Automatic Transmission Pumps: The Heart Of Your Transmission

Posted by on Wednesday, November 28th, 2012

Just as the heart is critical to the human body, so to is the pump in an automatic transmission. Without a properly working pump, your transmission will not function as it was designed to, or worse, it won’t function at all.

Front Pump for an Automatic Transmission


Think of your transmission pump as the heart of the system. The transmission’s blood is its hydraulic fluid. It’s kind of ironic that most transmission fluid is the same color as human blood. Your heart pumps blood to the body so that its parts can function. Clogged arteries don’t allow blood to reach the extremities. Poor circulation causes our bodies to fail, and a faulty pump has the same effect on your transmission.

The transmission builds hydraulic pressure to permit other components of the transmission to function. Automatic transmissions use what is called a gear pump. They usually contain two gears. The inner gear is driven by the torque converter hub (the hub is slotted to engage the inner gear). Take great care when installing the torque converter in your transmission. Not properly lining up and seating the torque converter can damage the transmission’s inner gear. The second gear, referred to as the outer gear, is driven by the inner gear. As the gears turn and mesh together, they create a vacuum that sucks up the transmission fluid. As the gears turn they create pressure in the fluid, which results in a pressure increase in the hydraulic system.

Pump in an Automatic Transmission


The pressurized fluid is used to move valves in the valve body, and to apply clutch packs and bands. It is also used to lubricate the internal components in the transmission, as well as carry fluid to the transmission cooler. Common problems with the transmission pump include: 1) Assembly errors by the manufacturer or re-builder. 2) Using gaskets of the wrong thickness. 3) Broken drive (inner) gear. 4) Worn tolerances between the inner and outer gear teeth. 5) Worn tolerances at the front and back of the pump. 6) A broken pressure relief spring, worn out or installed improperly.

Automatic Transmission Gears


Some front pumps make a whining noise when they start to fail. Since the pump is directly connected to the motor via the torque converter housing, the motor must be turning for the pump to operate correctly. The best way to test a pump is to use a pressure gauge and attach it to the pressure port on the transmission. The minimum and maximum pressures are listed in the dealer’s manual and are widely available on the internet.

Remanufactured Automatic Transmission


When replacing a defective transmission I always use a re-manufactured transmission. Re-manufacturers will machine the front pump or replace the gear to bring it to better than new condition.

41 Willys with Automatic Transmission


Without a pump your transmission would not work. Like your own heart, you want to do everything you can to extend its life.  A pump failure means that you’ll have to leave the car at home, and put on your walking shoes.  Take care of your transmission’s pump and you’ll reduce the chances of transmission failure.

 I highly recommend you replace your customer’s transmission with a re-manufactured transmission. A remanufactured unit will include major alterations and upgrades designed to make them both stronger and more durable. A re-manufactured transmission will also include a much better warranty; three years compared to an average 90 days for a rebuilt transmission. As a bonus, in the rare event that a re-manufactured transmission fails within the warranty period, they will cover your R&R cost to replace your customer’s transmission. And remember, the companies that re-manufacture transmissions are very easy to contact. They are just a quick phone call or email away from helping you out.

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