4WD vacuum system does not engage the front wheels, with no error on dashboard

Hello,

I need your help in trying to help a freind diagnose an issue with the vacuum system for the 4WD drive on the front wheels of his Gen3 Jimny made in 2011.

He bought the car with non-functional 4WD. The car refused to enter 4WD mode (lights on the dashboard start to show and then they dissapear).
The initial problem was found to be broken wires to the transfer case switch. He replaced the entire switch and now the car enters both 4WD-H and 4WD-L modes (it can engage low range gears and moves slowly). Now there are no errors on the dashboard when switching to 4WD-H and 4WD-L - all appears to be normal.

However, none of the front wheels became engaged to the front axle when in 4WD-H nor in 4WD-L. He tested this by having one front wheel in the air and engaging 4WD - the wheel still rotates by hand when it should not.

He then replaced both the vacuum switches in the engine bay with original new ones obtained from Suzuki.

However, the problem still remains. This is when he asked me for help to write on this forum for him.
Any ideas on what next to check?

Could it be that something in the vacuum system is blocked so that the vacuum forms normally but the vacuum can not reach the wheel hubs to move the collars?
As far as I know, the usual issue with Jimny's vacuum system is that there is a vacuum leak, but in that case the 4WD lights on the dashboard would blink. They do not blink in this car - they shine constantly when in 4WD.

The front drive shaft is engaging right? its just the hubs that a re not engaging?

You should hear them click in and out if they're working right. 

My next step would be apply vacuum to the 2 x vacuum ports on the hub to see if that moves it. Diagram below from the manual. 

 

 

As you surmise, the light is controlled by the vacuum sensing switch, if a vacuum builds up in the pipe then the switch closes and the light can come on steady, so if the pipes are blocked a vacuum can build up but the hubs not work, or if the switch is bypassed to appear to be closed the light still works.

Jump in the car, start it up, wind the window down, and turn off the radio & heater fans.
Select 4WD. You should hear a Click-click from the hubs as they engage and the 4WD light will come on steady (there will likely be a noise from the motor on the transfer box too)
Wait a few seconds and select 2WD, you should hear a Clack-clack from the hubs as they disengage.

If you hear both hubs engaging and disengaging then probably one or both has the pipes crossed over .
Select 4WD engine running, and take off the hubs carefully, you can see if they are engaged or free, the splined collar inside slides outwards to lock and pushes in to free (you can easily turn it if it is free)


If you only hear one, then the other probably has a blocked pipe, someone changed the wheelbearing and got grease bocking the vacuum port or the hub seal ring is mangled from chiselling the hub nut off.

Then you can start getting the wheels off and doing the tests that Hughes posted.

With the hubs removed you can blow through the ports to clear any grease with an airline.


There is also the possibility that the hubs work, but the axle won't drive because one of the CV joints has failed, or the pinion gear in the diff has no teeth....