Whenever you jump in your rig and go barreling down the highway or over your favorite flavor of off-road terrain, you’re asking a lot from the shafts and joints spinning rapidly underneath. Of course, we’re referring to the driveshafts that transmit our engine power to the axles. Every time these rotate, each U-joint speeds up and down in angular rotation while moving in an assembly of needle bearings and grease.
These components should be checked on occasion and require periodic maintenance to ensure they don’t fail at the most inopportune time. Joints either come with or without zerk grease fittings. Those without are pre-lubed from the supplier to last the life of the joint. Those with a grease fitting should receive a squirt of grease from time to time.
Driveshaft carnage comes in several forms. You can, of course hit a rock or other obstacle with the shaft and bend it, or severely scar it. But you can also destroy them (and cause other collateral damage) by having one that is too short or too long in your drivetrain. Whenever you lift or modify your rig you should consider the effects those suspension changes may have on the driveshaft angle and length, and you just might save yourself from broken parts.
Those of us with solid front axles on (rear shackled) leaf springs often check driveshaft travel on the front axle to ensure there is sufficient spline length left engaged once the axle is fully drooped. However, a simple driveway check may not be sufficient to determine if you have adequate spline travel. On a vehicle with rear spring shackles on the front packs, the axle will want to droop down and move forward. When this is combined with a little throttle, the spring wrap induced by the front driving tires can stretch the packs down further, pulling the axle even further forward. This is when you’ll determine if your front shaft has sufficient spline travel.