Ford 4R70W / AOD-E

Ford's electronically controlled rear-drive four-speed — behind the Panther cars (Crown Victoria, Grand Marquis, Town Car, Marauder), the Mustang, Explorer, Expedition, Bronco and Thunderbird.

It is a very long-lived transmission with one alarming failure mode that is usually cheap. The electronic pressure control solenoid governs line pressure, and when it fails the transmission defaults to maximum pressure — every change lands as a bang, the car feels as though something has broken, and it has not. A sudden onset of violently hard shifts on one of these is the EPC solenoid until proved otherwise, and it is a valve-body part rather than a rebuild.

The genuine wear items are the forward clutch and the overdrive band. A slip that appears only in overdrive, at a steady speed, with the engine rising and the car not, is the band; a slip from rest is the forward clutch. Both are worth catching early, because a clutch pack that has been slipping contaminates the fluid with the material it is shedding and takes the rest of the transmission with it.

It is not the AOD. The earlier gearbox looks the same and is mechanically controlled through a split-torque input — no solenoids, no computer, a different repair and different parts. A listing that says only 4-speed automatic on an early-1990s Ford covers both, and the tell is whether the transmission has an electrical connector on the case at all.