Ignoring a failing u-joint can lead to more expensive problems down the road. Let’s talk about some of the most common things that happen when u-joints begin to fail:
1. Leaking Transmission The vibrations caused by a bad u-joint cause the driveshaft’s stub shaft to rotate out of round. This causes the transmission’s rear seal to fail. Fluid will leak out of the transmission. If the fluid gets low enough, the transmission will be damaged. The same thing can happen to a transfer case.
2. Leaking Differential A bad u-joint at the rear of the driveshaft can ruin the pinion seal, in the same way the transmission seal can be ruined. Gear lube can leak out of the differential, potentially causing damage to the ring and pinion assembly.
3. Damaged Bearings If they go on long enough, the vibrations from a bad u-joint can damage any of these bearings:
The transmission output bearing (if there is no transfer case) The transfer case output bearing
The pinion bearing
4. Broken Driveshaft The u-joint connects the propeller shaft to the transmission and rear differential. So when a u-joint begins to fail, the driveshaft can start vibrating or moving around. If the U-joint gets bad enough, the driveshaft can break free from the u-joint. The loose driveshaft will beat on everything it can reach while the truck coasts to a stop. The driveshaft will be damaged as well as other parts. At that point, your driver and load will be stranded on the side of the road. That means:
Tow bills Emergency repair bills Late delivery penalties or refunds to customers A lot of lost productivity So even if you have a hefty rainy day fund for towing, etc., driveshaft repair bills, lost productivity, and additional repairs may wipe it out.
5. Serious Collision U-joints tend to fail completely during hard acceleration. A catastrophic failure on a highway on-ramp, for example, can be a big problem. When that happens, the vehicle won’t have power and might cause a serious collision with the car(s) behind you.
