Chrysler 545RFE / 45RFE / 68RFE

Chrysler's rear-drive automatic family — in the Grand Cherokee, Commander, Liberty, Wrangler JK, Durango, Dakota and the Ram 1500 and 2500.

The name is the first thing worth explaining, because it is unusual and it is not a marketing flourish. The 45RFE was built with two second gears — a wider one used only when kicking down — so the later 545RFE advertised five ratios by counting a gear the transmission had all along and now uses on the way up as well. A Jeep whose paperwork says four speeds and whose scan tool reports five is very often the same gearbox, and neither document is wrong.

Its dominant failure is the solenoid pack and its integral pressure sensor, which produces a limp mode locked in a single gear, harsh engagement, or an inability to select reverse. It looks and feels exactly like a failed transmission, and it is a bolt-on part — worth eliminating before anything more is contemplated.

The second recurring theme is that these units run their fluid hot, especially towing, and the overdrive clutch is what pays for it. A transmission cooler is a preventative measure on these rather than an accessory.

The 68RFE is the heavy-duty diesel version and is not interchangeable with it, despite the shared naming; a procedure written for a 545RFE behind a 4.7 V8 does not describe the gearbox behind a Cummins.

The name is three gearboxes and three ratio counts. The 45RFE is a four, the 545RFE a five and the 68RFE a six — and they share a case and a great deal of hardware, which is why they sit together. A ratio, a fluid capacity or a solenoid pack quoted for one does not transfer, so establish the number stamped on the unit before ordering.