U-joints are pretty cool for an inanimate object that is little more than steel, rubber, and a dab of grease. They allow transmit power to wheels while we steer around a corner and send power from a fixed transfer case down to a mobile axle. In fact, you can make a pretty good argument that without the U-joint we might not have four-wheel-drive vehicles or vehicles with long-travel suspension. Or at the very least, we wouldn’t have had them for as long as we have. Sure, there are other ways of transmitting rotational forces around a corner, but U-joints are one of the most reliable and cost-effective methods found in steering axles and driveshafts.
One of the rites of passage for just about any off-roader is having to change a U-joint. You can learn to do this when you absolutely have to, like on the side of the trail after a U-joint breaks, but it’s better to learn in the relative comfort of your driveway with a full toolbox, a work bench, a vise, and maybe even a garage. We have swapped U-joints on the trail, in parking lots, and in the dirt, and we have a few tips and tricks to help you with that first U-joint swap. Even if you’re an expert U-joint swapper, we may have a thing or two to show you.
The first step in swapping a U-joint is pulling the axle and gathering the tools. Pulling an axle is a topic for another article, but once it’s out you will need a few handtools and a hard surface to change the U-joint. You will need a large hammer, a small screwdriver, and two sockets. Not required but handy nonetheless is a pair of locking pliers (more on that in a minute). One socket needs to be smaller than the outside diameter of the U-joint cap. The other needs to have a hole larger than the U-joint cap. Spicer makes some of the best U-joints out there for your drive axles and driveshafts, so that’s what we normally use.
The next step in the procedure is to remove the U-joint retaining clips. There are three types. The most common type on drive axles are these C-clips. You can tap them loose with the small screwdriver and the hammer. Once they have moved a little you can pry them free from their groove. The most common U-joint retaining clip on a driveshaft is an external snap ring. Less common on a drive axle (usually with chromoly shafts) are full-circle snap rings. External snap rings are easy to remove with needle-nose pliers. Full-circle clips on chromoly axles have to be removed with 90-degree snap-ring pliers.
With the C-clips removed, put the axleshaft flat on the work bench and tap the stub shaft with the hammer next to the U-joint cap. This should force the stub shaft down relative to the U-joint. If a tap doesn’t move things, hit it a bit harder. Once the stub shaft has moved all the way down you should be able to remove the U-joint cap from this side. Flip everything 180 degrees and use the same method to push the other U-joint cap out the opposite side.
Now you will need your two sockets and the locking pliers, if you’re using them. Using the sockets and the hammer, drive the U-joint out of the inner axleshaft one side at a time as shown. The locking pliers save your fingers from missed blows with the hammer. Installing the new U-joint is basically the reverse of what you have just done, but we have a few tips that will make it go more smoothly.
To start installing the new U-joint, you first have to remove the U-joint caps. Be careful not to drop them or jostle them too much or the needle bearings in the cap could become dislodged. If any of the needle bearings (held in place with grease) fall out during installation they can destroy the cap and thus ruin the brand new U-joint. One trick is to make sure the U-joint cross is as far through the axle’s ear as possible, with the ear over the rubber seal. Then slip on one cap and hold the whole U-joint as far into the ear and cap as possible while you drive that cap into the ear. Then drive it in farther than it needs to go and install the C-clip to that side. That will help you get the other cap on the other side in the same manner, using the cross to ensure that the needle bearings stay in place. Drive in the other cap and install another C-clip. If the C-clip groove will not line up, a needle bearing may be out of place under one of the caps. If both C-clips are seated, then use the same trick for installing the U-joint into the stub shaft as shown here.
Here is a different view showing how the one cap has been driven too far into the axle ear just to help with installation of the opposite side’s cap. Install a C-clip on that cap, slide the last cap into place and drive it home. You may have to tap either cap once or twice with the hammer to center the U-joint in the axle so it turns with just a little resistance. You can also check out the video we made showing most of the process in the video that accompanies this story.