4WD not engaging, indicator light illuminating.

I have a 2007 jimmy which occasionally will not engage 4WD even though the dashboard light illuminates. I can eventually get it to engage by pressing the switch to engage 2WD and then 4WD a few times. Not a huge problem at the moment but a little worrying when stuck in the middle of a field.

Appreciated.

bryn

The light turns solid green or flashes?

Must check:

transfer box (4x4 command bulb)
vacuum solenoids
vacuum switch
vacuum lines
hubs

The bulb is a constant green. If it is the solenoids how do I check them.


Thanks

bryn

constant green means that vacuum circuit is ok.

check hubs and/or transfer box.

I thought it had cured itself but its come back. I can hear the diff engaging when I select 4x4 but the front wheels don’t actually engage. Constant green light when selected by the switch and same for 4x4L.
To dark this evening to start working on it but I shall check the vacuum hub pipes and hubs first thing. Can you point me in the direction of knowing if its the transfer box.

Much appreciated
bryn

Hubs do "clack clack" and transfer box does "wuuut"

When in 4WD lift front wheels and go under the car. Try if you can move/spin front driveshaft. If you can spin it than transfer box is not engaging. If you can spin it and wheels start to move then transfer box is not engaging but hubs are. If you can't spin the front driveshaft but can spin the wheels than transfer box is engaging but hubs are not.

I think I’ve managed to narrow it down to the vacuum system by using the fault finding section on the forum and its an intermittent fault as well just to complicate things. I have;
1, Jacked each wheel up in turn separately , selected 4x4 (light is on) and when in fault I can spin the wheel.
2, Taken of the hubs and checked the teethed collars (clicked them in to place and un clicked them) which are fine and resealed the hubs when back on.
3, Checked the vacuum pipe work for the obvious and cleaned the small air filter.
4, Checked all the connections to the axil/wheel housing.

When it does work I hear a wurr and double click the last click being the vacuum hubs engaging. When not working I don’t hear the final click of the hubs engaging.
Can anyone give me a few pointers and.................................I live in the Wetherby area and does anyone know a good 4x4 mechanic.

Appreciated bryn

Have you checked the vacuum valves? these are quite easy to clean an lube with WD40.
Also the locking hubs should not have any grease in excess or improper seal on the wheel hubs.

If you have access to a manual vacuum pump or a seringe, you can manually lock/unlock each hub via a hose and start from the wheels and move to the vacuum lines and valves to check where is the leakage.

I'm thinking also in fitting a vaccum probe on the sistem to have a live measurement of the pressure (negative) within the circuit, but still no feasible (I mean cheap ) is available.

Have you checked the vacuum valves?

Can you point me in that direction please and tips.

Once again thanks

bryn

Is this any good.?

www.bigjimny.com/mediawiki/index.php?tit..._vacuum_system_works