Transmission problems in a vehicle can be the cause of one of the most major repairs a car owner can make to their vehicle. Transmission repair typically requires a specially trained mechanic and several thousands of dollars. Without a properly functioning transmission, a car might not move or operate correctly when you attempt to drive it. There are several different reasons for a car transmission to beginning making a clunking noise. It is important to determine why a transmission is clunking and attempt to have it serviced or repaired before permanent, irreparable damage is done.
Low Transmission Fluid
One of the most common reasons a transmission will make clunking noises when shifting is because it has run low on transmission fluid and lacks the lubrication to keep shifting smoothly. Low or too old transmission fluid will not provide proper lubrication and cooling for the various components and will lead to hard shifting and the accompanying clunking noises.
You can tell if transmission fluid is too old by checking it and paying attention to its color and consistency. Transmission fluid should be red or dark pink and translucent. Brown, black or cloudy transmission fluid is old, burned or contaminated with other fluids.
A large number of bearings, gears, springs and other components are inside your transmission that allow it to shift between gears. A problem with any one of these parts can cause the transmission not to shift properly or to shift hard, which commonly accompanies the clunking noise. These sorts of problems must be diagnosed by a professional because the transmission must be removed from the vehicle and taken apart to locate the problem.
Most newer vehicles have their transmissions controled by a number of computerized sensors. If these sensors begin to send the wrong speed or shifting information, it can cause an automatic transmission to have shifting problems and cause clunking noises while the car is shifting gears. The speed sensor is especially prone to causing this type of transmission problem because the vehicle's computer is not properly regulating performance for the correct speed of the car.
Engine and Transmission Mounts
In some cases, the clunking you are hearing is because of a broken or loose transmission or engine mount allowing the engine and transmission to move when your vehicle is shifted into gear or significantly changes speeds. This can be detected by lifting the vehicle and examining the various mounting points that support the transmission and engine to hold them in place. Faulty universal joints can also be mistaken as a clunking transmission because they will cause the drivetrain to make clunking noises when accelerating and decelerating.