How to grease U joints and How it Works?

Mechanical joints are essential parts of any automated mechanism. Joints are used to attach two moving surfaces (usually shafts). Joints allow a limited range of movements depending on the design. One of the widely used joints in the automotive world is U-Joints. U-Joints are used for many applications in cars. They are mostly used in rear-wheel drive and four-wheel drive vehicles. In this article, we are going to learn more about Joints, how they work, the problems related to them, as well as how to grease U-Joints.

u joints greasing

How do U joints work?

Universal joints consist of two yoke supports. Each pair of these supports is positioned at a right angle facing each other. They are connected by a midway cross-pin member called a spider. When assembled, pairs of cross-pin legs are supported by needle roller caps mounted in each yoke support.

This permits each yoke support to swing at right angles to the other yoke. Universal joints have to be strong and ideal for heavy-duty work. The U- joints are made by different manufacturers and come in various sizes to fit all applications. Therefore, when choosing a U-Joint, you have to be sure of its quality and size.

Before we introduce you to the assembly and internal parts of U-Joints, we have to know how they work and their role in power transmission. In rear-wheel or four-wheel drive vehicles, the power should be transmitted from the transmission in the front end of the vehicle to the rear wheels.

This happens through a power transmission mechanism that deploys a shaft, which comes from the transmission all the way to the deferential. The rear axle swings up and down as the car pass through bumps and potholes along the way.

U-Joints, allows the rotational energy of the engine to be transmitted from the gearbox to the rear axle of the vehicle. This is due to the constant change of the angle between the transmission and rear axle as you drive. U-Joints are required to keep them connected and also ensure there is minimum energy waste.

Just like other parts in a vehicle, universal joints require regular review to ensure optimum and smooth running. U-Joints can fail due to vibration and heat under normal driving conditions. Having an unbalanced driveshaft can also cause premature U-Joint failure. The bad greasing or failure to grease the U-Joints properly during periodic maintenance can also cause damage.

In my view on periodic maintenance skills, you need to know how to check U-Joints and how to diagnose the bad ones. Bad U-Joints have a common symptom, which is a high clunking noise when starting from a stop and vice versa. You will also note increasing vehicle RPM and harsh vibration, which keeps worsening at high speeds. The other symptom is a slight lag when starting from a stop. These symptoms are a warning that you may face a problem if you fail to fix it.

How to grease U joints Step by step guide

The most common cause of U-Joint failure is to run it dry or degreased. Your periodic maintenance schedule should include greasing U-Joints to prevent joint failure. The goal of greasing universal joints is to keep a clean layer of grease around the needle bearings. This decreases the metal to metal contact, grinding, and wear out. It is advisable to grease U-Joints is during every oil change if you are riding your car in a good environment. To grease U-Joints in your car properly, follow the instructions below:

Step 1: Access Rear Axle:

After lifting your car using a floor jack, let it sit on the jack stands. Use a creeper or wood/cardboard to slide under the car, then locate the rear axle.

Step 2: Find Out the Grease Fitting Point:

Underneath your car, find out the point where the driveshaft meets the rear axle. This is where the U-Joint is located. The grease fitting point is located in the center of the U-Joint. If you cannot see the grease fitting point, rotate the drive shaft slowly by hand in the grease fitting direction until you reach it properly.

Step 3: Grease U-Joint:

Using a grease gun and the right size grease gun coupler, start filling the grease into the filling home. Continue filling the grease until you see clean grease coming out of the filing place. Remember to always use a certified moly Grease for U-Joints such as Grease-u-joint or Spicer U-Joint grease. Those are the best certified universal joint greases in the market that gets this job done perfectly.

Step 4: Grease the Front Driveshaft U-Joints (if equipped):

If you are driving one of those four-wheel-drive vehicles, you have to get the job done completely by greasing the front driveshaft U-Joints as well. You will find the front driveshaft U-Joints where the driveshaft and transmission connect. Go ahead and repeat the same greasing process as you did on the rear U-Joints. After you finish, wipe out any excess grease which came out during the greasing process using a clean rug.

Spicer Universal Joint Lubrication Path  YouTube Video

Frequently Asked Questions (FAQs)

Q. How Often Do You Grease U-Joints?

It is advisable to grease U-Joints during periodic maintenance. Some other vehicles recommend greasing after every 40,000-50,000 miles if the car is working in a normal environment or less when driving in a harsh environment. It is also prudent to grease the U-Joints and to steer every time you get in deep mud or water and every time you do car maintenance.

Q. What Kind of Grease Do You Use on U-Joints?

The best type of grease to use on U-Joints is MOLY grease. This grease is certified for this purpose. You can also use lithium-based EP NLGI 2 Grease, which is of high quality. This grease is also water-resistant and prevents the joints from corrosion and rust.

Q. What Happens If You Do Not Grease U-Joints?

If your car runs on degreased U-Joints, the internal metal parts start grinding together. The surface then gets exposed to the dirt and dust from the outer environment, which will finally lead to U-Joints failure. Greasing your U-Joint helps in extending their expected life use.

Q. Can You Drive With Bad U-Joints?

Yes, you can drive your car with bad U-Joints, but you will never have a satisfying driving experience. There will be an awful vibration during the ride beginning from the center to the back of the vehicle. There will also be a clunking sound when letting off or pressing the accelerator. It is, therefore, better to diagnose the failure and get the U-Joints replaces where need be.

Q. What Are The Signs of a Bad Universal Joint?

There are two major signs that caution you when something is wrong in the universal joint. First, there will be high metal clunking noise when moving forward to going reverse. The other sign is vibrations in the vehicle, especially when moving at high speed.

Final Words:

Here we got to know more about joints and U-Joints in particular, how they work and how to grease them step by step. We have also learned how often to grease U-Joints and the symptoms of the bad ones. One important thing that many people often forget is checking and greasing U-Joints periodically. Greasing universal joints is an essential job to have a safe ride.

Failing to care for and service the U-Joints properly may cause adverse implications. For instance, driving shafts may fall completely when on the road. Vibrations also put additional stress on the transmission’s output shaft and internal parts. This may result in damaging the car’s transmission or other drive train parts, which will cost you a fortune and put your vehicle in danger.


Hi there, I am R. Hasan Tito, a mechanic, and owner of this website. My friend and I created this website to share our knowledge, expertise, and experience with our fellow mechanics' community and car users. I am a specialist and certified automotive mechanic (Both Heavy Commercial and Private Cars). I worked as a Mechanic and Mechanic Supervisor for over fifteen years at Global Rebound Automotive companies - Toyota, TATA, BMW, Nissan, TVs, and Others. Now, I enjoy my new role of leading a team of automotive experts (in their respective fields) and publish new content on a regular basis on my website and social media.

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