4WD Truck Pulls Left Then Right Then Left Then Right

The Problem

Every once in a while, my truck would pull left then right, then left, then right, and eventually settle down and not do it again for weeks. It started out as a very faint pull to one side, then the other. I thought something was wrong with the power steering gear box. Then I noticed it would sometimes start doing this after going around a corner. This week, I almost hit a curb going around a corner because the steering didn't return to center like it normally did. I had to force the steering wheel back to center.

Here's a video of the truck pulling left then right.  I was doing my best to keep it in a straight line, but it looked like I was weaving a little:

https://www.youtube.com/watch?v=SIU7SdVY1O4

Diagnosis

So I took a look under the truck. I found nothing wrong with any of the steering linkages. I had my son turn the wheel left and right as I watched the steering linkages move. Still nothing wrong. Well, my axle dust shields were shot, but that wasn't causing the problem.

I then jacked up the front axle so the front tires were both off the ground. I turned the manual hub lock on the passenger front wheel and found that the front right wheel would turn just fine as long as the steering was pointed straight. But when I turned the wheel either right or left, the wheel would jam. This was because two of the four joints on the U-joint were binding up.

Why the U-Joint Causes the Problem

This truck is a 2008 Ford F-250 with a solid front axle with U-joints at the wheels. When it's not in four wheel drive, the hubs are unlocked and the front axle doesn't rotate, so the U-joints stay in the same position and don't rotate when the truck is rolling.

When the wheels steer left or right, you can have only two of the U-joint bearings pivot with the steering while the other two don't turn. The axle may stay in the same position while driving as long as it's not in 4WD.

The problem shows up when the axle rotates a quarter turn and the seized U-joint bearings are now in the vertical instead of horizontal position. This makes steering more difficult and causes it to pull to one side or the other. Then when the axle rotates another quarter turn, the problem magically goes away and doesn't show up again for a while.

It's My Fault

I've had this truck for a year and a half and hadn't greased the U-joints in the front axle . . . ever. So I cleaned off the grease fittings and pumped some grease in the U-joints.

For a test drive, I kept the front right hub locked manually, but the switch on the dash was not engaged in four wheel drive. As I pulled out of the driveway, the steering wheel would pull as the wheel rotated. Then it stopped pulling as the grease worked its way into the U-joints.

This wasn't a Ford problem. It was because of bad ownership. The truck wasn't properly maintained and the U-joints lost their lubrication. This steering problem can occur on any similarly configured 4WD pickup with U-joints on the front axle, be it Ford, Dodge, Chevrolet, or other.