Transmission Bearings

Automatic and manual transmissions have a number of bearings that allow shafts, gears, and other components to rotate freely with minimal friction while transferring power from the engine to the drivetrain. Although there are dedicated bearings that are designed and sized for specific locations and components in every transmission, the type of bearing will fall into one of the following categories: ball bearings, roller bearings, tapered roller bearings, needle bearings, caged needle bearings, and thrust bearings. In addition to bearings, some shafts turn on bushings, and thrust washers are used to control shaft end-play and clearance.

Friction consumes power, accelerates wear, and creates heat, all conditions that are detrimental to the function of a transmission. To minimize friction the balls or rollers in bearings roll on the smooth surfaces of inner and outer races. The inner bearing race surrounds the rotating shaft, while the outer race fits into the transmission case. Ball bearings are used in high shaft speed applications where there are radial (perpendicular to the shaft) and axial (parallel to the shaft) loads. Roller bearings can handle heavier loads because the load is spread across the roller, unlike the ball’s relatively small point of contact. Needle bearings are just roller bearings with small diameter rollers. Tapered roller bearings are pre-loaded during installation. Thrust bearings are used where there are high axial loads. Although there are ball thrust bearings, they are more commonly roller bearings because of their higher load bearing capacity.

In some transmission applications a bushing is used instead a bearing. A bushing is a type of plain bearing in that the shaft rotates on a thin film of lubricant. Most bushings are made of bronze and are a press fit into a bore. Some are grooved to allow oil to enter and lubricate the bushing, while others have a hole which must be aligned with the lubricant passage in the case. There are also sintered bronze “oilite” bushings that are porous and impregnated with oil during the manufacturing process, providing all the lubricant the bushing will need during operation. Clutch pilot bushings are a common sintered bronze bushing application. Thrust washers, also known as thrust plates or thrust bearings, are used to absorb axial loads and to separate parts and prevent wear. They can be made of sintered bronze, steel, and even plastic depending on application. Many thrust washers come in different thicknesses and are used to set end-play or clearance to specification during transmission assembly.

The input shaft on a typical manual transmission is supported at the rear by a ball or roller bearing in the transmission case and at the front by a bushing or bearing in the end of the crankshaft or the center of the flywheel. The output shaft is supported at the front by a roller bearing inside the input shaft, at the center by a ball or roller bearing, and at the rear by a bearing or bushing in the extension housing. The transmission countershaft rotates on needle roller bearings with thrust washers at each end. The clutch release bearing, also called a clutch throw-out bearing, is a ball thrust bearing supported on a carrier that slides on a hollow shaft extending from the front of the transmission and encircling the transmission input shaft. The release bearing is attached to a clutch fork or lever that pivots at one end or in the center and is attached to a slave cylinder, cable, or pushrod at the other end.

Automatic transmissions employ numerous bearings, bushings, thrust bearings and thrust washers including those at the turbine shaft, planetary gearset and clutch components. Both manual and automatic transaxles have bearings at the drive chain or drive gear, and transaxle final drive pinion and differential case. Upon transmission disassembly the bearings should be thoroughly cleaned and felt for roughness, looseness, and noise as the bearing is rotated. Visually inspect balls, rollers and races for signs of scoring, spalling, brinelling, peeling, corrosion, and any other signs of damage. Bushings can be visually inspected, the shaft-to-bushing clearance can be checked, and the inside diameter and shaft diameter can be measured and compared with specification. Transmission shafts should be checked for scoring or other damage where the bushing or bearing contacts the shaft. The fit of the bearing outside diameter in the transmission case or other components should also be checked.

Regardless of the type of transmission and bearings on your car or truck, or the damage incurred, we have the replacement bearing assemblies, bushings, and thrust washers to help restore transmission performance and quiet operation. All parts are manufactured to meet or exceed the vehicle manufacturer’s specifications, so you can be assured of precise fitment, flawless performance, and long lasting durability.