Transaxles

A transaxle is a transmission and differential combination in a single assembly. Transaxles are used in front-wheel drive vehicles. A transaxle allows the wheels next to the engine to propel the vehicle. Short drive axles are used to connect the transaxle output to the hubs and drive wheels. Vehicle manufacturers claim that a transaxle and front-wheel drive vehicle has several advantages over a vehicle with rear-wheel drive. A few of these advantages are the following:

• Improved efficiency and reduced drive train weight

• Improved traction on slippery surfaces because of increased weight on the drive wheels

• Increased passenger compartment space (no hump in floorboard for rear drive shaft)

• Less unsprung weight (weight that must move with suspension action), thereby providing a smoother ride

• Quieter operation since engine and drive train noise is centrally located in the engine compartment

• Improved safety because of the increased mass in front of the passengers

Most transaxles are designed so that the engine can be transverse (sideways) mounted in the engine compartment. The transaxle bolts to the rear of the engine. This produces a very compact unit. Engine torque enters the transaxle transmission. The transmission transfers power to the differential. Then the differential turns the drive axles that rotate the front wheels. Both manual and automatic transaxles are available. Manual transaxle uses a friction clutch and a standard transmission-type gearbox. An automatic transaxle uses a torque converter and a hydraulic system to control gear engagement.

Manual Transaxles

A manual transaxle uses a standard clutch and transmission (Figure 10-28). A footoperated clutch engages and disengages the engine and transaxle. A hand-operated shift lever allows the operator to charge gear ratios. The basic parts relating to a manual transaxle are the following:

• Transaxle input shaft—main shaft splined to the clutch disc, turns the gear in the transaxle.

• Transaxle input gears—either freewheeling or fixed gears on the input shaft, mesh with the output gears.

• Transaxle output gears—either fixed or freewheeling gears driven by the input gears.

• Transaxle output shaft—transfers torque to the ring gear, pinion gears, and differential.

• Transaxle synchronizers—splined hub assemblies that can lock freewheeling gears to their shafts for engagement.

• Transaxle differential—transfers gearbox torque to the driving axle and allows the axles to turn at different speeds.

• Transaxle case—aluminium housing that encloses and supports parts of the transaxle.

The manual transaxle can be broken up into two separate units—a manual transaxle transmission and a transaxle differential. A manual transaxle transmission provides several (usually four or five) forward gears and reverse. You will find that the names of shafts, gears, and other parts in the transaxle vary, depending on the location and function of the components. For example, the input shaft may also be called the main shaft, and the output shaft is called the pinion shaft because it drives the ring and pinion gear in the differential. The output, or pinion, shaft has a gear or sprocket for driving the differential ring gear.

The clutch used on the manual transaxle transmission is almost identical to the manual transmission clutch for rear-wheel drive vehicles. It uses a friction disc and springloaded pressure plate bolted to the flywheel. Some transaxles use a conventional clutch release mechanism (release bearing and fork); others use a long pushrod passing through the input shaft. The transaxle differential, like a rear axle differential, transfers power to the axles and wheels while allowing one wheel to turn at a different speed than the other. A small pinion gear on the gearbox output shaft or countershaft turns the differential ring gear. The ring gear is fastened to the differential case. The case holds the spider gears (pinion gears and axle side gears) and a pinion shaft. The axle shafts are splined to the differential side gears.