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”. Both the inner and the outer joints are covered with a protective boot.
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 and water 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.
Description: An aluminum case containing a torque converter, an arrangement of planetary gears, clutches & bands, servos, a hydraulic system, solenoids, and a valve body. On front wheel drive cars, the transmission and differential are combined into a single housing called a transaxle.
Purpose: An automatic transmission/transaxle changes the engine’s speed and torque in relation to the speed and torque of the drive wheels. This keeps the engine’s output matched as close as possible to varying road speeds and loads. The torque converter, connected to the transmission/transaxle input shaft, connects, multiplies and interrupts the flow of engine torque into the transmission.
Maintenance Tips/Suggestions: Most of today’s automatic transmissions/transaxles do not require any regular adjustments. For best results, have your car’s transmission fluid and filter changed every two years or 40,000 kilometers.
Fact is, the overwhelming majority of transmission failures are heat-related, and automatic transmission fluid breaks down rapidly when subjected to high temperatures. Driving conditions such as trailer towing, quick stops and starts, ascending and descending mountains, and wheel-spinning in slippery conditions are but a few scenarios that can devastate the life of the transmission fluid.
Description: Automatic transmissions/transaxles use a filter on the inlet side of the transmission’s hydraulic pump. Different types of filtering media may be used including a fine mesh screen, paper, or felt for filtering media.
Purpose: A transmission filter prevents harmful contaminants from entering the hydraulic system, where they can increase wear and cause scoring and sticking of hydraulic control valves. Additionally, if a major part fails inside the transmission, the filter may prevent pieces of that part from contributing to a more catastrophic transmission failure. Normally transmission filters trap metal chips from hard parts like gears and bushings and the normal fine material that results from wear of the hydraulic clutch facings and bands.
Maintenance Tips/Suggestions: Your car’s automatic transmission filter and fluid should be changed periodically according to the schedule in your owner’s manual. Although some maintenance schedules may claim that the transmission fluid or filter doesn’t need to be changed for the life of the car, remember that the average driving situation falls into the “severe” maintenance category due to short trips and stop-and-go driving. Some shops offer transmission flushing and filling, which is intended to remove more contaminants than simple draining of the transmission. If you decide to have this service performed, make sure that the transmission pan will be removed in order to change the filter before refilling it with new fluid. If the filter is not replaced, contaminants from the old fluid, along with those dislodged during the flushing process, could impair flow through the filter and lead to transmission problems.
Drive Shaft and Universal 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.
Maintenance Tips/Suggestions: 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. 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.
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.
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.
Description: A differential (also called a Rear End) 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. 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.
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.
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 kilometers. 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.
Gaskets & Sealing
Description: Automatic transmissions/transaxles use an arrangement of internal seals in clutch packs, servos, and accumulators. There are also several external seals.
Purpose: Internal seals prevent leakage in clutch packs, servos and accumulators. These components are responsible for applying or absorbing pressure at various points inside the transmission/transaxle. External seals prevent the leakage of fluid outside the transmission/transaxle case and also prevent dirt from entering into the transmission. The oil pan gasket seals the pan to the transmission/transaxle case.
Maintenance Tips/Suggestions: Symptoms of internal seal leakage may include slipping, rough shifts, loss of some gear ranges, or no vehicle movement in forward or reverse. Symptoms of a leaking external seal or transmission/transaxle oil pan gasket usually can be seen as reddish-brown spots in your driveway or parking place, a burning oil smell from underneath the car, and frequent topping-off of the transmission fluid level.
Description: The clutch disc consists of a metal disc covered with a frictional facing similar to brake shoes or pads. The lining is made of a woven or molded non-organic material that also contains particles of soft metal such as aluminum or brass. This improves the strength of the lining and a series of radial grooves in the lining’s face enhances the grip between the flywheel and the disc. A splined hub in the centre of the disc mates with the transmission’s input shaft, thereby providing a direct mechanical coupling between the two. The clutch disc is located between the flywheel and pressure plate.
