ISO 789-2:2018

Overview

ISO 789-2:2018 specifies standardized test procedures to determine the lifting capacity of rear-mounted three-point linkage systems on agricultural tractors. It defines how to measure the maximum vertical force the tractor’s hydraulic lift can exert at the lower hitch points and at a point 610 mm behind the hitch on a coupled frame. The standard is intended for comparative, static testing of tractors (and can also be applied to front-mounted three‑point hitches), not for sizing implements.

Key topics and technical requirements

• Scope of measurement
  • Maximum vertical force at the lower hitch points throughout the full range of movement.
  • Maximum vertical force at a point 610 mm to the rear of the hitch on a frame attached to the linkage.
• Test method
  • Apply a vertical, measurable external load and record lifting force and hydraulic pressure at a minimum of six points (including both extremes) across the lift range.
  • Correct measured forces to a hydraulic pressure equal to 90% of the relief valve pressure; the lowest corrected value is reported as the maximum vertical force for the full range.
• Setup and adjustments
  • Secure the unballasted tractor horizontally so tyres/suspension are not deflected.
  • Adjust linkage according to ISO 730 power range and lower hitch point height; upper link length set so mast is vertical when lower links are horizontal.
  • Throttle lever set fully open during tests.
• Environmental and hydraulic conditions
  • Hydraulic fluid as recommended by manufacturer; temperature at test start 65 °C ± 5 °C (or state measured temperature if not achievable).
  • Ambient temperature 23 °C ± 7 °C; atmospheric pressure should not be less than 96.6 kPa.
• Measurement units and tolerances
  • Force, pressure, distance, rotational speed and other tolerances are specified (e.g., force ±1%, pressure ±2%).
• Reporting
  • Test report must include tractor selection, running‑in, adjustments, measured values, any repairs and deviations.

Applications and who uses it

ISO 789-2 is used by:

• Tractor manufacturers for product development and performance validation.
• Independent test laboratories and certification bodies conducting comparative lifting-capacity tests.
• Agricultural OEMs and implement designers evaluating compatibility and comparative performance.
• Procurement teams and technical specifiers comparing tractor hydraulic lift performance.

Practical benefits include consistent, repeatable comparison of three-point linkage lifting capacity, improved product transparency, and harmonized testing across markets.

Related standards

• ISO 730 - Rear-mounted three‑point linkage categories (used for linkage setup).
• ISO 789-13 - Vocabulary and specimen test report (reporting format).
• ISO 3448 - Viscosity classification (hydraulic fluid identification).

Keywords: ISO 789-2, three-point linkage, lifting capacity, agricultural tractors, test procedures, rear three-point hitch, hydraulic lift, lifting force, tractor testing.