Sundstrand Series 24, 25, 26 and 27 Pump and Motor Rebuild Guide: Teardown, Seal Kits, Torque and Start-Up

To rebuild a Sundstrand Series 24, 25, 26 or 27 heavy duty pump or motor, remove the shaft seal before touching the end cap, then the charge pump and check valves (or the motor manifold), the control, the spring-loaded end cap and valve plate, and the bearing plate and cylinder block kit. Fit the overhaul seal kit for your series and unit type, set shaft end play to 0.15-0.3 mm (0.006-0.012 in), torque to the Danfoss chart, and confirm charge pressure of 190-210 psi in neutral and at least 160-180 psi in stroke before the machine goes back to work.

These are the big frames of the Sauer-Sundstrand heavy duty family: 119, 166, 227 and 334 cc in Danfoss's newer frame codes. The procedure is the same as on the small frames, but almost every number changes: end cap torque runs to 393 N·m on the 227 and 334, end play doubles, the check valves and charge pump bolts get larger, and the 25, 26 and 27 Series went through a bearing plate redesign in 1985 that you have to respect when ordering plates. If your unit is a Series 20 through 23, use the Series 20-23 rebuild guide.

What this page is based on. Danfoss Series 20 axial piston pumps service manual L1003506 (Rev BA, June 2014), the Series 20 axial piston motors service manual L1003443 (Rev BA, June 2014), the Sauer-Sundstrand heavy duty service manual BLN-9630, the quick reference parts manuals for the variable pump (520L0910), fixed motor (520L0911) and variable motor (520L0912), and service bulletins BLN-9920, BLN-9592, BLN-9593 and BLN-9736. Where the documents disagree we show both figures. No wear limits for blocks, plates or slippers are published in any of them, and this page does not make any up.

How do you identify a Series 24, 25, 26 or 27 unit?

From the nameplate. The first two digits of the model number are the series, and the third digit is the type: 2 for a variable displacement pump, 3 for a fixed displacement motor, 4 for a variable displacement motor. Parts are ordered against the full model number.

Series	Danfoss frame code	Displacement	Max speed at max displacement	Main port flange (Danfoss code)
24	SPV2/119, SMF2/119, SMV2/119	7.24 in³ (118.6 cc)	2,700 rpm	3000 psi SAE J518
25	SPV2/166, SMF2/166, SMV2/166	10.12 in³ (165.8 cc)	2,400 rpm	6000 psi SAE J518
26	SPV2/227, SMF2/227, SMV2/227	13.87 in³ (227.3 cc)	2,100 rpm	6000 psi SAE J518
27	SPV2/334, SMF2/334, SMV2/334	20.36 in³ (333.6 cc)	1,900 rpm	6000 psi SAE J518

Sources: BLN-9630 page 3 (displacement and speed; maximum recommended working pressure 5,000 psi, 345 bar, for all four); L1003506 page 4 (flange code by frame); 520L0910 to 520L0912 (frame codes). Sundstrand says 6,000 psi (414 bar) operation requires welded (non-filled) pistons.

The serial number tells you which parts list applies. Its first two digits are the dash number, which changes when a design change affects interchangeability, followed by the build year and month or year and week. On these frames the dash number is not trivia: it is how you know which bearing plate design is inside a 25, 26 or 27 Series unit (see below). Our Sundstrand and Sauer-Danfoss identification guide covers the date code rule in general.

What changed on Series 25, 26 and 27 bearing plates in 1985?

Sundstrand developed a bi-metal bearing plate for the 25, 26 and 27 Series. It is thinner than the original, so it needs a thicker valve plate and a different pilot ring. Per BLN-9920 it went into new 25 Series units on January 1, 1985 and into 26 and 27 Series units on March 1, 1985, and the dash number (first two digits of the serial number) changed to 15 on all of them.

