Out of sight is out of mind. That’s kind of how driveshafts are thought of unless you’re squeezing out every bit of horsepower and torque (or if something goes wrong). And while engines and transmissions get all the attention, it’s the driveshaft that effectively transfers all that power to where it needs to go. Perhaps we’re a bit biased, but the driveshaft is the unsung hero every time you get behind the wheel. But nothing lasts forever, and understanding driveshafts basics and how to spot related problems is a smart move for any car owner.
So, whether you’re still running with a stock shaft or using an aftermarket setup, let’s dive in.
What Does a Driveshaft Do?
Let’s get one thing out of the way; a driveshaft is only applicable for rear-wheel drive and all-wheel/four-wheel-drive vehicles. Front-wheel-drive cars (and rear-engine ones, for that matter) use a transaxle (which combines the differential and transmission into an integrated unit); there’s no driveshaft involved in these applications.
So, for RWD/AWD/4WD vehicles, a driveshaft transfers the power from the transmission to the drive wheels. Although it may seem just a tube of steel, aluminum, or carbon fiber, the shaft is a highly engineered component designed to relay power with each rotation efficiently. At the same time, a driveshaft must operate within both normal and extreme operating conditions. Things like chassis flex and higher RPMs directly affect how a driveshaft performs.
Also, keep in mind that each set of drive wheels will have its own driveshaft. In the case of the rear-wheel-drive car, the shaft will connect the rear differential to the transmission. In an AWD/4WD setup, a smaller driveshaft will join the front wheels to the front differential.
Driveshaft Basics: Single-Piece Vs. Two-Pieces
As the name implies, a single-piece driveshaft relies on a singular tube to transfer power from the transmission to the axle. Setups can include using a yoke that moderately slides across the splines of the transmission output shaft. This configuration allows the shaft to adapt and operate smoothly and optimally.
Along with the driveshaft and yoke are the universal joints (U-joints) that connect the shaft to the differential. U-joints accommodate the different angles of a transmission and driveshaft and allow the rotating shaft to pivot as needed. Compared to a two-piece configuration, a single-piece shaft requires less maintenance and is less prone to problems (due to fewer parts).
A two-piece driveshaft skips the slip yoke at the transmission output shaft in favor of a u-joint connection. Likewise, a u-joint is used at the axle end of the driveline. But unlike a one-piece shaft, a two-piece arrangement handles flex where the two pieces meet in the middle. Outside of applications requiring this type of driveshaft (such as what’s mandated by a manufacturer or in a long-wheelbase car), a two-piece shaft usually has a smaller diameter which can be ideal for tight spaces underneath the vehicle.
Troubleshooting Driveshaft Problems
While car problems seldom involve the driveshaft, it’s wise to understand the symptoms that can indicate troubles with this crucial component. Short of an impact that damages the shaft, most failures result from wear and tear that occurs over time. You may also come across corrosion, so get in the habit of inspecting the underside of your car to get ahead of any problems.
“Clunking” Noises
A clunking or other unusual noise coming from the driveline can be a red flag that a U-joint has seen better days. And the truth is that a U-joint is more likely to fail before the actual shaft does. This makes sense as the bearings inside the U-joints wear down over time. Inspect the U-joints at every oil change and if one needs replacement, assume they all do (as applicable).
Vibrations
Notice of a shuddering or shaking from the driveline is a classic indicator of a driveshaft problem. Be on the alert especially if this happens when accelerating from a low-speed or stopped position. It could be caused by something as simple as a few bolts that need tightening or a shaft that’s out of balance. Or, those “pesky” U-joints could be to blame. Regardless, consider vibrations to be a clue that you should check out the problem. Ignoring an out-of-balance shaft, for example, can lead to reduced performance and mileage, and eventual component failure.
Turning Troubles
While turning difficulties is a common symptom of a suspension or power steering problem, don’t ignore that a bad driveshaft could be to blame. Pay attention to how the car handles during turning and especially when parking..
Ready To Talk Driveshafts?
Let the experts at PST help with your driveshaft needs. Whether you’re trying to get back on the road or looking to hit the track, our experts can engineer the perfect solution for your car. Give us a call at 727-442-1711 to get started.