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Okay, I am thoroughly confused. Had a loose of power steering when Cummins installed new engine. they deny fault - say it was "already going". It may have been "already going", but it was still power and not Armstrong Power!!! Anyway it is there in low gear at high rpm, but not there normally and at lower rpms. I was thinking power steering pump (a special made by Vickers for Foretravel), but in researching I keep running across the Sheppard M100PDP1 steering box as a possibility. Was told that the the Vickers is not normally a problem, while several of the Sheppard boxes have been replaced. Just how does one determine which unit is at fault? Sheppard told me to take it to a International truck dealer to have the box analyzed. Says it should be a hour of service to test it. Says International truck dealers have all the proper tools and knowledge, while other shops don't normally.
I would bet (small amounts only) on the pump rather than the steering gear. We have had two failures on the Sheppard steering gear. Both were failures of seals. The power assist was not lost. Only time we lost power steering was after a catastrophic seal failure dumped so much oil that the pump had nothing to pressurize. Radiator fans and power steering both shut down. I've read about several replacements of the Sheppard steering gear. All were due to leaking seals rather than failure of the power assist.
Check the belts. The pump may not be receiving sufficient power from the engine because a problem with the belt drive.
Why not put a pressure gauge on the pressure side of the pump to see what is happening, would beat guessing.
Start by changing the hydraulic system filters. That will both insure that restriction in the filters is not the cause and also let you determine if there is metal in the system.
Don't have any hydraulic system filters on the U225. It does not have the hydraulic fan or pump like the U240 has. Only the Vickers power steering pump and Sheppard steering gear.
My coach is the same way (hydraulic pump for steering only) but inside the power steering reservoir there is a filter inside the bath. I would think yours is the same?
We have the hydraulic system that drives power steering and radiators fans. The filters are inside the reservoir. They are visible and accessible after you remove the top of the reservoir. Additional hints on changing them are here: Hydraulic Filter Replacement (http://www.beamalarm.com/Documents/hwh/hydraulic_filter_replacement.html)
Yours may be similar even though the system does not drive fans.
Yup, the PS system is separate (smaller diameter reservoir) than the one that drives the hydraulic fans (if side radiator).