Purpose: The clutch disc transmits engine torque directly to the input shaft of the transmission. The clutch disc, when coupled with the pressure plate and flywheel, makes and breaks the flow of power from the engine to the transmission.
Maintenance Tips/Suggestions: Since pressure to the clutch disc is applied and released continuously throughout the course of normal driving, the clutch disc lining will wear over time making it a normal wear item.
Another common clutch problem is clutch slippage. This can be caused by a variety of factors such as a damaged pressure plate, worn, binding or misadjusted linkage, incorrect clutch components, and even normal wear.
Clutch Safety Switch
Description: The clutch safety switch, sometimes called a clutch start or interlock switch, is an electrical switch connected to the engine’s starting circuit.
Purpose: The clutch safety switch prevents the engine’s starter motor from cranking the engine unless the driver applies the clutch pedal. This eliminates the chance of cranking the engine with the transmission in gear, which could cause sudden vehicle movement, especially if the engine starts. In some cases, the clutch safety switch also serves a secondary purpose — it disables the cruise control if the driver applies the clutch with the cruise control engaged.
Maintenance Tips/Suggestions: Not all cars are equipped with a clutch safety switch, so check your owner’s manual for mention of this safety device. Problems with the clutch safety switch may include a no-start condition, starting with the clutch released and the transmission in gear, and inoperative cruise control.
Description: The flywheel mounts to the engine’s crankshaft and transmits engine torque to the clutch assembly. The flywheel, when coupled with the clutch disc and pressure plate makes and breaks the flow of power from the engine to the transmission.
Purpose: The flywheel provides a mounting location for the clutch assembly. When the clutch is applied, the flywheel transfers engine torque to the clutch disc. Because of its weight, the flywheel helps to smooth engine operation. The flywheel also has a large ring gear at its outer edge, which engages with a pinion gear on the starter motor during engine cranking.
Maintenance Tips/Suggestions: Clutch chatter is a common symptom that may indicate a poor flywheel surface or a worn clutch, but this symptom could also be caused by oil leaking from the engine onto the clutch assembly, damaged release levers, a sprung clutch disc hub, or improper alignment between the engine and transmission. The face of the flywheel, the area that contacts the clutch disc, is subject to “heat checking” which occurs during excessive heat build-up between the clutch disc and flywheel. This is the result of excessive slippage between the two. In many cases, the flywheel can be resurfaced during a clutch replacement.
Description: The pressure plate contains a clutch plate, springs, cover and release fingers. This sub-assembly bolts to the flywheel, with the clutch disc sandwiched in between. Although there are two types of pressure plates, the spring-type and the diaphragm-type, the latter is used most often.
Purpose: The pressure plate, as its name implies, applies pressure to the clutch disc for the transfer of torque to the transmission. The pressure plate, when coupled with the clutch disc and flywheel, makes and breaks the flow of power from the engine to the transmission.
Maintenance Tips/Suggestions: To get to the heart of your car’s clutch problem, have a professional technician road test your car to confirm the symptoms you’re experiencing. It is the best first step of a proper diagnosis.
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 to the affected wheel.
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.
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.
Continuously Variable Transmission
Description: A Continuously Variable Transmission (CVT) uses an arrangement of pulleys and bands to achieve an unlimited variation between the highest and lowest ratios. Unlike conventional automotive transmissions, CVTs do not employ a graduating arrangement of fixed gear ratios to deliver power transmission. CVTs have seen spotty vehicle applications over the years, but have staged a recent comeback due to improving and emerging technologies.
Purpose: CVTs help the engine stay closer to its most efficient operating range, which can help both performance and fuel economy. CVTs may also offer manufacturers different economies of scale for transmission manufacturing.
Maintenance Tips/Suggestions: CVTs require a different maintenance regimen than conventional manual or automatic transmissions. Refer to your car’s owner’s manual for specific recommendations for CVT maintenance.