My '02 Excursion 7.3L PSD recently got stuck in the mud and my friends who were present, were adamant that my 4WD was working; saying the front tires weren't turning or slinging mud. I noticed in 4 Low, I heard no change in engine RPM's. I began to wonder too, so I manualy locked the hubs. After eventually getting the truck out, I went back to auto on the hubs and 2WD for the drive home. Once at home, I put it on jacks stands and started it. I immediatly found out that even in 2WD the front driveshaft and axles turn but the tires don't (Didn't know that and assume this is correct). When I put it in 4 High, all four tires turned but I watched the Passenger side front turn slower and slower until it came to a stop. If you gave the truck gas, that tire "woke up" but clearly turned slower than the rest. Any ideas why or whats wrong with that tire???? I also noted that the hub switch on that tire is difficult to turn compared to the Drivers side front tire. Any help would be appreciated. Thanks.

 

You have a Dana 50 on the front if stock. It is an open differential, so I would say it is normal for one tire to spin and the other not.

If you have the hubs in auto, the truck is on jackstands and you switch to 4x4, you will need to spin the front tires for the hubs to be able to do their jobs and engage. They cannot engage without the tires turning, so the jackstands are keeping it from happening.

 

I do have a stock front end. What you are saying about an "Open" rear end makes sense. Although when it was on jack stands, I did not spin them, then spun on their own when my wife started the truck, put it in 4 Hi and gave it some gas. Any ideas why that hub switch is so hard to turn?? Thank you for your prompt response!

 

Welcome to guzzle's 4x4 Autolock Hub Lubrication Maintenance Web Page for the hub.

With an open rear end, or in this case front end, both tires will not normally spin. One will give way to the other based on resistance applied to the carrier in the center.

The system will not usually "lock in" unless the tires can turn and allow the spring in the hubs to apply pressure and seat the teeth of the hub into/onto the axle shaft and marry it up to the unit bearing and tire.

 

Thanks much! Sounds like everything is working OK, just got in over my head in mud that day!

 

Maybe you have a leak on the right side. Did you try the same test, wheels up but hubs manually locked? Maybe everything is ok but I'd check for leaks. Also if you have a vacuum pump, see if it holds vacuum at each wheel.

 

When you're in 2wd the front axle should not be turning with the rear axle. If everything is working correctly, when the hubs are in auto and the dash switch is in 2wd, nothing in the front end should move. If you turn the dash switch to 4 high, the front axle should spin but the wheels may not for the reasons NicMike said. Basically the dash switch engages the front axle at the transfer case and applies vacuum pressure to lock/unlock the hubs (when they are in auto).

I will say this though; when you had it on jack stands, if the hubs were locked and the passenger side front was still spinning slower then the rest, it is very likely that the unit bearing is on the way out, hence causing more resistance at that wheel, and as NicMike pointed out, it's an open diff. There is a method to grease the unit bearing using the ABS sensor hole, there's a write up in the tech folder about it. If you're auto hubs were set to auto, then you might want to try swapping them from right to left and see if the problem follows the auto hub. They come right out, just squeeze the metal clip with a pliers (or your fingers if it's not rusted in there) and it'll pop out, then pull the hub out. If it's stuck, give it a little shimmy side to side or a light tap with a hammer.