Getting To Know Your Driveline: U-Joints

How Universal Joints Help Connect Your Drive Shaft

Next up in our series of articles related to the driveline in your semi-truck, our experts have put together the following information on universal joints for you to read through. U-joints are a small but incredibly important component when making sure you can properly operate your vehicle without any discomfort. Read on to learn more about the u-joints in your semi-truck's driveline!

What Are U-Joints On A Semi-Truck?

A u-joint, or universal joint, is a piece that connects the driveshaft to the differential, and sometimes connects the driveshaft to the transmission or two driveshafts to each other. It's a cross shaped component with a bearing at each end. These bearings allow the drive shaft to move laterally and side-to-side.

What Does a Driveline U-Joint Do?

In semi-trucks, the rear axle and rear wheels move independently of the rest of the vehicle. This means that a direct drive shaft from the engine to the axle will flex as the vehicle encounters bumps. Universal joints compensate for that motion, making sure the driveshaft can spin freely, no matter the road conditions.

What Are The Symptoms Of A Failing U-Joint?

A failing u-joint will cause a clunking sound, especially when using the accelerator pedal. A worn-out U-joint will also cause vibration at certain speeds. This vibration emanates from the center or rear of the vehicle. Here are a few additional signs you can look for to determine whether you have a worn or bad U-joint:

1. Squeaking noise when moving forward or in reverse: The bearing portion of each universal joint twists with each rotation of the drive shaft. Because of this, grease can evaporate, or be thrown out of the bearing cup. If the bearing becomes dry, metal-to-metal contact is made, and the u-joint bearings will make noise when the drive shaft rotates.

2. A clunk and ringing sound when shifting from drive to reverse: This noise is an indication that the universal joint bearings have enough excess clearance for the drive shaft to rotate slightly, then stop when power is reversed. This can be attributed to the next stage of deterioration after insufficient grease in the u-joint bearings is determined.

3. Vibration felt throughout the vehicle when moving forward: Fast vibration indicates that the bearings have worn enough to where the drive shaft moves outside of its normal rotational path. This causes imbalance and vibration.

4. Transmission fluid leaks from the rear: If transmission fluid is leaking from the rear, it is often the result of a badly worn universal joint. At this point, the vibration has worn the transmission's tailshaft bushing and damaged the output shaft seal, leading to leaks of fluid.

5. Vehicle can not move under its own power: If the u-joint brakes, the drive shaft will drop out and no longer transfer power.

If you experience any of the issues listed above, it's important that you take your truck into a certified mechanic that can properly diagnose the issue and correctly replace the parts.

Read More About Drivelines

If you have been researching drivelines and would like to know more about some of the individual components that make up the system, we have several articles designed to help you do exactly that. Click on any of the links below to read more about each part!

· Getting To Know Your Driveline

· Getting To Know Your Driveline: Axles

· Getting To Know Your Driveline: Yokes

· Getting To Know Your Driveline: Clutches

· Getting To Know Your Driveline: U-Joints

· Getting To Know Your Driveline: Differentials

Shop Now For Semi-Truck Driveline Parts

For those looking into replacement parts for their semi-truck, you've definitely found yourself at the right location. No matter what driveline part you've been needing for your semi-truck, we have a full selection for you to choose from. Whether you are looking for clutches, axles, yokes, driveshafts, universal joints, or differentials, we'll have it from some of the most notable brands in the industry. Login or create an account to start saving on your next driveline component today!