Drive Train
Diagnostic St. Louis Auto Repair 
To make the power produced by the engine usable, the rotary motion and torque of the engine’s crankshaft travels through a transmission and drivetrain through the axles to the drive wheels. The word Drivetrain is used to refer to how the wheels are driven.
How a vehicle’s drivetrain is laid out defines the type and use of the vehicle. Some cars and SUVs are available as All Wheel Drive, but the basic layout of how the wheels are driven is based on if the vehicle will be RWD (rear wheel drive) or FWD (front wheel drive). The placement of the components of the drivetrain under the vehicle can reduce space for passengers, cargo and other items.
Most Trucks and SUVs are RWD or a 4WD configuration and many performance sports cars are RWD. This configuration puts the driving components along the center line of the vehicle and power flows from the rear of the transmission through a driveshaft and into the differential. The differential is what drives the rear wheels. To do this, it must take the power from the engine and turn it 90 degrees to power the rear axles. It is accomplished through a system of gears that are splined together at a 90 degree angle inside the differential. This system of gears not only drives the rear wheels, but it allows for torque to be distributed to both rear wheels even when they are turning at different speeds, such as when the vehicle is turning a corner. Sometimes there can be an uneven distribution of power to the separate wheels and some differentials have a clutch pack to help offset this problem. This kind of differential can be referred to as posi-traction, sure-grip or equal-lock.
For FWD vehicles; which are many of our modern cars and smaller SUVs, there is more room for seating because there is not a rear differential taking up valuable space under the vehicle. These vehicles tend to get better poor-weather traction, which is an added benefit. This configuration incorporates the transmission and differential into one unit, called a transaxle. This bolts directly onto the engine and transfers power to the wheels through two independent drive shafts, often called constant velocity or CV shafts. In addition to driving the front wheels, CV shafts must allow for left/right steering and the up and down movements of the suspension. Unlike the U Joints used in RWD drivetrains, CV Joints and shafts are used.
Differential and other Drive Train problems normally start as some sort of abnormal noise or vibration. Our Technicians will gather as much information from the driver of the vehicle as possible. Does it make noise when accelerating, coasting or turning corners? A test drive will be required and a physical inspection of exposed parts to look for damage and/or leaking parts is the next step. Sometimes a technician may need to use a stethoscope or other device to try to isolate the exact source of a noise.
When you hear an odd noise coming from under your vehicle, give our Service Representative a call at Jammin’ J Auto to schedule a time for our Technicians to see whether your vehicle is in need of repair.