Manual Transmissions and Transaxles 

Transmission Versus Transaxle 

•  Rear-Wheel-Drive vehicles are propelled by the rear wheels and normally use a transmission .

1. • Transmission gearing is located within an aluminum or iron casting called the transmission case assembly.  The transmission case is normally located in the front of the vehicle. 
   • A drive shaft links the output shaft of the transmission with the differential and drive axles located in separate housing at the rear of the vehicle.
   • The differential splits the driveline power and redirects it to the two rear drive axles, which then pass it on the wheels.

• Front-wheel-drive vehicles are propelled by the front wheels.
  
• • For this reason, they must use a drive design different from that of a RWD vehicle.
  • The transaxle is the special power transfer unit commonly used on FWD vehicles.
  • A transaxle combines the transmission gearing, differential, and drive axle connection into a single case aluminum housing located in front of the vehicle.
  • One major advantage is the good traction on slippery roads due to the weight of the drivetrain components being directly over the driving axles of the vehicle. 
  • It is also more compact and lighter than the transmission of a RWD vehicle.
  • Transverse engine and transaxle configurations also allow for lower hood lines, thereby improving the vehicle's aerodynamics.

• Four-wheel-drive vehicles typically use a transmission and transfer case.
• • The transfer case mounts ton the side or back of the transmission.
  • A chain or gear drive inside the transfer case receives power from the transmission and transfers it to town separate drive shafts.
  • One drive shaft connects to a differential on the front drive axle.
  • The other drive shaft connects to a differential on the rear drive axle.

• All-Wheel-Drive (AWD), all four wheels are driven.  These vehicles are not designed for off-road use but are to improve poor traction in icy or snowy driving.
   
• • Control is improved by transferring engine power to the wheel with the most traction.  Most AWD systems have a center differential to split the power between the front and rear axles.  The transfer case has the differential within the transfer case.  Four-wheel-drive transfer cases do not have this differential. 
  • When there is a center differential, if one wheel is lifted free of the ground, it is possible for all of the torque to go to that wheel.  This means no power goes to the other wheels. 
  • A lockout for the center differential must be included in these types. 

 Transmission Designs

•  All automotive transmissions/ transmissions/transaxles are equipped with varied number of forward speed gears, a neutral gear and on reverse speed.
  
• • Transmissions can be divided into groupings based on the number of forward speed gears they have.
  • • In the past, the most commonly used transmission was a three-speed; four-speeds were only found in trucks and high-performance cars.
  • The growing concern for improved gas mileage led to smaller engines with four-speed transmissions.
  • • The additional gear allowed the smaller to perform better by matching the engine's torque curve with vehicle speeds and loads.
  • Five-speed transmission and transaxles are now the commonly used units. 
  • • Most late-model five speed units incorporate a fifth gear in their main assemblies.
  • This is true also of six-speed transmissions and transaxles.
  • • The fifth and sixth gears are included in the main assembly and typically provide two overdrive gears.
    • The addition of the two overdrive gears allows the manufactures to use lower final drive gears for acceleration.
    • The fifth and sixth gears reduce the overall gear ratio and allow for slower engine speeds during highway operation.

Transmission Features

• Although they operate in a similar fashion, the layout, components, and terminology used in transmissions and transaxles are not exactly the same.
  
• • A transmission has three specific shafts: the input shaft, the countershaft, and the mainshaft or output shaft.
  • • The countershaft is several gears machined out of a single piece of steel.
    • The main gears on the main shaft or output shaft transfer rotation from the countergears to the output shaft.

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