Hyundai HD78 PTO – Vacuum-Actuated, Low-Speed Version

In the Hyundai HD78, the PTO functions as a dependable interface between the main transmission and the hydraulic pump. By selecting the correct PTO, you can transfer engine power to dump systems, vacuum units, and industrial hydraulic equipment in a safe and controlled manner, while preventing premature wear and failure of the transmission and pump.

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Vehicles & Gearboxes

2
Compatible Gearbox IDs

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Technical Specifications

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Transmission Interface

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Hydraulic Pump Interface

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Rotation Direction & Speed

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Auxiliary Equipment

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Warnings & Critical Notes

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FAQ

To mount the PTO to the main transmission, a rectangular interface port with six fastener holes is provided on the gearbox housing. These holes serve as the through-points for the mounting bolts, ensuring high structural integrity and rigid fixation of the PTO to the gearbox. This geometry improves assembly repeatability and helps mitigate oil leakage and internal-component damage by maintaining proper sealing and alignment.

This PTO is specifically designed to be installed on the left-hand side of the transmission. The rectangular 6-bolt port is secured using appropriate fasteners and sealing washers to keep the PTO rigidly seated against torsional pulsations and torque transients produced during pump loading. Correct gasket thickness selection is essential for sealing performance and precise face alignment.

PTO gears must mesh with the transmission gear set with high accuracy and correct backlash. In this model, the gears are right-hand helical, relatively coarse-pitch, and housed within the PTO casing. Tooth form, module/pitch, and center distance are engineered to deliver smooth, low-noise, impact-free torque transfer. PTO assemblies may be configured as single-stage (single-gear) or two-stage (two-gear). Single-stage designs are more compact and suitable for light-to-medium duty. Two-stage designs increase torque capacity and load endurance, making them preferable for heavier-duty applications.

In single-gear (single-path) PTO designs, the entire geartrain follows one mesh path and is generally adequate for light to medium hydraulic loads. This configuration is compact and widely used for general-purpose applications with lower torque demand.

In two-gear (dual-path / multi-stage) PTO designs, the geartrain is distributed across two distinct mesh paths, increasing torque transmission capability and load endurance. This type is more commonly utilized in industrial equipment and heavier-duty vehicles, providing improved stability under harsh operating conditions.

PTO engagement systems may be mechanical, pneumatic, vacuum-assisted, or electric. In the Hyundai HD78 PTO discussed here, the actuation method is vacuum-assisted, meaning the operator controls PTO engagement/disengagement through a mechanically commanded system supported by vacuum assistance for smoother engagement. This method is straightforward, reliable, and typically sufficient for most dump-body hydraulic applications.

The output interface of this PTO is configured as UNI, enabling straightforward installation of standardized pumps. This design facilitates proper shaft alignment between the PTO output shaft and the pump input shaft, improving torque-transfer stability and reducing coupling stress.

Depending on pump type, three coupling approaches are used:

1. UNI Pumps: Direct, fast mounting to the PTO UNI output.
2. ISO Pumps: Installation via an intermediate adapter / UNI-to-ISO interface.
3. Flange & Cardan Shaft: A flange is mounted on the PTO output, and power is transmitted via a cardan shaft (driveshaft).

The PTO output rotation direction depends on the internal gear arrangement and number of gear meshes:

1. Single-stage PTOs:
   The output typically rotates opposite to the input; i.e., if the input is clockwise, the output becomes counterclockwise (and vice versa).
2. Two-stage PTOs:
   Due to multi-mesh gearing, various rotation outcomes can be engineered. In the model discussed here, the PTO output rotates clockwise, and it must be matched to the required pump rotation direction.

• Mechanical control cable / lever cable: For engaging/disengaging a mechanically controlled PTO from inside the cab.
• Vacuum assist unit: In some variants, used to support smoother engagement of a mechanically controlled PTO.
• 6-spline to 4-bolt flange: For installing a cardan shaft on the PTO UNI output.

This article presents the most commonly used PTO model for the gearbox typically installed on your vehicle. However, your vehicle may be equipped with a non-standard transmission variant due to customization or trim-level differences. To avoid selection errors, record the gearbox identification number from the gearbox nameplate and consult Raman Shams Industries specialists based on the transmission serial/ID so the correct PTO can be specified.

The dump-body manufacturer or body-builder typically specifies which hydraulic pump and hydraulic valve type must be used in the system. Therefore, if you intend to replace an existing pump with a new one, it is recommended that you have a baseline understanding of dump hydraulic pump selection criteria (displacement, operating speed range, rated pressure, etc.) to choose the correct unit. This article introduces the common configuration for your vehicle; however, it is advisable to consult Raman Shams Industries experts before final purchase.