580sm+ powershift transmission, 4wd not disconnecting

[Eric Martin]

hello guys
i am working on a 2008 case 580SM+ backhoe w/powershift trany
the 4wd is not disconnecting, stays in 4wd all the time
I traced the power to the control module in the steering column. i have power from the switch to the control module, but not coming out. and i traced and checked the wires from the control module to the trany, then i put 12volts to that wire on the trany side of the module and that disconnected the 4wd. So it seems that the control module has a short on the 4wd function. Anyone have any thoughts, did i miss anything. That control module costs 10k!!!! from case. and is 20wks out

 

[alrman]

When the brakes are applied on those powershift models, 4WD is engaged.
Might be worth checking that out.

 

[Eric Martin]

Hey that’s a good idea, if that switch is stuck it could keep the 4WD engaged
I’ll leave u know

 

[Eric Martin]

i was trying to find info on what signals the trany control to connect the 4wd when braking....is it the pressure sensor on the brake line down on the rear axle?

 

[Eric Martin]

Is it these that switch the 4wd on and off?

 

[alrman]

Is it these that switch the 4wd on and off?

Correct!

 

[Eric Martin]

i finally got this project done:
thanks alrman that was the trick...i had a faulty sensor

 

[Eric Martin]

Also another question....now when its traveling in 2wd and you brake the 4wd connects. Like it did before, but now it clunks when it engages. it did not do this before it was run i 4wd solid for awhile
any ideas what could be the issue. does this i was seeing a diagram with a limited slip?. is there any synchro acting piece that could be worn
serial. num N5C393403
AXLE NUM

 

[JL Sargent]

I have to wonder if a certain amount of "clunk" is ok. There is bound to be some slack taken up when going from to 2wd to 4wd. I do know that John Deere put out a service bulletin about allowable clunk when engaging 4wd on some backhoes so it does happen.