10540 4wd staying engaged

Its a 1998 10540 with Zetor axle .The 4wd will not disengage straight away after turning it off. A loud clicking sound appears from left side front. Eventually the drive disengages. What is a likely cause and cure????

As no replies have come for a few days I though adding some comment may help.

I am not familiar with the 10540 so my comments could be well short of the mark.
Mechanically linked 4WD front axles often have the drive engaged with a sliding dog to provide the front drive.

The travel of the front wheels is always different to some degree than travel by the rear wheels. Gearing may provide a close match but as the front wheels steer then no perfect match can be had.

The result is quite marked friction on the sliding dog that provides the front axle drive due to the tension between the two axle drives. This tension and resulting friction can prevent sliding of the dog, to release the front drive.

Slippage at the wheel normally provides resolution of this tension. That is why mechanically locked 4WD should only be engaged on soft ground.

To disengage the 4WD usually means shifting the lever that engages the drive ( often spring loaded ) and moving the tractor forward or back, and sometimes turning the steering during movement so the tension resolves and the drive pops out.

This works more smoothly on some systems than others .
Not using 4WD on hard ground is the best answer I have found.

I am guessing about the 10540 so I hope this comment is not too misleading.

Thanks for your input. I am thinking along the same lines but also wondering if the spring is broken or weak. Have tried on soft ground and wet ground with same result.It does eventually disengage. Still cannot figure what the clicking sound is when 4 wd engaged and coming from the left hand front hub area.