At our Hydrostatic Pump Repair Site, we offer many types of Hydrostatic Transmission Repair and information relating to Hydrostatic Parts
Today we will discuss:

Electrical and Hydraulic Displacement Controls

Pumps with a date code of 86-13 or below, has a mounting screw that is located under the control cover. With these pumps, you will need to remove the four control cover screws using an internal hex wrench (5/32″) . Take the cover and gasket, there you will see the screw.

Pumps with a date code of 86-14 and above, all have the control mounting screws on the outside. Take off the four control mounting screws, using an internal hex wrench (3/16″).

Be careful removing the control off the pump housing.

Then take off the control sleeve from the pump.

On older production pumps, take the control inlet screen plug from the inlet passage next to the control sleeve bore, with a hex wrench (5/32″) to take it off with.

Control orifice plugs are in the threaded passages under the servo piston covers. Take off the servo piston covers and gaskets and remove the orifice plugs using an internal hex wrench (7/32″).

Put new O Rings on the bottom of the control housing. Using lubricant on all of the O Rings (making sure the petroleum jelly is clean before assembly). The control spool and sleeve are not sold separately.

Reinstall the control orifice plugs in their passages and put on new servo piston covers.

Install and torque the control inlet screen plug to 20 to 30 in lb. The earlier models pumps you will need to install a screen plug with a .156″ through hole.

Pumps that are prior to date code 86-14 use a plug with a thread that is different from later units.

Align the control sleeve so the slot will use the swash-plate feedback pin (slot positioned  toward the pump cover) and insert the sleeve into the housing.

Take the control spool and align it with the sleeve and put the control onto the pump housing. Put the four mounting screws and torque it to 10 to 11 ft lbs.

Pumps with date code 86-13 or below, put a new gasket and replace the control cover. Put the screws (4) in and torque to 18 to 24 in lbs.

On the neutral position of the control, readjust it.

This is on a Sundstrand Sauer Danfoss Series 40 M46

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