The new bearing plate must be used with the new valve plate and the new pilot ring. If an old-style valve plate or bearing plate needs replacing, all three are replaced together.
The old plates are no longer made. Order an old valve plate or bearing plate and you get a kit with a new valve plate, bearing plate and pilot ring: 9510640-025R, -025L and -025M (right hand, left hand and motor) for the 25 Series, 9510640-026R, -026L and -026M plus indexed 9510640-I26R and -I26L for the 26 Series, and 9510640-027R, -027L and -027M for the 27 Series.
An old cylinder block kit is replaced by the new block kit plus the new valve plate for your rotation.

New configuration (dash 15 and later)	25 Series	26 Series	27 Series
Valve plate, right hand	9250652	9260355	9270683
Valve plate, left hand	9250653	9260356	9270684
Valve plate, motor	9250629	9260357	9270655
Bearing plate	9250627	9260321	9270657
Pilot ring	9250628	9260358	9270656
Cylinder block kit	9250685	9260369	9270658

Source: BLN-9920 Rev AB (2013), pages 2-4, which also lists double pin and special slipper retainer variants. The 2015 quick reference parts manuals show different numbers for several of these parts (for example 651810 and 628933 for the 25 Series pump valve plates, and 651844 for the 26 Series motor plate). We do not guess which number supersedes which; send the serial number and we match it.

How do you tell if a Series 24-27 needs a rebuild or just a valve?

Symptom	Check first (per BLN-9630 and L1003506)
Drives one way only	Control linkage, then interchange the system relief cartridges and then the charge check valves. If the problem follows the part, replace it. Then the shuttle valve and the control.
Low charge in neutral, fine in stroke	The charge relief in the charge pump (debris under the poppet, galled seat).
Low charge in stroke (under 160 psi), fine in neutral	The charge relief in the motor manifold. It must be set below the pump charge relief or the loop cooling circuit stops working.
No drive either way	Oil level, control linkage, motor bypass valve if fitted, charge pressure, inlet filter, then the charge pump.
Overheating	Oil level, heat exchanger, inlet filter, bypass valve, and system pressure against the load.

The full fault logic with gauge readings is in our hydrostatic transmission troubleshooting guide, and the case drain flow test is the best check for internal wear before teardown.

What order do you take a Series 24-27 pump apart?

These are heavy units. Danfoss recommends lifting by the rings at the front and rear of the housing and working on a mounting block (dimensioned in L1003506). Clean the outside, cap every port, and protect every sealing face.

Shaft seal first. Remove the large retaining ring, side opposite the tangs first, pry out the aluminum seal retainer (held by its O-ring) with the stationary seal and springs, and work the bronze rotating ring off the shaft by hand. The end cap screws stay tight until the seal is out.
Charge pump. Loosen the four screws in the rectangular pattern only; the top and bottom screws hold the pump sections together. Watch for the idler shaft spacer on aluminum body pumps. Discard the gasket.
Charge relief and check valves. Plug, spring and poppet come out with a 1 in wrench. Leave the shims alone on shim-adjusted valves unless parts are replaced. The check valves are threaded cartridges under the charge pump; use a draglink socket and keep them in position.
Control. Nine cap screws (7/16 in wrench). Unhook the control pin from the swashplate link and keep the gasket, three O-rings and orifice plate out of the housing.
End cap. Remove all but two screws, then loosen the last two alternately to let the internal spring load off. Hold the valve plate as the end cap separates. Pump plates are rotation specific.
Rotating group. Lift out the bearing plate and pilot ring. Pull the tapered bearing off the shaft with a puller (80 x 120 mm and 200 x 250 mm pullers are on Danfoss's tool list), using a spacer to protect the slot in the shaft end, then lay the unit horizontal and slide the cylinder block off while holding the shaft.
Swashplate, servo and shaft if needed. Front cover off, shaft and bearing out. Mark servo cylinder depth and sleeve position, mark each trunnion and keep its plastic shims with it, then lift out the swashplate with the servo piston. Danfoss lists 36 to 65 mm open end wrenches for the servo cylinders.

