Sauer-Danfoss Series 42 Pump Rebuild Guide: Seal Kits, 1998 Changes, Torque, Neutral and Start-Up

To rebuild a Sauer-Danfoss Series 42 pump, find the frame size (28, 32, 41 or 51 cc) and whether it was built before or after the 1998 block point change, then service the outside of the pump (shaft seal, SCR valves, charge relief, charge pump, control, servo covers and loop flushing) using the overhaul seal kit for that frame: 4510066 for the 28 cc and 4510141 for the 41 and 51 cc. Torque everything to the Danfoss chart, set mechanical neutral and then control neutral, and confirm charge pressure above case: the standard setting is 14 bar (203 psi) on 28 and 32 cc pumps and 20 bar (290 psi) on 41 and 51 cc pumps.

The factory line is clear. Danfoss service manual 520L0638 covers installation, maintenance and minor repair. Removing the rear cover or front flange is a major repair, and Danfoss says it voids the warranty unless a Danfoss global service partner does it. The rotating group procedure lives in a separate Series 42 repair manual, 11007277, which we do not have on file, so this page does not give a rotating group teardown or wear limits. What it does give you is everything the factory publishes for the outside of the pump, which is where most Series 42 seal jobs happen.

What this page is based on. Danfoss Series 42 axial piston closed circuit pumps service manual 520L0638 (Rev 0300, July 2015); Series 42 technical information 11022637 (Rev CG, June 2013); parts manuals 11032042 (28/32 cc) and 11032043 (41/51 cc), including the service bulletins printed in them; and shaft seal kit instruction BLN-10198 (September 2013).

Which Series 42 pump do you have?

The nameplate carries the model number, model code and serial number. On the pre-1998 tag the serial reads like A 97 23 67890: the letter is the plant (A is Ames, Iowa; Y or J is Osaka, Japan), then the year, the week and the sequence number. That date matters because Danfoss says parts may or may not interchange between pre-1998 and post-1998 pumps, and many, including the housing, are unique to the model year change. Our Sundstrand and Sauer-Danfoss identification guide covers reading the tag.

Frame	Displacement	Rated / maximum system pressure	Rated speed at max displacement	Standard charge relief	Overhaul seal kit
28	28 cm³/rev (1.71 in³)	385 / 415 bar (5584 / 6019 psi)	3400 rpm	14 bar (203 psi)	4510066
32	31.8 cm³/rev (1.94 in³)	385 / 415 bar (5584 / 6019 psi)	3000 rpm	14 bar (203 psi)	See note below
41	41 cm³/rev (2.50 in³)	385 / 415 bar (5584 / 6019 psi)	3200 rpm	20 bar (290 psi)	4510141
51	51 cm³/rev (3.11 in³)	350 / 385 bar (5076 / 5584 psi)	2900 rpm	20 bar (290 psi)	4510141

Specifications from 520L0638 page 22; charge relief settings from 11022637 page 9 (optional settings run 10-24 bar, 145-348 psi, on all frames); seal kits from parts manuals 11032042 page 150 and 11032043 page 144. The 28/32 cc parts manual covers both frames but names its overhaul kit only as "28cc," so confirm a 32 cc pump by serial number before you order. Both kits are listed in our store for quote; send the model code and serial and we reply with price, availability and lead time.

What changed at the 1998 block point?

This is the single biggest trap on a Series 42. Danfoss rolled several changes into one model year upgrade (SB-1997-029C), and many of the parts do not mix:

Charge relief: changed from a shim adjustable valve to an externally adjustable one. The adjustable valve needs the 1998 upgrade housing.
Charge pump: the gerotor drive pin became a parallel key, a retaining ring was added to locate the gerotor coupling, and the outer step on the gerotor cover was dropped. The coupling and gerotor set must stay together; a service kit exists for pre-1998 charge pumps (SB-1997-029).
Housing: the servo cover screw holes, four of the six side cover holes and the filter adapter holes are 10 mm (0.39 in) deeper. The longer screws only fit post-1998 housings.
Loop flushing: post-1998 pumps share one loop flushing spool across the 28 and 41/51 cc frames. Pre-1998 spools are unique and do not interchange.
Control spool port (28 cc full-featured housing): a two-screw cover plate became an SAE O-ring plug.

Does the pump need a rebuild, or an adjustment?

