4R70W Servo and Accumulator Piston Kit 6-Piece Set

This is the servo and accumulator piston set for Ford's AODE family: six bonded rubber-to-metal pistons plus the covers and the overdrive snap ring, sold as one kit under WIT part number A76902HK. It covers the overdrive servo piston (OE F75Z-7H188-AA), the three-groove low/reverse servo piston (E0AZ-7D189C) and its cover (E0AZ-7D036-A), the 1-2 accumulator piston (F7AZ-7F251AA) and cover (F4AZ-7F247A), and the 2-3 accumulator bonded piston (F7AZ-7H292AB).

These are the parts behind the usual complaints on high-mileage AODE, 4R70W, 4R70E, 4R75E and 4R75W units. The bonded rubber on the original pistons goes hard and cracks, so the servo and accumulator circuits leak internally. What you feel is a long, flaring 1-2 or 2-3 shift, a soft or delayed overdrive apply, and low reverse band apply that turns into a bang into reverse or no reverse when the unit is hot. Replacing seals alone will not fix it once the bonded piston material is checked or split -- the whole piston has to come out.

On the bench the servo pistons come out of the case bore once the cover snap ring is released; a small screwdriver or a servo capsule tool walks the cover down far enough for the ring to clear. Lube the new pistons with ATF before they go in, seat each cover square in its bore, and check overdrive servo pin travel before the pan goes back on. Note that the low/reverse piston in this kit uses a three-groove guide pin -- some earlier cores run a two-groove pin, so keep your original pin if that is what your unit has.

Fitment covers many 1992-2012 Ford, Lincoln and Mercury rear-wheel-drive applications with these transmissions: Crown Victoria, Grand Marquis, Town Car, Mustang 1994-2004, Thunderbird, Mark VIII, Cougar, Explorer and Mountaineer 5.0L 1996-2001, Expedition 4.6L, Mark LT, and F150, F250, E150, E250 and E350 with the 14-bolt pan. Verify transmission model, year, engine and pan bolt count before ordering.