Automatic Transmission Seals
Automatic transmission seals are used to contain pressure and prevent leakage. These seals are made of metal, synthetic rubber, and Teflon. They can also be either positive or non-positive. A positive seal contains all fluid, a non-positive seal allows a small amount of fluid past for lubrication of moving parts.
Lip Seals: Lip seals are ideal for both rotational and axial movement. They are used to apply pressure. Piston seals are a member of the lip seal family, vital to transmission performance. This type of lip seal has the lip on the outside of its diameter. As high pressure fluid pushes on one side of the lip, it forces the seal firmly against the cylinder wall moving the piston forward. Notice in the illustration that it's important to make sure a piston’s lip seal is facing in the right direction. If installed incorrectly, the seal will not hold pressure. Lip-type seals are also used to contain fluid from leaking past both transmission and axle shafts. This type of lip seal has the lip on the inside diameter supported by a garter spring. The spring is used to apply a constant force as the seal wears.
O-rings: O-rings are often used for static sealing. A static seal is a seal between two non-moving parts. A dynamic seal is a seal between two moving parts, like the lip seal. They work great for creating a positive seal against fluid leakage.
Square Cut Seals: Both square cut seals and O-rings are installed into a groove cut into a component. O-rings are mostly used in static applications, because they tend to roll in the groove when the parts are moved against each other. Square cut seals have less movement in this groove due to their square cut design. They allow for more axial movement than an O-ring.
Metal Ring Seals: Metal seals are used around shafts to provide non-positive sealing. These seals fit into a groove in a shaft and have a gap between the ends of the seal, similar to a lock washer. Teflon seals are used for the same purpose and offer less wear on the related parts. Sometimes there’s a small fastening hook on each end. These seals often come in one circular piece and may require a special installation tool.