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48RE Transmission Rebuild And Install

A Bulletproof Transmission: A Half-Century in the Making

Text By Jason Thompson, Photography by Jason Thompson

If we don’t count the addition of electronic controls and gradual mechanical and fluid dynamic improvements—the basic design of the 48RE Chrysler transmission found in our ’06 Dodge Ram 2500 has been in production 52 years. This legacy is good for two reasons: First, it means the initial foundation was solid, and secondly, it gave plenty of time for performance shops to beef up the internals one destructed part at a time—until it became bulletproof. Besides stronger parts, transmission gurus such as Ernie Davis at Sun Coast Converters have invented and refined new control strategies so parts stay alive, even during extreme racing conditions. Follow along as we look at the origins, development, and installation of a Dodge 48RE transmission, which stands for: (4) four speeds, (8) level eight torque rating, (R) rear-wheel drive, and (E) electronically controlled transmission.

Simpson Planetary Gearset
In 1956, Chrysler licensed Howard Simpson’s transmission gearset technology and the legendary TorqueFlite instantly became the envy of the world. A few years later, GM, Ford, and a few others bought the Simpson design and adapted it to their transmissions. All stayed relatively unchanged at the basic level until the ’90s in cars and ’10s in trucks. The Simpson planetary gearset consists of two planetaries connected by a sun gear. The heart of an automatic transmission is the planetary gearset. Planetary gearsets allow a transmission to have several different gear ratios, with different clutches holding certain components stationary.

Planetary gearsets are made up of a sun gear, planet gears, the planet gears’ carrier, and the ring gear (also known as the annulus gear). Each of these three components can be the input, output, or can simply be held stationary. Two clutches and two bands are able to manipulate three forward gears, one neutral, and one reverse speed. In later four-speed transmissions, a third planetary is located in a housing bolted to the rear of the main case (it’s also controlled by a clutch).

The Simpson legacy lives on in the trucks we drive today and in the SAE/Timken-Howard Simpson Automotive Transmission and Driveline Innovation Award, which was established in 2007. If you want to learn more about Howard Simpson, check out “Man with a Pencil: Engineering Genius of the Modern Automatic Transmission,” Motor Trend, Vol. 16, No. 10, Oct. 1964, page 82-85.

Driving a Bulletproof Transmission
Dodge’s four-speed automatic transmissions require an aggressive shift pattern and increased line pressure to cope with the torque of a modified Cummins. The owner of the ’06 Dodge Ram in this article was at first alarmed by the firmness of the shifts from the Sun Coast 48RE we installed. This is a common experience, as worn-out transmissions have a tendency to feel smoother than they should as they are slipping their way into oblivion. In our experience, once the owner gets the feel for when the truck likes to shift, the new combination is very fun to drive.

By Jason Thompson
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