Another 4wd problem

7mill · #1 05-30-2005, 04:40 PM

my 1998 f150 shift on the fly four wheel drive is not engauging. any ideas on what to check. The 4X4 light comes on but the front tires dont drive

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Colorado Osprey · #2 05-31-2005, 11:10 PM

Does the t-case sound like it is trying, and does the 4x4 light come on? How about low range?

If the 4x4 lights up, but doesn't engage, get underneath and check that the front drive shaft is really locked up by trying to spin it. If the T-case is locking the front drive shaft, then the problem is in the front axle. If not it is a t-case engagement problem. There is a selenoid in the t-case that can and does go out that pushes the t-case into 4x4.

AFTERTHOUGHT:

Have you tried it in neutral while stopped? Sometimes things just need time to lock up.

ALSO: as good maintenance you should have been shifting into 4x4 at least once a month for a mile, just to get everything moving. Try low range at least once every 6 months (NOT ON ASPHALT OR CONCRETE), for a few yards.

a2zl · #3 06-04-2005, 12:07 AM

the same thing happened to mine a few years back. their is a shaft and vacuum pot on the front diff that needs to rotate to engage the front end. In mine the shaft was seized in the case. I removed the front diff, tore it all down freed up the shaft and put anti seize on it,Its been ok after. Just check to see if everthing is moving when you engage 4wd.

7mill · #4 06-04-2005, 01:25 AM

The light comes on and the front drive shaft moves when its in four wheel drive. The front drive tires still dont drive

fordninja · #5 06-05-2005, 12:39 AM

There is a vacuum line that goes from the front diff to the engine compartment. I would check that for any cracks or holes or maybe it is unplugged. These truck use vacuum to lock the front diff. Let us know what you find!!!

GIJoeCam · #6 06-07-2005, 10:29 AM

Indeed, there's a center-axle disconnect. It's actuated by a vacuum solenoid on the passenger side firewall controlled by the GEM. That system is the most common failure point with the 4x4. If the light's coming on, the t-case is shifting. If the front axle fails to lock, it won't drive the front end.

-Joe