Rear output shaft

Types of Rear Output Shaft

The rear output shaft is a vital component of many vehicles, especially four-wheel drive (4WD) and all-wheel drive (AWD) systems. Its primary function is to transfer power from the transfer case to the drive axles, enabling the vehicle to move. Depending on the vehicle design and drivetrain layout, the rear output shaft can come in different types.

• Splined Shafts

  These are the most common types of rear output shafts found in many 4WD and AWD vehicles. They feature a series of ridges and grooves (splines) along the length of the shaft. The splines engage with matching grooves in the yoke or flange attached to the drive axle or universal joint. This design allows for torque transfer while accommodating slight misalignments and axial movements between the transfer case and the drive components. Depending on the vehicle's power output and intended use, splined shafts come in various sizes and spline counts.

• Keyed Shafts

  In some older or less performance-oriented vehicles, the rear output shaft may use a keyed design. Keyed shafts feature a single, wide flat on one side of the shaft, along with a matching keyway slot in the transfer case and yoke or flange. A metal key fits into the keyway slots, locking the yoke or flange onto the shaft. While simple and effective for low-torque applications, keyed shafts are less suitable for high-performance use. The keyed design limits torque transfer capacity and can be prone to slippage or failure under high-stress conditions.

• Round Pin or Pinned Shafts

  Occasionally, some heavy-duty trucks and off-road vehicles utilize round pin or pinned shaft designs for the rear output. These shafts feature multiple round pins or small-diameter rods running through the shaft and transfer case, yoke, or flange. The pins engage with corresponding holes or grooves in the mating components, providing a more robust connection for extreme torque transfer applications. Pinned shafts can handle higher torque loads than splined or keyed designs. As such, they are suitable for heavy trucks or off-road vehicles that require reliable power delivery to drive the wheels in extreme conditions.

Specification & Maintenance of Rear Output Shaft

When it comes to the specifications of the rear output shaft, it is worth noting that they vary from one model to another. The differences arise depending on the size, design, and material. Nevertheless, here are some common specifications to be on the lookout for:

• Length and Diameter

  The length and diameter of a rear driveshaft are vital to its function. Generally, the diameter has to be proportional to the power the shaft transmits. An undersized shaft may not be able to handle the power. On the other hand, an oversized shaft may be out of balance and vibrate. This could damage the bearings and other parts of the driveshaft. The length of the rear driveshaft is equally important. A shaft that is too short will not be able to transfer the power effectively. One that is too long may be too flexible and not transmit the power properly.

• Universal Joints

  Universal joints (U-joints) are vital components of the rear output shaft. They connect the shaft to the differential and the transfer case. U-joints allow the driveshaft to rotate smoothly, even when the axles are not perfectly aligned. This is important, especially when turning corners or driving on uneven surfaces. The size and type of U-joints used on the rear output shaft will depend on the make and model of the vehicle. For instance, heavy-duty trucks and off-road vehicles require larger and more durable U-joints. This is because these vehicles experience more stress and strain when driving.

• Material

  The material of the rear output shaft is also a key specification. Output shafts are commonly made from hardened steel or other alloys. These materials were chosen for their strength and durability. Remember, the output shaft has to withstand high pressure and stress. This is especially true when accelerating or towing heavy loads. The output shaft also has to endure high temperatures, such as when driving in hot conditions or on hilly terrain.

• Gear Ratio

  The gear ratio of the rear output shaft is also an important specification. The gear ratio affects the power and speed delivered to the rear wheels. A lower gear ratio (numerically higher) provides more torque and pulling power but less speed. This is ideal for off-road or towing applications. On the other hand, a higher gear ratio (numerically lower) offers more speed and less torque. This is beneficial for highway driving or when carrying lighter loads.

It is crucial to maintain the rear output shaft properly. This will not only increase its functionality but also its durability. Here are some tips for maintaining the rear output shaft:

• Regular Inspection: Carrying out regular inspections on the rear output shaft is important. This is because it helps to identify problems like wear and tear, rust, or damage. Drivers should also check the U-joints, bearings, and other components for signs of wear or damage. Look for issues like play, binding, or noise. The earlier these problems are detected, the easier they are to fix.
• Lubrication: The rear output shaft requires regular lubrication to run smoothly. Use the recommended type and amount of lubricant for the specific vehicle. Remember, the lubricant helps to reduce friction and wear between the moving parts. This is especially important for the U-joints and bearings. Re-lubricate them regularly to ensure a long lifespan.
• Seals and Dust Covers: Seals and dust covers protect the rear output shaft from dirt, dust, and moisture. This helps to prevent contamination and damage to the shaft and its components. Check the seals and dust covers regularly for signs of wear or damage. Replace them immediately if they are worn out or damaged.
• Alignment and Balancing: Proper alignment and balancing of the rear output shaft are crucial for its optimal performance. An unbalanced or misaligned shaft can cause vibrations, which can lead to damage to the shaft and its components. Use the appropriate tools and equipment to check the alignment and balance of the rear output shaft. Adjust it accordingly to ensure a smooth and efficient operation.