Symptom	What Danfoss has you check first
Will not drive either way	Oil level, control input signal, filters, both bypass valves fully closed, charge pressure in neutral and in stroke, servo pressure difference, charge pump damage or wrong rotation, SCR valves, displacement limiters.
Drives one direction only	Control input, SCR valves, a biased control, a blocked servo supply or drain path, displacement limiters.
Running hot	Oil level, heat exchanger, a partly open bypass or SCR valve, clogged filters, machine load.
Sluggish	Oil level, control signal, control spool wear, bypass and SCR valves, charge pressure in neutral and in stroke.
Neutral hard to find	Control input, then pump (mechanical) neutral and control neutral. On EDC units, a pressure difference across the control spool with no signal means replace the EDC.

Low charge in stroke but good charge in neutral points at internal leakage somewhere in the loop, which is a parts question, not a seal kit. The case drain flow test helps separate a worn pump from a worn motor, and our hydrostatic transmission troubleshooting guide covers the whole loop.

Where do the gauges go on a Series 42?

Port	Pressure measured	Gauge	Fitting, 28/32 cc / 41/51 cc
M1, M2	System pressure, ports A and B	600 bar (8700 psi)	9/16-18 / 9/16-18
M3	Charge pressure	60 bar (870 psi)	3/4-16 (some older pumps 9/16-18)
M4, M5	Servo pressure	60 bar (870 psi)	9/16-18 / 9/16-18
L1, L2	Case pressure	35 bar (510 psi)	1-1/16-12 / 1-5/16-12
S	Charge pump inlet	1 bar (30 in Hg vacuum)	1-1/16-12 / 1-5/16-12

Source: 520L0638 page 23. Use snubbers and calibrate gauges often. On pumps with a filtration adapter, the M3 port moves with the filtration option.

How do you replace a Series 42 shaft seal?

Pull the pump and stand it shaft up. If the shaft comes out with the pump lying flat, the cylinder block can shift and the shaft becomes hard to refit.
Remove the case drain plug to break any vacuum.
Pry the end of the spiral retaining ring free and unwind it from the groove.
Pry the seal carrier out on its raised surface, and remove the O-ring. The O-ring may still be sitting on top of the front bearing.
Press the old lip seal out, inspect the carrier, and press the new seal in from the bearing side until it bottoms, pressing only on its outside diameter.
If the shaft comes out, check the splines and the rear bearing contact surface. Spalling means a new shaft and rear bearing, and Danfoss classes rear bearing replacement as a major repair.
To change the front bearing, note the chamfer, press the bearing off, and press the new one on with the chamfer toward the pump, pressing only on the inner race.
Seat a lubricated new O-ring on the bearing, cover the shaft end with an assembly sleeve, lubricate the seal, press the carrier home against the O-ring, and wind the spiral ring back into its groove.

Refit the case drain plug at 120 N·m (89 lbf·ft) on 28/32 cc pumps or 200 N·m (150 lbf·ft) on 41/51 cc pumps. The lip seal for this job is Danfoss 9008000-0131, item C018 in both overhaul kits.

How do you service the valves, charge pump and control?

SCR valves (check, high pressure relief and bypass)

Remove the valve seat plugs with a 1 in wrench or a 5/16 in internal hex, pull the check/relief assemblies and inspect the valves and seats. Danfoss says the SCR valves are not serviceable: replace a bad one complete. Fit a new outer O-ring, backup ring and inner O-ring on each plug, make sure the conical springs are retained and the valve moves freely in its bore, and torque the plugs to 70 N·m (52 lbf·ft).

Charge relief valve

Pre-1998, shim adjustable: each 1.25 mm (0.050 in) shim changes the setting about 4 bar (58 psi). The plug takes 54-136 N·m (40-100 lbf·ft) per the procedure; the manual's torque table lists 90 N·m (66 lbf·ft).
Post-1998, externally adjustable: mark the plug, lock nut and housing before you remove it. About 1.4 bar (20 psi) change per quarter turn. Lock nut 24 N·m (18 lbf·ft) on 28/32 cc, 40 N·m (30 lbf·ft) on 41/51 cc.

Either way, confirm the setting at M3: charge pressure levels off when it reaches the relief setting.

Charge pump and auxiliary pad

Check gerotor tip clearance: seat the set in the cover, engage one inner tip fully in an outer valley, and feel the opposite tip with a feeler gauge. Danfoss allows 0.127 mm (0.005 in) or less. The gerotor is a machined matched pair.
If the drive coupling has worn through its journal bearing into the aluminum cover, replace the cover and coupling. If it is only loose, press a new journal bearing in from the cavity side to 12.88 mm (0.507 in) deep.
Replace the charge pump seal (G023) every time. SB-1998-079 replaced the inner and outer O-rings with a single H-seal from serial A-99-06.
Charge pump cover bolts 45 N·m (33 lbf·ft) in pattern. Auxiliary pump screws 42 N·m (31 lbf·ft) on an SAE A pad, 100 N·m (74 lbf·ft) on an SAE B pad.

