Reverse in an Overdrive relies on springs and friction.

Basic internals of an OD.

A cone shaped device called a sliding member by the manufacturer and "cone clutch" by a lot of people has friction material on its inside and outside surfaces. It also carries the sun gear of the planetary gear system for OD mode. The sliding member is pushed against a bell shaped output device that contains the ring gear of the planatary system on its inside and the "One way clutch" for gears one to four.

When the OD is OFF, this sliding member is pushed againt a bell shaped output device by springs and spins with the transmission output shaft. The trans shaft also drives a sprag bearing inside the bell shaped output shaft of the OD.

A Sprag bearing is a series of rollers resting on a multiple cam "race" driven by the trans output shaft. When in forward mode, the trans turns the cam and the rollers are pushed out against the outer race and drives the auto forward.

When in OD mode, the output bell is turned faster than the cam can push the rolles out and the Sprag then "freewheels" allowing the output to turn faster given OD mode.

This Sprag freewheeling does not allow reverse. The friction material between the sliding member and the output bell is all that allows reverse.

Causes of no or poor reverse.

Worn lining on the inside of the sliding member.

Incomplete release of fluid from the OD on circuit holds the sliding member off the output device.

A sliding member that is in two pieces, which also would not allow forward OD mode to occur.

Any one of about seven or eight parts that get "stuck" not allowing free movement of the sliding memmber.

Duane