[Haulback]

2001 Grand Vitara, 125,000 km, 2.0 litre - new to me.
No 4wd light.

So, I just took the air pump apart, cleaned it, new o-rings and replaced hoses
Now light comes on and stays on in 4h and 4L, but I’m not convinced I am getting 4wd to all corners,
In gravel can spin the back tires and same going up hill in fwd or reverse., no spin on front wheels
But 4L works, it that it at least slows the truck as it should, but I still can’t tell if all wheels are driving or not.
Is it possible for low range to work and not have the front wheels powered?.
Thx

[shakes]

Yep.

That pump/diaphragm is the devil. If your thinking of keeping the car for any decent amount of off-road work, consider swapping g to manual hubs and a vitara or Sierra solid centre.

[fordem]

I'd say it's fairly unusual for the 4WD light to be on and the 4WD not working, and yes, it is possible to be in low range and not have the front wheels powered.

Let's look at those issues in reverse order ...

When the vehicle is in 2H, power is directed through the transfer case to the rear output shaft only; when you shift from 2H to 4H, what you're doing is engaging the front drive in the transfer case,so power is now sent to both the rear output shaft and also transmitted via a chain to the front output shaft, through the front drive shaft to the front axle, which contains a pneumatic freewheel clutch, designed to allow 4WD to be selected without the need to get out and lock freewheeling front hubs. Shifting from 4H to 4L, engages the low range reduction gear set, which, similar to 4H, drives both the front & rear output shafts. If for any reason there is no front drive, the rear drive will still be present in both 4H & 4L selections.

Let's look now at why there may be no front drive and what tests can be done to determine where the problem lies.

As mentioned before 4WD has to be selected in the transfer case for power to be sent to the front axle, so let's check that first - park the car where you can slide under it from the right side - set the handbrake and select 2H, slide under the car just behind the front tire and try to rotate the front drive shaft - you should be able to turn it. Now select 4H and repeat the test, this time you should not be able to turn the drive shaft - if you can, there is a problem in the transfer case.

When power is sent to the front axle, if the freewheel clutch is engaged, it rotates the front differential assembly and the front axle shafts - if the freewheel clutch is not engaged, nothing happens - to test this, jack both front wheels off of the ground, select 4H, switch the ignition on, make sure the 4WD light turns on, and try to rotate either front wheel - it should turn and the opposite front wheel should rotate in the opposite direction (because of differential action) - if this does not happen, there is a problem in the front differential.

The pneumatic freewheel mechanism is a known problem area, and most likely where your problem lies, so now let's take a look at that - you may need someone to give you a hand with this.

Disconnect the pump outlet tube (the one that goes to the differential) - have your assistant switch the ignition on and shift from 2H to 4H, the pump should start & run for about 10 seconds and then stop without the 4WD light turning on - now cap the pump output with your finger and have your assistant shift from 4H to 2H and back to 4H - this time the pump should start & run for 1~2 seconds and stop with the 4WD light on - you should also be able to start & stop the pump by uncapping & recapping the output, provided you don't let it run for more than 10 seconds. If you can do this the pump assembly is in good working condition.

If you've gotten this far and every thing checks out then the problem will be in the front differential.

[Haulback]

Fordem
Thanks for you timely reply and helpful advice . The front driveshaft would not rotate with 4wd engaged, so looks like all is well in the all wheels turning department. Thanks again.
How does the air pump like getting wet? There is a very good chance I will be fording some shallow river crossings in the next few months.
When I reassembled the pump I was very careful when replacing the metal cap and seal - I then over-wrapped the seam with self amalgamating tape to doubly ensure a good seal. Only other concern is the electrical connector ‘plug’
Ideas??

[Haulback]

Thanks fordem for your timely and helpful reply.
Checked the front driveshaft as suggested and it doesn’t turn when 4wd selected.
It looks like I have to strip down the air pump again, as with the hose to front diff disconnected the 4wd light stays constantly lit.thanks for the good troubleshooting advice ......I will put the rest of it to good use as time goes on.
Thx again

[fordem]

The air pump has several O ring seals, it'll survive the occasional short term immersion - if you've opened it, and you reassembled properly, you should be fine - the long term fix, as Shakes mentioned, is to fit manual freewheel hubs and lock the center engaged, either by welding, or replacing it with one from an earlier model.

Regarding the light staying on with the hose disconnected - make sure you have a good ground.

Bench testing the pump...

If you have a low pressure gauge (0~25 psi) connect it to the pump outlet and power the pump from a 12v battery, -ve to black, +ve to red - the pump should run for a second or two, build pressure to between 5~10 psi and then stop, with the pressure holding steady - disconnect the power and the pressure should immediately drop. Connect a small 12v lamp between pink & -ve and repeat the test - the lamp should light when the pump cuts off.

If you don't have a gauge, power the pump from a 12v battery, -ve to black, +ve to red, the pump should run continuously (don't let it run for more than a minute or so) and stop/start if you cap/uncap the outlet port with a finger - now connect a small 12v lamp between the pink wire & -ve - when you cap the outlet & the pump stops, the light should turn on. Without the gauge you don't know if you have enough pressure to actuate the differential clutch, but if it stops & starts properly, you should be OK.