Driveshaft

• A driveshaft is a metal rod with splined components connecting the transmission and the differential. It serves as the spine on your car which transmits torque to the axles.
• Types of driveshaft include single-piece (flanged) driveshafts and two-piece and three-piece driveshafts.
• Signs that you may be having a failing driveshaft include difficulty in turning the wheel, vibration, audible squeaking noise and vehicle shake during acceleration.
• Driveshafts are important to maintain optimum drivability of the car and to avoid breaking the transmission. Driveshafts are also essential for a comfortable and worry-free drive.
• To find a good replacement driveshaft, consider power and load; length and diameter; and material.
• Price for an individual part usually ranges from $150 to $1400.
• Replacing a faulty driveshaft is easy with the right tools and appropriate know-how.

Have you ever wondered how the wheels on a rear-wheel or all-wheel drive car spin despite being far from the engine and transmission? Simple; there’s a long rod that connects the transmission to the rear differential. This rod is known as the driveshaft or propeller shaft, which incorporates a splined slip joint and sliding yoke that transmits torque to the rear wheels. Basically, the engine’s pistons deliver power to a set of gears inside the transmission. The gears then turn the splined slip joint, which turns the pinion inside the rear differential, causing the axles to rotate.

The driveshaft, like the transmission assembly, is hidden from plain sight but can be located underneath the hump in the rear passenger floor. It serves as the spine of your car, and similar to the spine's function which is to transmit neurons from the brain, the propeller shaft delivers the torque from the transmission to the rear axle of your car. It runs along the center of your car from the transmission hump all the way to the pinion of the rear differential. Be informed that front-wheel drive cars don’t feature driveshafts. Instead, they feature a transaxle, which is a combination of the transmission and front differential.

Driveshafts vary from one vehicle to the other due to factors like vehicle length, drivetrain layout, and transmission design. Considering these  factors, there are two main types of driveshaft; the single-piece and multiple-piece driveshafts.

Single-piece (flanged) driveshafts are used in small vehicles of which the distance between the engine and axles are short. They are also utilized in mid-engine, rear-wheel drive (MR) and four-wheel-drive (4WD) vehicles.

Two-piece or three-piece driveshafts, on the other hand, are used in long vehicles of which the engine and axles are far from one another. This type of propeller shaft is also used in front engine, front-wheel drive (FF) and 4WD vehicles. The divisions of the shaft assembly allow it to absorb vibrations and bending due to extreme rear axle and suspension movements.

Remember that the car driveshaft plays an important role in driving the wheels from a stationary position. It also contributes to your car’s overall driving comfort because a faulty propeller shaft can result in minor and major issues on the road. The symptoms vary from audible sounds to perceivable inconsistencies, all of which are not to be ignored. If you experience these signs while driving, consult your mechanic as soon as possible.

Difficulty in turning the wheel

A bent or damaged driveshaft can restrict your wheels from turning properly, which then results to difficulty in maneuvering the car on curves. This sign should be easy to tell due to the increased resistance from the tire when steering the car. Wheels that won’t properly turn cause inconveniences both during slow and high-speed drives.

Vibration

Vibrations while driving is a vague symptom because it could be anything from your engine to wheel alignment. Be more concerned when the vibration persists even when your car is stationary. Vibration during idle or drive could be due to a badly-shaped driveshaft, literally. Driveshafts, especially the one-piece type, can bend as a result of extreme suspension and axle movements. The bending will make the rotation of internal parts difficult, causing the vibration even when your car’s at rest.

Audible squeaking noise

Part of the signs of a damaged shaft is unusual noises, even more so that it has rotating and moving parts. Squeaks during accelerations that tames down at higher speeds is a sign of the driveshaft’s badly damaged or dry coupling connection known as the U-joint. This squeaking noise can also be heard in a form of clunking, rattling, and scraping. . If this happens to you, don’t risk ignoring it; drive to your mechanic right away, as it could lead to more serious problem in your drivetrain.

Vehicle shake during acceleration

Aside from unusual noises, shaking during acceleration could be a sign of a loose U-joint. . A malfunctioning U-joint, as well as a worn-out center bearing, are what’s causing the jerkiness whenever you try to step on the pedal from rest or low speed. Although it might feel like a natural vehicle behavior, addressing it sooner can save you from possible major problems that could end up reaching your transmission or engine.

