Combilift C4000:
Steering Creep

Hi there,

Our C4000 has a steering creep problem, and I need fresh advice:

The RHS steering cylinder was damaged (shaft bent) after an hydraulic pipe failed while the wheel was halfway through rotation. Under load, the operator moved forward with a wheel at 45degrees. This bent the shaft.

We bought a replacement shaft from Combilift agents and it was fitted.

Upon commissioning the machine, we noticed that the RHS front wheel has a "toe-in" position. When switching the direction control lever from Sideways to Forward, the wheel is rotated to face 100% forward (as expected), but after about 10 seconds it starts to "creep" to a "toe-in" position again.
Measuring on the RHS (primary) shaft, this equates to about 9mm of "creep".

I suspect the air is entrapped in the hose between the two cylinders.
Some advice from technicians was to repeatedly switch the direction control lever from Carousel mode to Straight mode so as to "work out" the air.

I'm sceptical about the "self bleeding" capabilities of the Secondary (LHS) and hose connection the LHS and RHS cylinder: my reasoning is that the volume of hydraulic fluid in the cylinder + hose (called the "Synchronised Oil") is more than that of the volume of fluid moved in on stroke (cylinder volume). Hence, how can the system ever get rid of air in the Synchronised Oil line?

I guess the question then boils down to: What is the proper bleeding procedure when installing a new steering cylinder?

Any thoughts?

Thank you!
  • Posted 14 Jan 2021 21:16
  • Discussion started by Marius_CT
  • South Africa
let's get technical
Showing items 1 - 2 of 2 results.
T in a small line from the back side of the LH steer cylinder to the front if it. Essentially bypassing it to allow air trapped between the two front cylinders to be pushed through. The only way the system can purge with out doing this is back through the RH steer cylinders built in purge valve which can be difficult sometimes.
You can also check the LH steer cylinder for bypassing by first setting the front wheels to 90 degrees in side mode. Shut the truck off. Cap and plug the front line on the RH steer cylinder. Mark tge chrome rod of both front cylinders. Turn the truck back on in LH side mode. Turn the steering wheel 2 full rotations clockwise. Then 2 rotations counter clockwise. Now check the marks made on the chrome rods. If either cylinder extends while the the line is plugged will be the one bypassing internally.
  • Posted 21 Jan 2021 01:10
  • Modified 22 Jan 2021 09:25 by poster
  • Reply by BLey
  • Ontario, Canada
Hi Marius.
If you need any help from Combilift go to the web site and you can either link to the technical help (scroll to the bottom and select "Technical Support", or you can chat on the "chat bot", and they will point you in the correct direction.

The correct way to purge the front steering system is as follows.
Park truck in safe location
Start the machine
Apply parking brake
Place the directional lever into sideways position (either left or right)
Let the wheels complete its directional movement
Place the machine on full acceleration.
Turn the steering wheel clockwise until you find the steering wheel come under pressure.
Turn the steering wheel through the pressure for approx. 1 min.
Release the steering wheel and release full acceleration from the machine.
Select forwards/reverse mode.
The 2 front wheels should now align correctly.
Process may need to be repeated.
Best to drive forward and backward after this to check as there may be some tension held in the rubber on the wheels depending on the surface.

Hope this helps.
  • Posted 20 Jan 2021 23:00
  • Reply by Richard_Irwin
  • Monaghan, Ireland

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