Motor differences

On fixed and variable motors the valve manifold carries the system relief cartridges, shuttle valve and second charge relief. It seals with O-rings and back-up rings, not a gasket. On 166, 227 and 334 frames the manifold is the large valve version with a much higher bolt torque (see the chart). Relief cartridges swap side to side when the settings match, and the shuttle spool is matched to its manifold. Motor valve plates have four tapered slots; pump plates have two.

What do you inspect inside a Series 24-27 pump or motor?

Shaft seal: always replace both halves together and keep the lapped faces spotless (BLN-9593).
Valve plate and bearing plate: damaged plates are replaced. On 25-27 Series, check the dash number and replace the bearing plate, valve plate and pilot ring as a set if the unit is pre-dash 15 (BLN-9920).
Thrust plate: any surface damage means replacement; the chamfered side goes toward the swashplate.
Cylinder block: replaced complete or in part depending on the damage.
Bearings: a damaged shaft bearing means a new cup in the front cover or housing as well.
Charge pump and control: inspect the relief valve cone, seat and spring, and make sure the shaft and gears turn freely. Danfoss does not permit further disassembly of the charge pump or servo valve.
Charge check valves: slight spring resistance on the ball and a clean return to its seat. Replace in pairs.
Shuttle valve: a sticky, worn or cracked spool means a complete manifold.
Pistons: welded pistons are the service part. Fitted into a block with other piston types, they go in symmetrically in multiples of three; units built with welded pistons stay welded, and solid pistons never go into a unit that did not have them, because they cut speed capability by about 20% (BLN-9736).

Scoring, slipper wear and swashplate damage are judgment calls; Danfoss gives no limits. On parts this expensive, get the rotating group evaluated before you buy.

Which overhaul seal kit fits a Series 24, 25, 26 or 27?

Part	Series 24 (119)	Series 25 (166)	Series 26 (227)	Series 27 (334)
Overhaul seal kit, variable pump	9510236	9510239	9510316	9510242
Overhaul seal kit, fixed motor	9510237	9510240	9510317	9510243
Overhaul seal kit, variable motor	9510238	9510241	9510318	9510244
Shaft seal kit	050302	050302	058537	050534
End cap gasket	9240549	9250587	9260144	9270710
Charge pump gasket, gear pump	9801604 (all four)
Charge pump gasket, gerotor pump (not in overhaul kit)	9803241 with IPOR, 9803252 without	n/a	n/a	n/a
Charge check valve assembly	075366	543553	543553	543553
Control gasket	9803340 (all four)
Motor manifold O-ring kit	9510049 (all four)

Source: Danfoss 520L0910 page 7 (pumps), 520L0911 page 5 (fixed motors), 520L0912 page 7 (variable motors). The linked kit is one we carry; the rest we source against your nameplate. Note the charge pump gasket: 24 through 27 Series take 9801604, not the 9801235 used on Series 20 through 23.

Hard parts from the same manuals: pump valve plates (CW / CCW) 004895 / 004903 on the 24 Series, 651810 / 628933 on the 25, 9260355 / 9260356 on the 26 and 622324 / 651968 on the 27; motor valve plates 9240279, 9250629, 651844 and 9270655; cylinder block kits 9240641, 634923, 9260369 and 9270658. For 25-27 Series units, read the bearing plate section above before ordering any of these. We also carry the 24 Series trunnion shim kit 9510422-0005 and a 26 Series 13 tooth pump shaft; see the Series 24 and Series 26 parts collections and the Sundstrand seal kit collection.

What are the Series 24-27 torque values and end play?

New gaskets and O-rings everywhere, lubricated with clean petroleum jelly, and clean oil on the thrust plate, slippers, pistons and bores.

