# 6640 4WD shifting issues



## RexTWD (May 31, 2017)

Hello all,

My 6640 is stuck in 4WD. Not too bad for the mud but not too good in general. Anyway, I tracked it to the solenoid that operates the transfer case. Power goes to the solenoid, but it doesn't work. I looked on the F/NH parts site and they list two parts there - a solenoid, pn CAR127831/81870291 and a hydraulic valve, pn E9NNF674AB/81867440. 

My tractor shifts in and out of 4WD with a switch which energizes the solenoid. Is the hydraulic valve made for a different set up or does it work with the solenoid?

Is there any way to make the 4WD shifting into a manual shift.

Thanks for any help, good sirs. I'm new here and am sadly ignorant.


----------



## Fedup (Feb 25, 2014)

Converting to some sort of manual shift is probably not an option unless you're into engineering and machine work.
The parts you listed are probably the complete valve assembly and the coil separately. Easy enough to test the coil, the valve itself may be a bit more complicated. The coil should come off easily enough with no mess. The cartridge will unscrew from it's bore in the drop box but will probably drain fluid for some time while removed.


----------



## RC Wells (Dec 26, 2008)

The all wheel drive is electrohydraulically shifted. Check the continuity of the solenoid as the usual failure is the solenoid only.

As for a manual conversion it is possible, but inadvisable and can lead to damage. The solenoid actuated hydraulic shift unit is set to apply a set amount of pressure to allow engagement and disengagement when there is essentially no engagement pressure relative to gear entrainment. A manual conversion would require the operator to only shift when the gear set was under no load, which means stopping and rocking the tractor back and forth until there was no load on the geartrain and feeling the way in or out of gear, just like our older generation of four wheel drive pickups, only with lighter duty gears that will not handle partial shifts or racking the gears on the move.


----------

