access road construction and maintenance in Gangwon-do’s highland areas — serving the apple, pear, and highland potato farms of Pyeongchang-gun, Hoengseong-gun, and Inje-gun — is the third major application where Kit Drawbar pull-mode provides genuine operational advantage. Mountain access roads in these areas routinely have gradient sections of 15–25%, with the occasional steeper hairpin section up to 30%.

In pull-mode on mountain road construction, the THOR 2.4 acts as a towed implement — the tractor pulls it up the gradient while the rotor processes the road surface. Because the machine weight is borne by the drawbar connection near the rear axle rather than on the three-point hitch, the tractor can devote its full powered axle traction to forward progress on the slope rather than to supporting rear-hitch implement weight. Korean road contractors working on highland farm track construction report consistently better continuous progress on steep gradient sections in pull-mode compared to rear-hitch mode on the same gradient.

What About the THOR 3.0 on Slopes?

The THOR 3.0 stone crusher includes the same Drawbar Kit system and can be operated in pull-mode on slopes in the same way as the THOR 2.4. However, the THOR 3.0’s 3.0 m working width makes it physically unsuitable for many Korean mountain orchard inter-row applications where the row spacing is 3.5–4.0 m — regardless of the slope configuration. The THOR 3.0’s slope work capability is most relevant for mountain farm road construction and large-scale land clearing on open slope terrain, where the 3.0 m width is not constrained by row spacing. For inter-row orchard and narrow mountain terrace work, the THOR 2.4 is the appropriate model regardless of slope gradient.

For Lighter Stone Loads — The EP-EW-4000 Rock Rake as an Alternative

Not every Korean mountain orchard slope condition requires the full crushing power of the THOR 2.4. On established orchard sites where annual frost-heave produces primarily small surface stones below 30–40 Kg, and where no large embedded boulders are present, the EP-EW-4000 Steinrechen (75 HP minimum, 3.6 m working width, Cat. 2 hitch, 540 RPM PTO) provides an effective and lower-cost stone management solution. The rock rake sweeps surface stones into windrows without crushing them — allowing collection by stone picker or hand labor at windrow locations rather than processing the stone in-place.

The rock rake operates at 75 HP — approximately the same tractor as the farm’s potato furrower and planter — which means it shares the existing farm tractor rather than requiring a 180 HP+ machine. On annual maintenance clearance passes of established orchards where the initial heavy-stone clearance has already been completed by the THOR 2.4, the rock rake is a cost-effective annual maintenance implement. The THOR 2.4 is the tool for the initial heavy clearance; the rock rake is the tool for annual maintenance once the large stones have been processed.

Frequently Asked Questions — Kit Drawbar and Slope Operation

Herausgeber: Cxm