MF 390 steering problem.

dooroy wrote: »

A friend of mine has a 390T 4WD (1989) and for the past few months , when turning right , the power steering sometimes doesn't seem to help unless the engine revs are up a bit ; increasing the revs there is a 'knock' and the steering will turn right.
It was happening very rarely at first but is happening more often lately.
Turning left is never a problem regardless of revs.
I offered to post here to see if anyone would have come across this or could offer some advice.
TIA.

There are a number of issues that creep into steering of 300 series. The most common is wear in track rod ends in particular the rod on the steering ram which may be worn but also the casting it sits in may be too worn for a new rod end. It's easy to check, while sitting in driver seat and steering you can see movement in track rod end before wheel starts to turn. There is a repair bush kit. Issue only effects models with single steering ram.

Not sure about the "knock" if you are slowing and reving the engine to help steer there can be a big knock caused by the 4wd disengaging after releasing break. This knock can be felt through the whole steering system and even seen in a slight wheel movement. Only on models with electric 4wd engagement, these tractors engage 4wd to increase breaking power.

If the knock could be better described as a notch felt only in the steering wheel the issue is in the hydraulic system. Could be a filter, pump or orbital unit. There are 3 filters in most 390's one beside engine which should be replaced, one between pump return and gear box which should be cleaned and one under gear box also needs cleaning.

Issue described could be a combination of all above. But as it's only effect one direction I'd suspect orbital unit but I'd still clean/replace filters one check replace oil first. What happens if steering tractor at low revs while stationary? Dose steering move with little play in steering wheel? Or met whit resistance straight away?

Just another thought, were track rod ends replaced recently? I've seen some spurious ones that are too long and bind with steering ram when turning. Can be fixed with a grinder.