JD 4400 power steering inoperative

[sprockets]

Everything else on the tractor works fine but the power steering has stopped working, any help?

 

[beenthere]

:welcome: to TBN

Will start with asking for some history... bought it new? How many hours? When last hyd filter, screen clean, new oil ?

 

[sprockets]

Used but have owned it many years, about 1770 on the hours, back end was taken apart last year to fix the Diff lock and filters were changed then along with all new fluid, aprox 80 hrs on it since then.

 

[texasranger556]

Do you have a hydrostatic transmission? The power steering pump supplies both the steering and hydrostatic drive, so if your transmission still runs smooth that would indicate you didn't grenade the pump.

Any noise when turning the wheel like increased engine load or hydraulics squealing over relief? What all have you checked?

 

[sprockets]

No noises and the hydro works just fine along with the bucket, pto, and lift arms, just no power steering. Unhooked both lines from the steering piston and turning either direction, left or right fluid comes out of both hoses which doesnt seem right, no warning with this, just stopped working.

 

[sprockets]

Is this system strictly mechanical or are there any relays or any thing electrical involved. Have had a couple of no start issues and wiggling the fuses and relays always seems to get it running.

 

[texasranger556]

Nothing electrical that I'm aware. This is the theory of operation from the service manual:

THEORY OF OPERATION
All Models:
The front hydraulic pump supplies hydraulic pressure to
the steering control unit (SCU). The SCU utilizes an
open center control valve to operate the steering
cylinder. When the steering wheel is turned, the SCU
directs hydraulic pressure to the appropriate steering
cylinder hose, pushing the steering cylinder ram, which
pivots the front spindles and wheels. The SCU has no
relief valve. The SCU and steering cylinder are not
rebuildable, and must be replaced as complete units.

Hydrostatic Model:
Excess oil from the SCU passes through a tee fitting on
the left side of the tractor, in front of the fuse panel. Oil
travels either to the oil cooler, mounted in the front of
the tractor, or directly to the hydrostatic unit. Oil
entering the hydrostatic unit passes through a cartridge
filter. The hydrostatic unit is a combination motor and
pump, and operates as a closed loop. Most of the
hydraulic oil delivered to this unit passes by the charge
pressure relief valve, and returns to the reservoir. A
small amount of oil flows through the hydrostatic unit,
providing internal lubrication, then returns to the
reservoir.

 

[sprockets]

Thank you, we will see what we find.

 

[Brown Dog]

My 4720 has a hex shaped inline filter screen located on left side, that was stopped up with 200hrs.

I removed it, cleaned with carb cleaner & it works perfect now.