Guide To Automatic Overdrive Transmissions

AOD-E/4R70W

Ford updated the AOD in the early '90s, strengthening it substantially and adding electronic shift control. It was soon equipped with a new, wide-ratio gearset and renamed 4R70W-and is one of the best transmissions Ford has ever made. "They can handle a lot of abuse," Baumann says.

Manufactured: 1992 to 2005 OE rating: 350 hp Strengths: 2-inch-wide overdrive band for better holding power; stronger input shaft; torque converter is locked up by a clutch that can be pulse-width-modulated by the ECM; the 4R70W has a wide-ratio gearset that better matches shifts to engine powerband. Weaknesses: Needs computer to operate. Build it with: Heavy-duty direct clutch pack; 4R70W gears in an AOD-E; Baumann's ReCal-Pro valvebody calibration kit; Baumannator TCS transmission controller. Can be built to handle: 700 lb-ft Notes: The best transmissions to get are from '98-and-later cars; 4R70Ws from '96 to '01 Explorers and 3.8L or 4.2L V-6 Mustangs have a Windsor engine bellhousing bolt pattern, making them ideal swap candidates.

Chrysler

A500

Chrysler added a Fourth gear to the 904, and the A-500 was born. Fourth gear and torque converter lockup are activated electronically via computer control.

Left to right: Chrysler's A518, 727, A500, and 904.

Manufactured: 1989 to 2007 OE rating: 275 hp Strength: Can be built with heavy-duty 904 parts. Weaknesses: Light-duty transmission; small clutches and bands; oiling problems cause overheating, especially of the output shaft; need to wire a switch to engage Fourth gear and lockup converter. Build it with: Five-clutch direct clutch pack; wide front and rear bands; four-pinion planetary gears; Phoenix Transmission's wiring for Fourth gear engagement and torque converter lockup. Can be built to handle: 400 hp

A518

Operating with a similar plan, Chrysler engineers, needing a heavy-duty overdrive trans, added a Fourth gear to the 727 TorqueFlite three-speed, creating the A518. It was original equipment in Dodge trucks. Manufactured: 1990 to 2007 OE rating: 350 hp Strengths: Heavy-duty design based on the 727; can be built with strong 727 parts. Weaknesses: Oiling problems can burn up the output shaft; need to wire a switch to engage Fourth gear and lockup converter; giant size makes it difficult to fit in older body styles; they may not clear the torsion bar mounts on some body styles. Build it with: Four-pinion front planetary gear; heavy-duty intermediate band strut; high-capacity direct clutch drum; Phoenix Transmission's wiring for Fourth gear engagement and torque converter. Can be built to handle: 500 hp Notes: The A518 can be built to fit behind B- and RB-series engines.

By John McGann

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