The Ins and Outs of Buying an Automatic Transmission Gasket
An automatic transmission gasket is a gasket (a piece or ring of rubber shaped to seal the junction between two surfaces) that mechanically seals your transmission, filling the space between mating surfaces to connect them together (in this case, it's the transmission and the oil pan). Depending on the type of gasket you're buying, you could either use gasket cement or adhesive on it or not. The instructions that come along with the gasket kit should clarify this point. The auto transmission gasket you should get will mostly depend on what type of pan you have.
Gasket Shopping: Types of Gaskets to Choose From
- Pure Cork and Cork/Rubber Gaskets (with Rubber Coating): Pure cork is the rarest type of material for your automatic transmission gasket. You're likelier to come across cork and rubber gaskets or cork and rubber gaskets with rubber coating (which replaced pure cork gaskets a long time ago). They're all the gaskets you can depend on with automatic transmissions that have flat surfaces, raised surfaces, or recessed ribs between pan holes.
- Nitrile Rubber Gasket: This is one of the most commonly used gasket types. Like with cork/rubber and cork/rubber with rubber coating, it covers and seals a large range of pan types and surfaces and deals with flat surfaces, raised surfaces, or recessed ribs between pan holes. Nitrile rubber is a common gasket material because of its tensile strength, abrasion resistance, good compression set, and resistance to heat, abrasion, water, or gas permeability.
- Neoprene Rubber Gasket: This is also one of the most commonly used gasket types. It's best used for continuous ribbed pans and flat surfaces. Neoprene is renowned for its impermeability and incompressibility. No liquids or gases can pass through its tight barrier or impermeable seal. It can also be deformed but it can never be reduced in volume. It has a maximum temperature of 250 °F, a minimum temperature of 20 °F, and maximum pressure of 250 PSI.
- Formed Rubber Gasket: Formed rubber (also known as molded rubber) specifically deals with lipped pans. It's also a special application gasket that deals with lipped pans for BMW, Volkswagen, and Mercedes transmissions. This gasket type fits over the pan's edge before the pan itself is bolted unto the transmission. Afterwards, the sealing is done. It's one of the more customizable gasket materials out there.
- Plastic/Rubber with Metal Torque (Reusable Gasket) or Silicone Rubber Adhesive Sealant: The silicone rubber adhesive sealant is for specific applications only, mostly of the flat surface kind. Ditto when it comes to plastic/rubber with metal torque (the reusable gasket type). Only a small bead of sealant is required to make the seal between the pan and the transmission. Reusable gaskets, meanwhile, include metal cylinders located at every bolt hole to limit the chances of over-tightening or over-torque.
Last Points to Ponder
When buying a gasket, there are many types of materials to choose from. Sometimes, it's enough to replace your damaged gasket with a duplicate of it, but other times you have the opportunity to upgrade your gasket to a better material. Regardless, unless you drive a BMW, Volkswagen, or Mercedes, you're likely to buy some variant of the cork/rubber, nitrile rubber, or neoprene rubber gasket. Consult your mechanic or dealership for more details and what your best gasket options are.