Car Care Drive Train


  1. Bearings & Seals
  2. Drive Shaft & U-Joints
  3. CV Shaft, Boots & Joints
  4. Transfer Case
  5. Traction Control
  6. Differential
  7. Axle

Bearings & Seals

Description: Bearings are the load-carriers inside virtually every part of the drivetrain. Bearings have numerous types of designs for different applications. Typical automotive designs include: tapered roller, straight roller, flat, ball, and needle bearings. Bearings usually receive lubrication from the main component where they're located, but there are some bearings that need cleaning and lubrication as regular maintenance. Today's cars and light trucks also use "lubed-for-life" bearings for some applications that do not need periodic maintenance for the life of the bearing. Long bearing life is only possible if dirt is prevented from entering a bearing; that's where seals come in. Seals have many different applications: front wheel bearing seals, axle shaft seals, pinion gear seals, transmission extension housing seals, and so on. Seals may have a single or double lip, which is the sealing surface of the seal. This is usually made out of a synthetic material and enclosed within a metal ring.

Purpose: Bearings are used to support loads and reduce friction of rotating parts in transmissions/transaxles, transfer cases, universal joints, front and rear drive axles, axle hubs, and wheel hubs among others. Seals are used most often to keep grease, oils, and other lubricants from leaking out, but also to prevent dirt from getting in.

Maintenance Tips/Suggestions: Check your car's maintenance schedule for recommended bearing service intervals. Typically, the only bearings requiring regular service are wheel bearings. Although many cars have non-serviceable, lubed-for- life wheel bearings in front, there may still be serviceable bearings in the rear. Most SUVs and pickups still need regular front wheel bearing maintenance. Have the bearings cleaned, inspected and repacked with fresh lubricant every two years or 40,000 kilometres. If the wheel bearings are exposed to any underwater conditions, even for a short period, the bearings need to be serviced more frequently.

The wheel seals should also be replaced every time the bearings are serviced. Symptoms of a faulty wheel bearing include a growling or metal-to-metal noise from one of the wheels while the vehicle is moving, wandering steering, or a seized wheel. If you suspect a bad wheel bearing on your car, have it checked out by a qualified service professional as soon as possible.

Drive Shaft & U-Joints

Description: A drive shaft and universal joints (U-joints) connect the transmission to the rear drive axle on most rear-wheel-drive vehicles. Many four-wheel-drive vehicles also use drive shafts and universal joints, with one drive shaft between the transfer case and rear drive axle and a second drive shaft between the transfer case and the front drive axle. The drive shaft is sometimes called a propeller shaft.

Purpose: The drive shaft and U-joints provide a means of transferring engine torque to drive axles. The universal joints allow the drive shaft to move up and down, to allow for suspension travel. Some drive shafts also have a slip joint that allows the drive shaft to make minor length changes as the vehicle suspension height changes.

Maintenance Tips/Suggestions: Check your vehicle's owner’s manual for maintenance intervals on the drive shaft and U-joints. Many vehicles have U-joints that are "lubed-for life" from the factory and do not require periodic lubrication. Even if the U-joints can't be lubricated, they should at least be inspected at every oil change. Also, SUVs and pick-ups often have lubrication fittings on drive shaft slip joints. Ask for these to be lubricated when bringing your vehicle in for service. Replacement U-joints often come with lubrication fittings, so if the U-joints are replaced on your vehicle, make sure they're lubricated at every oil change.

Symptoms of a bad universal joint include a repeating squeaking sound when accelerating from a stop, a heavy clunking noise when shifting from drive to reverse or visa versa, or a shuddering sensation when accelerating or driving. If your vehicle shows any of these symptoms, have it inspected as soon as possible by a qualified service technician. Neglecting the warning signs of a bad U-joint could cause the drive shaft to separate from the vehicle, making repairs more expensive and possibly damaging the vehicle.

CV Shaft, Boots & Joints

Description: The constant-velocity (CV) shaft, boot and joints are all part of the same assembly and are used on front-wheel-drive and many four-wheel-drive vehicles. One shaft assembly is used per side, and is sometimes dubbed a "half-shaft". The transmission's output shaft connects to the inner CV joint. The inner joint has the ability to slide in and out and therefore make minor changes in the overall length of the shaft assembly. This is important to allow for changes in suspension travel and ride height.