Control module, servo covers and loop flushing

Control gasket: on MDC, EDC and HC-EDC pumps the control gasket is also the control orifice, so match the gasket to the order code in the parts manual. The summing link pin must engage the cam slot (MDC) or slider block hole (EDC/HC-EDC). Danfoss says an MDC must align to the housing within 0.005 in or neutral may be off center or impossible to set. Control bolts 17 N·m (13 lbf·ft) in the factory pattern; control spool bore plugs 70 N·m (52 lbf·ft).
Servo covers: bolts 17 N·m (13 lbf·ft) in pattern. Removing the right side cover means you must reset pump neutral and control neutral afterward, and it can move the displacement limiters.
Loop flushing: plug 37 N·m (27 lbf·ft), relief plug 27 N·m (20 lbf·ft). Do not change the relief shims on pre-1998 pumps unless Danfoss tells you to. The relief plug with two grooves is for pumps with charge set at 18 bar (260 psi) or higher; one groove is for lower settings.
Speed sensor: turn it in by hand until it touches the speed ring, back it out 1/2 turn for the nominal 0.71 mm (0.028 in) gap, square the flats at 22 degrees to the shaft centerline, and lock the nut at 13 N·m (10 lbf·ft).

Which Series 42 service bulletins matter on a rebuild?

Bulletin	Applies to	What it changes
SB-1996-021	28 and 41 cc pumps, 51 cc tandems	Ball guide hold-down pins changed from flat to chamfered ends (4700016 to 700091). Danfoss says update older units at first repair.
SB-1997-026	28 and 41 cc	New neutral adjust screw, 96 mm long instead of 93 mm, to take a higher seal nut torque. Do not fit the old screw in its place.
SB-1997-027	28 and 41 cc	New red loop flushing relief spring eliminates shimming. Do not use the old spring in place of the new one.
SB-1998-006	41 cc	Swashplate 4410102 replaced by 4410228 to clear the servo, for pumps built before A-98-05.
SB-1998-079	All Series 42 pumps and overhaul kits	H-seal replaces the two charge pump cover O-rings from A-99-06.
SB-1999-022, SB-1999-044A, SB-1999-064	28 cc and 41 cc (servo and side cover gaskets also on integrated tandems)	New material servo cover, side cover and charge pump cover gaskets that hold torque better. The new charge pump cover gasket needs the ductile iron cover.
SB-1999-037	28 and 41 cc with bypass	Bypass valve 4800600 replaced by 4800768 with a Viton O-ring.

How do you set neutral on a Series 42 pump?

Zero output needs two neutrals: mechanical neutral (swashplate at zero angle with no control signal) and control neutral. Set mechanical neutral first.

Disable the machine: wheels off the ground or the function disconnected.
Connect an SAE-06 hose between servo ports M4 and M5 to equalize the servo, and put gauges on M1 and M2.
Run at normal speed. Loosen the neutral seal lock nut on the right side servo cover, turn the screw until one system gauge rises, mark it, turn back until the other rises, mark it, and set the screw halfway.
Hold the screw and torque the lock nut: 20-26 N·m (15-19 lbf·ft) on 28/32 cc pumps with MDC, EDC or HC-EDC; 40 N·m (30 lbf·ft) on all 41/51 cc pumps and 28/32 cc pumps with NFP controls.
Remove the hose, then set control neutral: disconnect the control linkage or signal, gauge M4 and M5, and split the difference with the control neutral screw the same way. Lock the nut at 40 N·m (30 lbf·ft).

Displacement limiters are set on a flow test stand. One turn changes displacement about 3.6 cm³ (28 cc), 4.1 cm³ (32 cc), 5.0 cm³ (41 cc) or 6.2 cm³ (51 cc), and the seal lock nut goes back at 23 N·m (17 lbf·ft) after every adjustment with full thread engagement.

How do you start up a rebuilt Series 42 and check charge pressure?

Align the pump shaft with the prime mover shaft. Misalignment damages the shaft, bearings or seal.
Fill the reservoir through a 10 micron absolute filter. Never reuse fluid.
Fill the pump housing with clean oil through the uppermost case drain port, and run the case drain line from that port.
Fill the inlet line and check it for tight fittings, restrictions and air leaks.
Put a gauge on M2. Jog the prime mover or run it at the lowest speed until system pressure builds to normal levels, at least 11 bar (160 psi), then bring it to full speed. If it will not hold pressure, shut down and find out why.
Run at least 15 minutes under light load, check and adjust control settings, then shut down, remove the gauge and top up the reservoir.

