Caterpillar M50:
power steering doesn't energize like it should

I am working on a cat M50D that has a problem with the power steering system. The steering pump is very slow to power up when you start driving, infact some times you need to "saw" the whell back and forth to get it to start. I have several customers that have the Daewoo version (BC25 I think) of the same machine, and they never have this problem. I noticed that there is a pressure sensor near the orbital valve in the steering column; is the most likely cause of the problem, or is there some thing else that I should check out first. When the powewr steering does start up, it steers normaly and gives no indication of some thing like a worn out piston seal in the P/S cyl, but thats just a seat of the pants diagnosis.
  • Posted 11 Aug 2009 05:04
  • Discussion started by fixitandy
  • Pennsylvania, United States
Showing items 1 - 4 of 4 results.
i also have a cat m50d. power steering won't come on at all. power steering only works while running hydo's lift tilt s/s. i talked with the cat dealer they said they thought the logic board turned on and off low speed pump for p/s. so i removed the logic board and sent to flight systems. supposedly rebuilt it got it back today installed same problem. anyone got any ideas. turn key on main power contacter closes. but no p/s pump. turn hand wheel still nothing. use hydo's and p/s works. please help.
  • Posted 7 Jul 2015 09:30
  • Reply by mechNtraining
  • Oklahoma, United States
Do it Today or Tomorrow But You will Do it.
Pressure switch on steer valve is normally closed, then opens when you turn the wheel, motor should jog up to 2nd speed steering. unplug the switch and motor should speed up to 2nd speed steering. Priority valve and relief valve under floor plate.
  • Posted 14 Aug 2009 04:29
  • Reply by carl_v
  • Pennsylvania, United States
This machine has one motor that does double duty for hydraulics and P/S. runs at low sped for P/S, and full power for hydraulics, speed is controlled by the controller for low and a contactor for high. Bypassing the pressure switch will not tell me if ther is a problem causing low pressure in the steering hydraulics.
  • Posted 11 Aug 2009 22:27
  • Reply by fixitandy
  • Pennsylvania, United States
If it is that pressure switch, you can check to see what happens by bypassing the switch by shorting the wires together.
Is the power steer motor running? when they sit on the seat and chose a direction?
Does the contactor for the power steer motor move freely and have good tips?
I seem to remember this unit having a permanent magnet power steer motor, have you taken a good look to insure the magnets in the motor are in good shape and not broken?
  • Posted 11 Aug 2009 20:06
  • Reply by edward_t
  • South Carolina, United States
"it's not rocket surgery"

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