From there, the main portion of the axle shaft connects the outer CV joint. Both the inner and the outer joints are covered with a protective boot. The outer CV joint has the inherent ability to provide even torque transfer, even while the wheels are turned sharply. The CV joint then connects to a stub shaft that joins with the wheel hub and bearing assembly. Older front-wheel-drive vehicles used to use unequal length shafts, which led to a driving characteristic known as "torque steer"-pulling to one side while accelerating. Today, most cars have equal length shafts on both sides, which neutralizes the effects of torque steer.

Purpose: CV axle shaft assemblies fulfill the demanding role of having to supply torque to the wheels while turning and while the suspension is moving up and down.

Maintenance Tips/Suggestions: Have your car's CV boots inspected at every oil change. CV boots can be easily damaged from rocks, sticks, ice and just normal wear. When a CV boot tears or cracks, the lubricant packed inside is free to move out of the CV joint and dirt is now allowed into the joint. Unless the damage to the boot is discovered quickly, it's likely that the joint will also need to be replaced along with the boot. A replacement axle may be the wisest choice, depending on cost. The symptom of a bad outer CV joint is usually a clicking noise while turning. A shudder, vibration or clunking sound when accelerating or decelerating usually means trouble in the inner CV joint. Don't ignore the warning signs of a bad CV joint; you could lose steering or be stranded. Take your car to a qualified service professional as soon as possible to have the source of the drive train problem pinpointed.

Transfer Case

Description: The transfer case attaches to the transmission and connects to both the front and rear drives axles of a four-wheel-drive vehicle. A transfer case usually has several different operating modes, controlled by the driver.

Purpose: The transfer case routes torque from the transmission to both the front and rear axles. Depending on the design, the transfer case may provide equal amounts of torque to the front and rear axles, or the transfer case may proportion torque to the front and rear axles based on the amount of traction or slippage at the wheels. Transfer cases usually have different modes and ranges of operation. Check your vehicle's owner's manual to acquaint yourself with the details of different driving modes.

Maintenance Tips/Suggestions: The transfer case should be checked at every oil change to ensure that it has enough lubricant. It's also a good idea to check the owner's manual for your vehicle to find out the maintenance interval for the transfer case. Many transfer cases require periodic changes of oil or fluid to maintain peak performance; use the lubricant specified by the manufacturer. Although transfer cases are usually trouble-free, they can develop problems over time. Common problems may include: no four-wheel-drive operation, four-wheel-drive operation only in some modes, or the inability to switch modes. These problems do not necessarily mean that the transfer case itself is at fault. The problem may lie in the transfer case engagement controls, as many of today's vehicles use electric or vacuum controls to carry out driver's commands. If your vehicle shows signs of a transfer case problem, have the system evaluated by a qualified service technician.

Traction Control

Description: Traction control is a system that integrates with the engine control system, brakes, and antilock brakes to control wheel slippage under acceleration.

Purpose: By working with other vehicle systems, traction control manages these systems to limit and redirect torque output to the drive wheels of the vehicle. The end result is optimum torque output at the wheels for virtually any driving condition. When the traction control system senses slippage at a given drive wheel, it may limit engine output through various control strategies and apply the brakes.

Maintenance Tips/Suggestions: Traction control is more of an integrated strategy than a system of its own; by itself, traction control requires no dedicated maintenance. To ensure proper traction control operation, regular maintenance of related systems is a must. This means regular brake inspections, replacing worn brake parts and flushing/refilling of the brake hydraulic system per the manufacturer's recommendations. Regular engine performance checks also help to ensure proper traction control operation. Faults in the engine's control system can affect traction control, so have any problems corrected as soon as possible.

Most traction control systems use a warning light on the dash to alert the driver of a system fault. This light should come on momentarily (bulb check) when the ignition is first turned on, and then go out. If the light doesn't come on when the ignition is first turned on, stays on or comes on while driving, the traction control system needs to be checked for faults. Contact a professional service technician to have the system diagnosed.

On some cars, there may be wires encircling the mini-spare tire in the trunk, which can't be removed unless you separate the connector deactivating the traction control functions. This is necessary when the spare is installed because of the difference in tire size. Unplugging the connector turns the system off. A light on the dash may read, TRACTION DISABLED FOR MINI-SPARE. Keep in mind that the spare tire may have an effect on traction control operation.