Splines: the undersized tooth in the cylinder block spline lines up with the missing tooth in the ball guide and the missing tooth on the shaft.
End cap: valve plate slot over the end cap dowel pin, end cap turned so the housing dowels find their holes, drawn down evenly with two opposing screws before the rest go in.
Neutral: with the trunnions back on their original shims and the servo cylinders at their marked depth, check the thrust plate with a depth micrometer at two points 180° apart, 90° to the trunnions. Danfoss allows the readings to differ by 0.03 (no unit printed). Peen the retainers into the locking slot afterward.
Shaft end play: 0.15-0.3 mm (0.006-0.012 in) on 119 to 334 frames, set with a shim under the bearing race in the end cap. Check it whenever the shaft, bearings, housing, front cover or end cap change. The shaft seal goes in last.
Shaft seal: bronze ring lapped face out, stationary seal notch on the retainer pin, retaining ring beveled side out. Spring count is eight on 24 and 25 Series, ten on 26 Series and twelve on 27 Series (BLN-9593).

Fastener	Series 24 (119)	Series 25 (166)	Series 26 (227) and 27 (334)	Sauer-Sundstrand figure
End cap screws	90.9-111.2 N·m (805-984 lbf·in)	181.7-223.7 N·m (1608-1980 lbf·in)	325.4-393.2 N·m (2880-3480 lbf·in)	Not given
Front cover screws	90.9-111.2 N·m (805-984 lbf·in)			Not given
Charge pump screws	36.6-50.2 N·m (324-444 lbf·in)			27-37 ft·lb (BLN-9630, BLN-9592; 3/8 in UNC)
Charge pump suction port	20.6-31.4 N·m (182-278 lbf·in)			Inlet hose 14-21 ft·lb maximum
Charge check valves	108.5-122.1 N·m (960-1081 lbf·in)	169.5-183.1 N·m (1500-1621 lbf·in); 108.5-122.1 N·m with the 32.8 cc (2.00 in³) charge pump		24 Series 80-90 ft·lb; 25-27 Series 125-135 ft·lb
Servo control valve screws	13.6-14.9 N·m (120-132 lbf·in)			10-11 ft·lb
Spring assembly	21.7-28.5 N·m (192-252 lbf·in)		36.6-50.2 N·m (324-444 lbf·in)	Not given
Servo piston locking screw	40.2 N·m (356 lbf·in)			Not given
Motor valve manifold screws	21.7-28.5 N·m (192-252 lbf·in)	90.9-111.2 N·m (805-984 lbf·in), large valve manifold		16-21 ft·lb
Pump charge relief plug	22-24 N·m (195-212 lbf·in)			30-60 ft·lb
System relief cartridges	Not given			30-70 ft·lb
Shuttle hex plugs and motor charge relief plug	Not given			60-100 ft·lb

Sources: Danfoss L1003506 page 35 and page 22, L1003443 page 22, BLN-9630 pages 28-30, BLN-9592. Sundstrand's manifold and relief figures in BLN-9630 are written for the whole heavy duty family. The two manuals disagree on the pump charge relief plug (22-24 N·m against 30-60 ft·lb), so check the current manual for your unit.

What should charge pressure be on a Series 24-27?

The same as the rest of the heavy duty family. BLN-9630 lists 190-210 psi (13-15 bar) in neutral and 160-180 psi (11-12.5 bar) in forward or reverse, above case pressure, with a note that some machines use special settings. The pump charge relief sets the neutral figure; the second relief in the motor manifold sets the in-stroke figure and must stay below the pump relief. The 2014 Danfoss manual L1003506 puts it at about 15 bar (217.6 psi) in neutral at 1500 rpm, about 2 bar lower in stroke, and says to stop and troubleshoot below 8 bar (116 psi).

System requirement (BLN-9630)	Value
Charge pressure, neutral	190-210 psi (13-15 bar) above case
Charge pressure, forward or reverse	160-180 psi (11-12.5 bar) above case
Case pressure	40 psig maximum (3 bar)
Inlet vacuum	10 in Hg maximum (0.7 bar absolute), cold starts excepted
Suction filtration	10 micron nominal, no bypass, Beta 10 = 1.5 to 2.0

Use snubbed, calibrated gauges: 500 psi for charge and case pressure, 10,000 psi for system pressure, and a vacuum gauge in the inlet line.