Charge pressure is a differential: read M3 with the pump in neutral and subtract case pressure. Danfoss rates the nominal settings at 1800 rpm with 28 mm²/s (130 SUS) oil, and says charge drops slightly in stroke. Pumps with no integral charge pump are set with an assumed 19 l/min (5 US gal/min) of outside charge flow.

Limit	Value	Source
Case pressure, rated / cold start maximum	3.4 bar (50 psi) / 10.5 bar (150 psi)	Service manual 520L0638, 2015
Case pressure, rated / cold start maximum (earlier figure)	3 bar (44 psi) / 5 bar (73 psi)	Technical information 11022637, 2013
Inlet pressure, rated / cold start minimum	0.8 bar absolute (6 in Hg vacuum) / 0.2 bar absolute (24 in Hg vacuum)	520L0638
Fluid and filter change, no machine maker interval	2000 hours sealed reservoir, 500 hours breather reservoir	520L0638

Bypass valves are not tow valves. On a Series 42 the bypass is a plunger in each check/relief valve plug, and both must be pushed in. They stay open until the engine restarts or pressure builds. Danfoss limits movement to 20% of top speed for no more than three minutes, and warns that the valves can close if pressure builds, damaging the pump, motor or engine.

More on the fluid side in our fluid cleanliness and flushing guide and pump start-up procedure.

Should you rebuild a Series 42 yourself?

A shaft seal, SCR valves, the charge relief, a charge pump or a control gasket are reasonable bench jobs if you respect the 1998 split and set both neutrals afterward. If the pump was contaminated, Danfoss's own instruction is full disassembly, cleaning and inspection with the repair manual. Metal in the filter, contamination, or charge that falls off in stroke is the point to have it torn down and quoted instead of buying seals.

Frequently asked questions

Is there a Sauer-Danfoss Series 42 service manual?

Yes. Danfoss service manual 520L0638 covers installation, troubleshooting, adjustments and minor repair with a torque table. Major repair, which means removing the rear cover or front flange, is covered by the separate Series 42 repair manual 11007277.

What seal kit does a Series 42 pump take?

Danfoss lists overhaul seal kit 4510066 for the 28 cc pump and 4510141 for the 41 and 51 cc pumps. The 28/32 cc parts manual names its kit only as 28 cc, so confirm a 32 cc pump by serial number.

What should charge pressure be on a Series 42 pump?

The standard charge relief setting is 14 bar (203 psi) on 28 and 32 cc pumps and 20 bar (290 psi) on 41 and 51 cc pumps, with optional settings from 10 to 24 bar. It is measured in neutral at 1800 rpm and referenced to case pressure.

Can you replace a Series 42 shaft seal without taking the pump apart?

Yes. Stand the pump shaft up, remove the case drain plug and spiral retaining ring, pry out the seal carrier, press in a new lip seal, and reinstall with a new O-ring on the front bearing. The pump does have to come off the machine.

Do pre-1998 and post-1998 Series 42 parts interchange?

Not always. The 1998 block point change altered the charge relief, charge pump drive, housing screw depths and loop flushing spool, and Danfoss says many parts, including the housing, are unique to each side of the change.

What is the case pressure limit on a Series 42 pump?

Service manual 520L0638 lists 3.4 bar (50 psi) rated and 10.5 bar (150 psi) maximum at cold start. The 2013 technical information 11022637 lists 3 bar rated and 5 bar at cold start.

Can I tow a machine with the Series 42 bypass valves open?

No. Danfoss says the bypass valves are only for moving a machine a very short distance at very slow speed, no more than 20% of top speed for three minutes.

About the technical information on this page. Figures, procedures and part numbers here come from manufacturer service literature and are provided for reference only. They are only as accurate as the factory data, and the revision we have on file may not be the latest for your unit. Always confirm against the current manufacturer documentation for your exact model and follow safe work practices. RestoPower is not responsible for damage, injury or loss resulting from the use or misuse of this information, or from incorrect assembly, adjustment, installation or operation of any unit.

Need the right kit, or the pump rebuilt?

Send us the full model code and serial number from the nameplate, or a photo of it. We reply with price, availability and lead time. If you would rather have the pump rebuilt, the work is done in our shop or through the RestoPower repair network, and we arrange getting the unit to the shop doing the work. The teardown evaluation is free and you get a firm, itemized quote before any billable work. Work done in our shop carries a 1-year repair warranty. In-stock parts ship within 24-72 hours, and in-stock parts carry a 2-year warranty.

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