Differential

Description: A differential consists of a ring gear, pinion gear, side gears, spider gears, and bearings. All of these components may be encased in an axle housing or they may be located inside an automatic or manual transmission/transaxle. Positive-lock differentials, which may go by names such as Positraction or Traction-lock, have the ability to shift torque from the wheel that is slipping to the wheel that is not. Four-wheel-drive vehicles have a separate differential for each pair of wheels.

Purpose: The differential transfers torque from the drive shaft or transmission output to the differential's drive axles. The spider gears and side gears allow the axles to turn at different rates, which is necessary when the car makes a turn. The outer wheel must turn faster than the inner wheel, creating a speed differential (which is how it got its name).

Maintenance Tips/Suggestions: Have the axle lube level checked with every oil change. On most front-wheel-drive vehicles, the differential is part of the manual or automatic transaxle, and therefore does not require a separate differential lube check. If you have a rear-wheel-drive or four-wheel-drive vehicle, check the owner's manual to find out the recommended interval for differential lube changes.

Positive-lock differentials may require a different lube or a lube additive. Many manufacturers claim their differentials to be “lubed for life”, unless it has been submerged in water. If you have a pickup or SUV, this may happen quite often, especially if you pull a boat. If this is the case, have the axle lube changed at least once a year.

In cold climates, you may want to consider changing the standard axle lube to a synthetic type. Synthetic lubes flow easier in cold weather, improving lubrication. With a 4/4, this is doubly the case because of the two axles. Always use a lubricant that meets or exceeds the manufacturer's lube specifications. When cared for properly, differentials provide many thousands of miles of trouble-free operation. When a differential problem does occur, symptoms may include: a high-pitch sound when accelerating or decelerating, clunking when accelerating or when shifting between reverse and drive, or a howling sound. Differential problems should be checked out as soon as possible by a qualified service professional.

Axle

Description: An axle is a load-bearing assembly that connects two wheels together on opposite sides. There are several types of axles used on cars and light trucks. The most common is the transaxle, which encases an automatic or manual transmission and a differential. Another popular type of axle is the drive axle, sometimes referred to as a live axle, which contains the differential. The least popular type of axle, which is fading quickly from use, is the non-driving straight axle. This axle is basically a straight beam that connects the wheels together, but has no differential. The straight axle was once used commonly at the rear of front-wheel-drive vehicles and on the front of rear-wheel-drive pick-ups. With the growing popularity of independent suspension systems, the straight axle is rapidly becoming obsolete.

Purpose: Since axles vary in complexity, so do their purposes. A simple straight axle helps to support the weight of the vehicle and serves as an attachment point for the wheels. A drive axle does all of this, along with providing the torque transfer capabilities of a differential. A transaxle serves all of the same purposes as a drive axle, but also includes the gear-changing capabilities of a transmission.

Maintenance Tips/Suggestions: Axle maintenance is related to the complexity of the axle. A straight axle requires periodic cleaning and repacking of wheel bearings, usually every two years or 40,000 kilometres. Drive axles should have the axle lube level checked with every oil change. On most front-wheel-drive vehicles, the differential is part of the manual or automatic transaxle, and therefore does not require a separate differential lube check. If you have a rear-wheel-drive or four-wheel-drive vehicle, check the owner's manual to find out the recommended interval for differential lube changes.

Positive-lock differentials may require a different lube or a lube additive. Many manufacturers claim their differentials to be "lubed for life", unless it has been submerged in water. If you have a pickup or SUV, this may happen quite often, especially if you pull a boat. If this is the case, have the axle lube changed at least once a year.

In cold climates, you may want to consider changing the standard axle lube to a synthetic type. Synthetic lubes flow easier in cold weather, improving lubrication. With a 4/4, this is doubly the case because of the two axles. Always use a lubricant that meets or exceeds the manufacturer's lube specifications. When cared for properly, differentials provide many thousands of kilometres of trouble-free operation.

When a differential problem does occur, symptoms may include: a high-pitch sound when accelerating or decelerating, clunking when accelerating or when shifting between reverse and drive, or a howling sound. Differential problems should be checked out as soon as possible by a qualified service professional.