Visual: A large, usually metal, housing that contains gears and shafts.
It's located between the engine and the propeller shaft (in rear-wheel
drive vehicles) or integrated with the differential (in front-wheel-drive
vehicles).
Function: Changes the gear ratio between the engine and the wheels,
providing different speeds and torque.
Types: Manual or automatic.
Clutch:
Visual: A round, flat plate housed between the engine's flywheel and
the gearbox. It's usually not visible without disassembly.
Function: Disconnects and reconnects the engine from the
transmission, allowing gear changes.
Visual: A heavy, circular metal disc attached to the rear of the engine's
crankshaft. It's often visible when the clutch housing is removed.
Function: Stores rotational energy, smooths out engine power pulses,
and provides a surface for the clutch to engage.
Propeller Shaft (Driveshaft):
Visual: A long, rotating shaft that connects the gearbox to the
differential (in rear-wheel-drive and four-wheel-drive vehicles). It runs
along the underside of the vehicle.
Function: Transmits power from the gearbox to the rear axle.
Components: Universal joints (U-joints) allow for changes in angle.
Transfer Box (Transfer Case):
Visual: A separate gearbox-like unit found in four-wheel-drive vehicles.
It's located between the main gearbox and the propeller shafts.
Function: Splits engine power between the front and rear axles,
providing four-wheel drive.
Features: May have low-range gears for off-road use.
Differential Unit:
Visual: A housing located in the center of the rear axle (or integrated
with the front axle in front-wheel-drive vehicles).
Function: Allows the wheels on an axle to rotate at different speeds,
which is essential when turning.
Components: Gears, bearings, and a differential carrier.
Types: Open differential, limited-slip differential, locking differential.
Changing transmission oil
Changing transmission oil is a crucial maintenance task that ensures smooth gear
shifts and prolongs the life of your transmission. Here is a general procedure, but
always refer to your vehicle's service manual for specific instructions:
Tools and Materials:
New transmission fluid (correct type and quantity)
Drain pan
Wrenches or sockets (appropriate sizes)
Funnel
Rags or shop towels
Jack and jack stands (or ramps)
Torque wrench (recommended)
New drain plug gasket (if applicable)
Procedure:
Prepare the Vehicle:
Park the vehicle on a level surface.
Engage the parking brake.
If your vehicle requires it, drive the vehicle for a short time to warm the
transmission fluid. Warm fluid drains more completely.
Safely raise the vehicle using a jack and jack stands or ramps.
Locate the Drain Plug:
The drain plug is usually located on the bottom of the transmission pan.
Consult your vehicle's service manual for the exact location.
Drain the Old Fluid:
Position the drain pan under the drain plug.
Carefully loosen the drain plug with a wrench or socket. Be cautious,
as the fluid may be hot.
Allow the fluid to drain completely.
Inspect the drain plug and replace the gasket if necessary.
Clean any debris from the drain plug.
Reinstall the drain plug and tighten it to the manufacturer's specified
torque.
Locate the Fill Plug/Dipstick:
The fill plug or dipstick tube is usually located on the side or top of the
transmission.
Consult your vehicle's service manual for the exact location.
Fill with New Fluid:
Using a funnel, carefully pour the new transmission fluid into the fill
hole.
Fill to the correct level, as specified in your vehicle's service manual.
If your car has a dipstick, check the fluid level with the dipstick.
Automatic transmissions often require the engine to be running, and
the transmission to be in park, when checking the fluid level.
Check for Leaks:
Start the engine and allow it to idle.
Shift through all gear positions (if automatic).
Check for leaks around the drain plug and fill plug.
Recheck the fluid level.
Lower the Vehicle:
Carefully lower the vehicle.
Dispose of Old Fluid:
Dispose of the used transmission fluid responsibly according to local
regulations.
Basic Transmission Operation
The transmission's primary function is to transfer power from the engine to the
wheels while allowing for variations in speed and torque. It achieves this by changing
gear ratios.
Manual Transmissions:
The driver manually selects gears using a shift lever.
A clutch is used to disengage the engine from the transmission during
gear changes.
Gears are engaged by sliding them along shafts using shift forks.
Different gear ratios provide varying levels of torque and speed. Lower
gears provide more torque for acceleration, while higher gears provide
higher speeds for cruising.
Automatic Transmissions:
Gears are changed automatically by the transmission based on vehicle
speed, engine load, and driver input.
A torque converter replaces the clutch, using fluid to transmit power.
Planetary gear sets are used to achieve different gear ratios.
Hydraulic pressure and electronic controls manage gear shifts.
Modern automatic transmissions use sophisticated control systems that
adapt to driving conditions.
Common Transmission Faults
Manual Transmissions:
Grinding Gears: Caused by worn synchronizers, which prevent gears
from meshing smoothly.
Difficulty Shifting: Can be due to clutch problems, worn shift linkages,
or low transmission fluid.
Popping Out of Gear: Indicates worn gears or shift forks.
Clutch Slipping: Worn clutch disc or pressure plate.
Leaking seals: result in low fluid levels.
Automatic Transmissions:
Slipping Gears: The transmission fails to maintain the selected gear,
often due to low fluid or worn clutches.
Rough or Delayed Shifts: Can be caused by low fluid, valve body
problems, or solenoid failures.
No Movement: May indicate a problem with the torque converter,
pump, or internal components.
Fluid Leaks: Result in low fluid levels, leading to various issues.
Overheating: Caused by low fluid, heavy towing, or internal problems.
Check Engine Light/Transmission Codes: Modern transmissions are
electronically controlled, and faults will trigger diagnostic trouble codes.
Torque Converter Problems: shuddering, or complete failure.
General Transmission Issues:
Contaminated Fluid: Old or contaminated fluid can damage internal
components.
Low Fluid Levels: Result from leaks or improper filling, leading to
various problems.
Worn Bearings or Gears: Can result in noise and vibration.
Electronic Control Problems: Faulty sensors, solenoids, or control
modules can disrupt transmission operation.
Linkage problems: Cables, or mechanical linkages wear out, and
cause shifting problems.
