This is a service and repair manual for BDU-10/21 hydrostatic transmissions.
This manual provides instructions for servicing the Hydro-Gear BDU-10/21 hydrostatic transmission, which is designed for the transfer and control of power with infinitely variable speed ranges. It covers both the BDU-10S model with a self-contained fluid supply and the BDU-10L/21L models with external reservoirs. The document details the unit's axial-piston design, including variable displacement pumps and fixed displacement motors.
| Charge circuit flow | Constant flow across a small fixed orifice |
|---|---|
| Low speed movement capability | 2 mph (3.2 km/hr) |
| Auxiliary pump rated flow | 1.5 gpm (5.67 l/min) |
| Auxiliary pump operating pressure | 500 PSI (34.5 bar) |
| Recommended engine oil viscosity | 20W-50 |
The bypass valve permits moving the vehicle for short distances at low speeds without starting the engine.
Yes, minor repairs may be performed without voiding the unit warranty if the procedures in the manual are followed.
Lip type seals are used on the pump input shaft, pump through shaft, motor output shaft, and displacement control shaft.