How do you start up a rebuilt Series 24-27 transmission?

Check both units for handling damage and clean the reservoir, hoses, valves, fittings and heat exchanger.
Fill the reservoir through a 10 micron (nominal, no bypass) filter with new fluid, fill the inlet line, and make sure it is tight and free of restrictions.
Fill the pump and motor housings with filtered oil through the uppermost case drain port.
Fit a 500 psi gauge to the charge pressure port. Leave the control linkage disconnected so the pump stays in neutral, and secure the machine against movement.
Run at the lowest rpm until charge pressure builds. Bleed air from the high pressure lines at the gauge ports on the motor manifold.
Raise to operating speed and confirm at least 190-210 psi charge pressure. If it is not there, shut down and find out why.
Connect the linkage, restart, confirm the pump holds neutral, then cycle slowly between forward and reverse for five minutes while charge holds at least 160-180 psi.
Shut down, remove the gauges, plug the ports and top up the reservoir.

Source: BLN-9630 page 7. Fluid change intervals in BLN-9630 are 2,000 hours on a sealed reservoir and 500 hours on an air-breathing reservoir, unless the machine maker specifies otherwise; the 2014 Danfoss manual asks for the first change at 80-100 hours on a new system, the second by 500 hours, then every 1,000 hours or once a year. See our pump start-up guide and fluid cleanliness and flushing guide.

Should you rebuild a Series 24-27 yourself?

Seals, charge pumps, check valves, controls and manifolds are fair game for a good shop with big torque wrenches. The rotating group on these frames is expensive to get wrong: a pre-1985 bearing plate paired with a new valve plate, a pump plate in a motor, or end play never rechecked after a bearing change will cost you the parts all over again. If there was metal in the filter, have it torn down and quoted first. For the other Sundstrand lines see the Series 90 pump rebuild guide and the Sundstrand seal kit guide.

Frequently asked questions

What seal kit fits a Sundstrand 26 Series pump?

Danfoss lists overhaul seal kit 9510316 for the 26 Series (SPV2/227) variable pump. The 26 Series fixed motor takes 9510317 and the variable motor 9510318. The third digit of the model number tells you which: 2 is a pump, 3 a fixed motor, 4 a variable motor.

Which charge pump gasket fits Series 24 through 27?

Gasket 9801604 fits the gear-type charge pump on 24, 25, 26 and 27 Series, per Danfoss parts manual 520L0910. Series 20 through 23 use 9801235 instead. A 24 Series with a gerotor charge pump uses 9803241 with IPOR or 9803252 without, and those are not in the overhaul kit.

What is the shaft end play on a Series 24-27 pump or motor?

Danfoss specifies 0.15 to 0.3 mm (0.006 to 0.012 in) for 119 through 334 frames, which are Series 24 through 27. It is adjusted with a shim under the bearing race in the end cap whenever the shaft, bearings, housing, front cover or end cap are replaced.

What torque do Series 26 and 27 end cap screws take?

Danfoss L1003506 gives 325.4-393.2 N·m (2880-3480 lbf·in) for the 227 and 334 frames, which are the 26 and 27 Series. The 25 Series (166) takes 181.7-223.7 N·m and the 24 Series (119) takes 90.9-111.2 N·m.

Can I put a new valve plate on an old Series 25, 26 or 27 bearing plate?

No. Per Sundstrand BLN-9920, the bi-metal bearing plate introduced in 1985 is thinner and needs a thicker valve plate and a different pilot ring. If an old-style valve plate or bearing plate needs replacing, all three parts are replaced together. Units built after the change carry dash number 15.

What is the charge pressure on a Sundstrand Series 24-27?

Sauer-Sundstrand BLN-9630 gives 190-210 psi in neutral and at least 160-180 psi in forward or reverse, above case pressure, for the whole heavy duty family. The 2014 Danfoss manual L1003506 states about 15 bar in neutral at 1500 rpm, about 2 bar lower in stroke.

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 unit rebuilt?

Send us the model number 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 or motor 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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