How to Choose Rear Output Shaft

Choosing the right rear output shaft can greatly improve the durability and performance of a driveshaft in any vehicle. Here are a few things to consider when choosing a proper rear output shaft.

• Understand the Vehicle:

  This involves understanding the make, model, and year of the car. This is important because different vehicles have different output shaft sizes and styles.

• Consider the Driving Condition:

  The driving condition is very important when selecting a rear output shaft. For vehicles used in off-road conditions, a heavy-duty output shaft that can withstand rugged terrain is required.

• Future Upgrades:

  When selecting a proper rear output shaft, future upgrades should be considered. A well-chosen rear output shaft can support future upgrades.

• Budget:

  Budget is an important factor to consider when selecting a proper rear output shaft. High-quality output shafts are expensive but offer great value.

How to DIY and replace rear output shaft

When DIYing the rear output shaft seal replacement, a mechanic will need to gather some tools and prepare for the task. The tools needed are an appropriate socket, hammer, seal driver or a piece of pipe, flat-blade screwdriver, jack and jack stands, torque wrench, new rear output shaft seal, and gear lubricant.

Follow the steps below to replace the rear output shaft seal successfully.

• Vehicle preparation

  First, the mechanic will need to park the vehicle on a level ground. Then, engage the parking brake and place wheel chocks on the front wheels. After that, they will loosen the lug nuts on the rear wheels, raise the vehicle using a jack, and support it on jack stands. Once stable, they will remove the wheel chocks and open the hood to remove the cap from the filler neck of the transfer case.

• Drain fluid

  Next, the mechanic will place a drain pan under the transfer case and remove the drain plug to drain the fluid. They will allow the fluid to completely drain and then install the drain plug securely.

• Remove the drive shaft

  The mechanic will need to remove the bolts securing the rear drive shaft. After that, they will slide the drive shaft yoke off the output shaft and set it aside.

• Remove the old seal

  Once the drive shaft is out of the way, the mechanic will carefully pry out the old seal using a flat-blade screwdriver. They will be careful not to damage the surrounding housing while removing the seal.

• Install the new seal

  Before installing the new seal, they will apply a thin layer of grease to the lip of the seal. Then, they will position the new seal over the opening and gently tap it into place using a seal driver or a piece of pipe. The seal should sit flush with the housing.

• Reassemble components

  After the seal is securely in place, the mechanic will reattach the rear drive shaft to the output shaft using the previously removed bolts. They will also lower the vehicle, remove the jack stands, and raise it again to tighten the bolts securely while the vehicle is on the ground.

• Fluid replacement

  Once the vehicle is secure, they will remove the rear wheels and wheel chocks, then lower it to the wheel servicing structure. They will then remove the wheel chocks, open the hood, and add the recommended fluid into the transfer case through the filler opening until it starts to overflow. Finally, they will replace the filler cap and wheel chocks.

Q and A

Q1. What is the rear output shaft?

A1. The rear output shaft is a part of the transfer case in four-wheel-drive and all-wheel-drive vehicles. It takes power from the transfer case and sends it to the driveline, which has components like the rear drive axles and the wheel hub assembly, to spin the rear wheels. The rear output shaft is also called the rear output yoke or the rear output flange.

Q2. What are the signs of a worn-out rear output shaft?

A2. The first sign is a noise that comes from the transfer case when users accelerate. There will be a grinding or rattling sound. The second sign is vibrations felt in the vehicle when users drive. The third sign is a fluid leak that users can notice when they inspect the transfer case. The final sign is difficulty in shifting gears, especially when moving the gear lever to 4WD.

Q3. How do people maintain the rear output shaft?

A3. Users should maintain the rear output shaft by ensuring the transfer case is in good condition. They should change the transfer case fluid as per the owner's manual recommendations. Also, when they notice any of the signs mentioned above, they should take the vehicle to a professional mechanic. The mechanic will inspect the transfer case and output shaft to determine whether they need a repair or replacement.

Q4. What is the difference between a fixed and a slip output shaft?

A4. A fixed output shaft has a u-joint at the end that connects to the drive shaft. It doesn't allow for length variation. On the other hand, a slip output shaft has a slip yoke at the end. The slip yoke connects to the drive shaft and allows for length adjustment. The slip output shaft is more common in modern 4WD and AWD vehicles.

Q5. Can a rear output shaft be used on any vehicle?

A5. No, the output shaft is designed for a specific transfer case and vehicle configuration. Users must ensure the output shaft matches their transfer case model and specs. Otherwise, they will experience fitment issues and possible drivetrain damage.