Description

Sauer-sundstrand Series 51 1992 Service Manual

You ever try to guess the charge pressure on a bent-axis variable motor and end up with a loop-flush shuttle valve stuck open and a puddle of hydraulic oil under a $20,000 skid steer? I have. That’s why when you work on a Sauer-sundstrand Series 51 1992 Service Manual, you don’t guess. This 80-page factory document is what the guys in Ames, Iowa wrote for the techs who built these units. It’s not a reprint or a third-party paraphrase. It’s the original OEM specification.

General Description of the Series 51 Variable Displacement Motors

Section 5 of the manual gives you the full architecture. These motors are bent-axis with spherical pistons, designed for closed-circuit systems. Large displacement ratio – 5:1 – means you get high torque at low speed and decent output at top end. The book explains the SAE flange and cartridge configurations, and it tells you which control families mate to which housing. Page 20 has the technical data table: maximum speed, displacement, flow ratings. That table alone will save you a phone call to the distributor.

Does This Manual Cover the Fuel System?

No. This is hydraulic – zero gasoline, diesel, or spark plugs. If you need engine-side procedures, look at the White Outdoor LT-5 – 700 Series Rider Service Manual or the Maruti MB308 Service Manual Procedures and Repair – Section: Section 8A Wiring D if you’re dealing with a different machine. For hydraulic hammers, the HUSKIE Hydraulic Hammers Service Manual pairs well with this one. But for Series 51 motor internals, this is the only manual you need.

Safety Precautions and Gauge Installation

The manual has two separate sections – Safety Precautions (page 21) and Gauge Installation (page 22). Sauer-sundstrand wants you to install gauges in the charge pressure line and high-pressure side before you touch any control. Why? Because if you dead-head a proportional control without seeing the pressure ramp, you can crack the housing. The gauge ports are 1/4″ NPT, and the manual tells you the exact routing. I’ve seen guys skip this step and blow a shaft seal inside ten minutes. Don’t be that guy.

Torque Specs: Plug / Fitting Torques

Last section of the manual – right before the index – is a dedicated page of plug and fitting torques. These are Sauer-sundstrand factory values, not aftermarket approximations. If you’re tightening the charge pressure relief valve cap, you need that number. I torque every fitting on these motors because a leak on a dual-path vehicle means losing steering pressure. The table includes SAE O-ring, JIC, and metric plug values. Write them in your field book.

What Control Types Are Covered?

The manual walks through 17 different control configurations: Hydraulic 2‑Position Type N2, Electrohydraulic Types E1/E2, F1/F2, Electric S1, Proportional HZ/HS/HP/HC, Pressure Compensator PC, and more. Each one gets a functional description, an adjustment procedure, and an exploded view. For example, the Electrohydraulic Proportional Control EP/EQ has a Pressure Control Pilot (PCP) valve diagram. If you’re troubleshooting a slow shift on a compact planetary drive, that section tells you where to put the gauge and what pressure drop to expect.

Why OEM Documentation Matters

Aftermarket manuals skip the pressure compensator override defeat option and the minimum angle servo cover procedure. This Sauer-sundstrand manual gives you the full factory bulletin – including the 1997 copyright update notes. It’s 80 pages of density. No fluff. No reprints. If you need to understand why a manual transmission is designed differently, the Manual Transmission page on Wikipedia explains the mechanical difference. For hydraulics, there’s Manual Transmission info out there, but that’s irrelevant here. Stick with this factory manual and you’ll have the right specs every time.

Does this manual include wiring diagrams?

No. There are no electrical schematics – the Series 51 motors use hydraulic and electrohydraulic controls, not wire harnesses. For wiring diagnostics, you need the vehicle’s service manual.

What is the publication year, and are there later revisions?

1992 is the original release. A 1997 copyright update appears in the front matter but does not change the core torque tables or control adjustment procedures. Later models (Series 51R, 51-1) have separate manuals. This one covers the first-generation bent-axis motors with spherical pistons. It is still the correct reference for units built before 2000.

You know the drill. Stop wasting time with generic PDFs that fudge the 80-page count or leave out the loop flushing shuttle valve option. Get the factory documentation. Access the Factory Manual.