← Tech

RFE automatics (45RFE / 545RFE)

The Grand Cherokee V8 box, with a two-second-gear trick

When the 4.7 V8s arrived, the Grand Cherokee WJ debuted a cleverly designed automatic: the 45RFE, with three planetary gearsets and an "extra" second gear for smoother launches. From 2001 it evolved into the 545RFE, with a real fifth gear thanks to a second overdrive enabled in software.

The two-second-gears trick

The RFE's most striking feature is its two second-gear ratios. With three planetaries, the box has a "normal" 2nd of 1.67 used when accelerating up through the gears, and a taller alternate 2nd of 1.50 that only appears on hard downshifts (4→2 kickdown) at speed, to drop in more smoothly and improve highway passing. It's transparent to the driver: the box picks which to use as needed.

In practice the 45RFE and 545RFE are the same box: the 545RFE adds the fifth (0.67) in electronic control. That's why they read as 4- or 5-speed depending on the year and software.

Capable but demanding

The RFE is smooth, capable and handles V8 torque, including the 5.7 Hemi that came later in the WK. But it's a modern, solenoid-heavy box: it demands tidy fluid (ATF+4) and filter maintenance, and won't forgive neglect. A skipped fluid change or a clogged cooler are the most common causes of erratic shifting.

Outside the Grand Cherokee, the 545RFE was used with the 4.7, the 4.7 H.O. and the 5.7 Hemi across several Chrysler models, and even behind the 2.8 CRD turbodiesel in some export JKs. It's the family's true 'highway-miles' automatic.

Specifications