Toyota 8FDU25:
Cannot steer properly.

Hello, I a having an issue with a Toyota 8FDU25 and its steering. When it was first reported, the steering was completely locked. I had to tow into shop as it could not steer. I have since replaced the orbital valve (hydrostatic steering valve) as well as the oil/hydraulic oil pump. I have removed the top bolt and spring from the flow divider and inspected the spring for any loss in retention - no loss.

I checked the steer axle cylinder - by disconnecting the hydraulic oil lines (L & R) from the cylinder. I tried steering to see if fluid was come out of one line and not another, which the steering was still very rough. I am out of ideas, would it be the oil control unit? Or could it steel be the hydrostatic?

Thanks I advance.
  • Posted 8 Nov 2020 04:09
  • Discussion started by Angel_Mendez
  • Illinois, United States
- Thanks!
Showing items 1 - 4 of 4 results.
Problem has been been solved. Removed relief valve on oil control valve. One of the relief plugs was clogged with some type of gasket material.
  • Posted 19 Feb 2021 13:24
  • Reply by Angel_Mendez
  • Illinois, United States
- Thanks!
There is a relief valve on top of the orbit motor to set The steer pressure. Sometimes when it's turned CW a 1/4 turn , steering is corrected. Connect gauge to the P port with the adapter 09450-23320-71. Pressure gauge is 1/8 PT. But pressures have to be taken. Should be at 1170 psi for 2 to 3 ton units. Hopefully the hoses didn't soften up and cause debris to get into the system. Supply hoses are standard hydraulic braided hose and return is low pressure. 300 psi. The orbit motor is not recommended to be rebuilt If all else has failed.
  • Posted 13 Nov 2020 03:12
  • Reply by ron_k
  • North Dakota, United States
4kliftman
I am not aware of the pressure's going to the orbital. The facility does not have the fitting to attach, I have ordered - waiting on arrival.

I removed the relief valve bolt and removed the spring inside. I examined the spring for wear/tear & tension. I examined the housing as best as I could without a scope.

I lifted the rear, and (while lift is KEY OFF ENGINE OFF) tried steering - it was still rough.

Now, by me saying rough I mean when I turn the wheel slowly in either direction, it manages to move the tires smoothly - while I try to move the steering wheel quicker in either direction - the wheel stiffens up. I believe this is a hydraulic issue.

Upon further inspection I found that the hoses leading from the oil control valve to the orbital (I am assuming the oil supply hose [listed in Toyota's service manual as the "T" valve on the orbital]) were torn as well as the supply hose was constructed of normal coolant hose, not hydraulic hose. I have since ordered the replacement HYDRAULIC hoses and am awaiting delivery.

My hypothesis, is that the non-hydraulic hose on the "T" valve of the orbital was choking the hydraulic pressure to the orbital, which would explain the smoother steering on the lower pressure scale and tough/choking steering on the higher pressure scale.
  • Posted 13 Nov 2020 02:14
  • Reply by Angel_Mendez
  • Illinois, United States
- Thanks!
What are your pressures on the system? Should be 2450 psi - to valve body. Is there any issues in lifting? Next is steer pressures. Would make sure you don't have a relief valve issue. Not very common on these to lose steering. Jacked up you should be able to move steering without the engine running to determine hydraulic vs mechanical issue.
  • Posted 13 Nov 2020 00:15
  • Reply by ron_k
  • North Dakota, United States
4kliftman

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