There is a simple explanation on why you need to replace a faulty driveshaft, as well as other parts in your vehicle that you may find failing. Basically, damaged or worn-out parts like the driveshaft affect your vehicle’s drivability, which could eventually result to minor to major inconveniences on the road. The thing is, most drivers tend to just shrug a shoulder and risk it until it’s too late. However, you have to take note that the driveshaft is directly connected to your transmission and everyone knows that a car’s transmission assembly is a little expensive to deal with. So, the moment you start experiencing a problem that you think is caused by the driveshaft, make it a priority to bring your car to the service center.

Keep these considerations in mind when picking a new driveshaft for your car or truck:

Power and Load Balance

A driveshaft's transferring capabilities should be balanced with an engine's power. Remember that with every horsepower increase, there also is the increase in load the driveshaft must carry. Too much power from a powerful engine can twist and destroy the driveshaft. On the other hand, make it too strong for a weak engine and you'll be spending too much on something you and your car does not need.

Length and Diameter

Dimensions of a driveshaft have great effects on its critical speed. Basically, critical speed is the limit a driveshaft has of properly being able to carry an engine's power. Exceed the critical speed and the driveshaft becomes shaky and unstable. Push it more and you'll get it bent and useless. A general rule is that a long and wide driveshaft has a higher critical speed compared to short and thin ones.

Material

A driveshaft is constructed using different materials which also affect its critical speed. Take note of this when picking one for your driving or racing needs.

• OEM: The lowest level of driveshaft capable of handling engines between 350-400HP. This type is not suitable for racing.
• DOM/Chrome-Moly: This steel driveshaft can carry the power range of 1,000-1,300HP. It is quite heavy compared to other types. Chrome-molly driveshafts are tougher variant and can carry the same load as the DOM type.
• Aluminum: Though lightweight, this is common in performance cars because of its capacity to support 900 to 1,000 HP. It can be prone to twisting because it is lighter than steel.
• Carbon Fiber: This is the strongest and most expensive type of driveshaft. With high a high critical speed, carbon fiber can carry an engine with 900 to 1,500 HP.

Driveshafts are sold as an individual piece, assembly, or in sets. Individual OE replacement driveshafts, be it a front drive shaft or a rear drive shaft, are priced around $150 to $1,400 but if you need an assembly, you’re looking at roughly $270 to $1,700. A set of front and rear shafts, on the other hand, are priced somewhere along the $500 to $600 mark. Prices could even go higher depending on the make, quality, and the vehicle of which the product is fitted on.

A driveshaft is responsible for transferring power from the transmission to the axles of the drive wheels. If it is damaged, a lot of power is wasted and lost. Hence, it is important to immediately repair a broken driveshaft to ensure the car runs well.

Difficulty Level: Moderate

Tools Needed:

• Floor jack and jack stands
• Chalk
• Wrench set
• Socket set
• Screwdriver
• Handheld sledgehammer
• Transmission Fluid
• Driveshaft replacement

Step 1: Park your car on a flat surface, put it in neutral gear, and elevate with a floor jack. Secure the car on jack stands to avoid accidentally dropping the car.

Step 2: Go underneath the car and locate the rear yoke of the driveshaft which is connected to the rear axle. Mark the connection of the driveshaft to the axle with chalk for later reference. Wedge a screwdriver in the u-joint gap and remove one of the bolts. To access the other bolts, take off the screwdriver and manually turn the driveshaft. Once other bolts are in reach, wedge the screwdriver again and remove the bolt. Once the last bolt is removed, support and lower the driveshaft and lower it to avoid a sudden drop. In case the driveshaft is stuck, lightly tap it with a small sledgehammer.

Step 3: Repeat step 2 for the front yoke.

Step 4: Once the driveshaft is completely off, prepare the new driveshaft by rubbing transmission fluid on the front yoke to be attached to the transmission. Make sure the splines and joints fit when the front yoke of the driveshaft is inserted. Use your chalk markings as a guide. Secure all bolts removed.

Step 5: For the rear yoke, simply raise it to your chalk marking, fit it to the joint and return all the bolts removed.

Step 6: Lower the car and start the engine. Warm up the car for a few minutes before taking it on a test drive.

The whole process can be done in a little over 1 hour.

Tips:

• Ask for help from another person especially when fitting the joints and spines.
• Use goggles to prevent accidental drippings to the eyes.