Description

Sauer Danfoss Series 20 1984 Service Manual

If you’ve ever wasted a Saturday because some aftermarket manual told you the charge pressure was 50 psi when it’s actually 150, you’ll appreciate what’s in this binder. I’m Mike Callahan, ASE Master since ’96, and I’ve rebuilt more Series 20 pumps than I’ve had cups of coffee. This 1984 OEM manual is the one you want on the bench, not some photocopied reprint with blurry diagrams.

Start Up Procedure – Preconditions for Trouble-Free Operation

Page 6 of this manual lays out the preconditions. You don’t skip those. You check the inlet filter, you verify the oil level, you purge the air. This isn’t a suggestion box. If you fire up a Series 20 without following the first-time operation checklist on page 6, you’re asking for cavitation damage. The manual gives you the exact steps, including the required tool list for startup.

System Maintenance: Oil Changes and Leak Tests

The system maintenance section covers recommended oils – don’t guess. Use the spec listed. The leak test procedure is something I see skipped constantly. You pressurize the system to the specified value and check every fitting. If you don’t have that number, you’re gambling. This manual has it. Also, the cleanliness warnings are not optional. Dirt kills these units faster than anything.

Troubleshooting – What This Manual Covers

Over the years, I’ve seen guys throw parts at a pump because they guessed wrong. The troubleshooting section walks you through symptoms and causes systematically. Low charge pressure? Check the charge check valves. No drive? Check the shuttle valve. It’s all there. You don’t need to guess. Follow the flowchart logic.

Inspection Instructions – Check Charge Pressure

Page 13 tells you exactly how to check charge pressure. You need a pressure gauge rated for at least 500 psi. The spec is in the manual. Don’t trust a generic number. I’ve seen aftermarket manuals that list the wrong relief valve setting. This is the real factory data. You also get procedures for checking charge pump and high pressure relief valve – all with OEM torque values.

Disassembly and Assembly of Variable Displacement Pump

Starting in the disassembly section, the manual gives you a sectional view and step-by-step disassembly. The torque specs for the control valve bolts are critical. Over-torque and you strip the housing. Under-torque and you get leaks. The manual lists them. Use a calibrated torque wrench. Also note that many parts are interchangeable across the Series 20 family – servo valves, charge pumps, manifold components. That’s in the introduction.

A word about aftermarket documentation. I don’t trust it. I’ve seen third-party manuals that claim to cover Series 20 but omit the charge pressure check or use different bolt torque patterns. This is the original 1984 Sauer Danfoss manual. 46 pages, printed in Germany. If you need proof, look at the copyright on the title page. That’s what you want on the bench when a customer’s machine is down.

For other models, consider the Sauer Danfoss Series 90 1998 Service Manual – 88 Pages or the Sauer Danfoss PVG32 2010 Service Manual – OEM Factory Specs. The Sauer Danfoss 45 2005 Service Manual – Factory Specs for Series 45 is also a solid reference for those units.

If you need background on hydraulic theory, Manual Transmission basics are useful, but for these pumps, the factory manual is your only source for accurate rebuild specs. Another external resource is Manual Transmission – though not directly related, understanding power flow helps.

FAQ

Does this manual cover fixed displacement motors?

Yes, it covers plumbing installation for variable displacement pump and fixed displacement motor. The system circuit description is included.

What torque specifications are provided?

Torque values are given for charge pump bolts, high pressure relief valve, servo valve, and other critical fasteners. The manual does not list every bolt in the unit, but for the major assemblies you get factory spec torques in lb-ft or Nm. You must use them – aftermarket numbers often lead to leaks or failures. I’ve seen it happen. The charge pressure check on page 13 also includes the required pressure setting. If you skip that, you’ll never get the pump to perform correctly. I’ve watched technicians chase their tails for hours because they used a generic spec from a parts catalog. This manual eliminates that guesswork.

Is this manual suitable for a beginner?

Not really. It’s written for technicians familiar with hydraulic systems.

Why is the 1984 manual still relevant?

Because Sauer Danfoss didn’t change the core Series 20 design for decades. The procedures, specs, and part numbers in this 46-page manual still apply to many units in the field today.

Don’t trust your reputation or your equipment to a knockoff. Access the Factory Manual and keep it within arm’s reach of your service cart.