EX50 No 4WD lost drive to front end

[XCAT]

Hi all,
we have a Daedong EX50 @ 700 hrs - i think you would know it as a DK45 / 50. very well serviced.
working to day and noticed that it lost 4WD, no noises heard - so off to the workshop to check it out,
have checked all electrics and found fuses ok, power and earth at the 4wd solenoid on the modulator valve ok and you can hear the solenoid click when you unplug and reconnect the loom.
lifted tractor up and removed front drive shaft tube cover and checked that the drive line is ok to the wheels - so no broken bevel gears or diff.
i have pressure tested the line and 4wd clutch pack piston and it is holding pressure so no leaks internal.
I then checked how much oil comes out of modulator valve at the connection for 4WD line and --- not much at full revs with the 4WD switch on.
so i loosened ( did not remove ) the supply pipe nut from the pump to modulator valve and not much oil comes out of there either.
so although maybe most oil may still be going back to trans via the modulator valve , i would have thought that oil should have come out under pressure from the pump supply pipe.
so i am thinking that the steering - pto - 4WD pump may have given up. steering still works but i think i am feeling it a bit rough.
has anyone else had any issues with the steering pump? the main pump is working fine...
any thoughts - any ideas greatly appreciated
thanks

 

[Agvg]

Are you sure the pressure engages 4WD?
Most common to use the pressure to disable 4WD.

 

[XCAT]

Are you sure the pressure engages 4WD?
Most common to use the pressure to disable 4WD.

Hi thanks for the reply - YES i am sure - needs pressure to activate either 4WD or PTO. default is no 4WD or PTO

 

[XCAT]

I have re thought the hyd and will need to make a fitting to check for full pressure.
i have read the genuine manual and the valve will not open fully with just flow as it has a pilot valve, sequence valve and reducing valve built into the modulating valve.
it can not open valve fully without pressure building in the line. This is to make a soft start to the pto and 4wd to prevent damage.
i will need to make a fitting and retest.

 

[XCAT]

ok some news,
i tested with pressure gauge today and no pressure at all from the 4wd port - two days ago i had some flow but none today, tractor still has some steering so i dont think the hyd pump is at fault.

so i removed the modulating valve and stripped it down slowly and bagged each valve assembly as some of the springs are very similar.
when i removed the 4WD solenoid valve i found what i hope is the problem. The screen mesh, washer and cir clip were floating around inside the housing.
the reducing valve was hard to remove as the washer etc has been hitting it and caused burrs - i hope i can clean it up to reuse.
when i look at the method Daedong have used to hold the screen in place is a bit of a joke, the groove that the cir clip should sit in and be retained would be lucky to be only .002" deep. i checked the pto valve and it is the same and to top it off they have put the cir clip upside down ( the sharp edge of the cir clip should face out to help it from poping out.
so i intend to see if it all cleans up ok and i will try and deepen the groove in the lathe.
i hope this may help others if it happens again, i hope it works again as a new valve is around $1700.00 AUD

 

[XCAT]

so i machined a deeper groove into the solenoid valve to keep the cir clip in place on both the pto and 4wd valves.
spent around two hours carefully cleaning up the damaged spools, and hand lapping and all went back together well,
put it back on tractor and everything work again and steering is better also.
so i guess the steering oil was being lost via the drain on the 4wd solenoid
cheers

 

[mmecsics]

Wow, nice job.

 

[Kioti Paul]

Excellent job trouble shooting the problem! Very impressive. Because I have a DK45, I particularly appreciate the write up...so far, I've had no problems with my 4WD, but you never know.