GM replaced the Dual Clutch Dual Band to the next generation Controlled Coupling HydraMatic or Jetaway (Oldsmobile) or StratoFlight or Super HydraMatic (Pontiac) or 315 HydraMatic (Cadillac) or dual-coupling Hydra-Matic. We will refer to all of these variants as simply “Controlled Coupling”.
Controlled Coupling HydraMatic began using sprag clutch and an internal secondary fluid coupling instead of just friction clutches and bands. Shifting was accomplished not only with bands, clutches and sprags, but was also by draining or filling the secondary internal coupling – thus the term “dual coupling”. The dual range feature improved performance and also incorporated a “Park” feature that positioned a pawl into the gear on the reverse carrier.
Controlled Coupling shift schedule was smoother as compared to the original Hydra-Matic and did not require the same amount of periodic maintenance. It was, however, more complex.
Since the Controlled Coupling uses a main coupler in the bell housing, and a secondary internal coupler, this design was subject to a phenomenon called “drain back”. When not running, the main coupler, because of the many bushings used to manage the system, could drain back into the sump. When wear was a factor, the drain back would be more common place. As a driver you would note this as a slip condition on cold start after placing the selector into drive or reverse. The drive clutch is not slipping, but the main coupler is not able to transfer engine torque since it is only partially filled with fluid. The only fix for this condition is a complete rebush of the entire unit (or at least the most worn bushings). This requires special tools to install new bushings and also requires the reaming of a precision pump bushing or reaming the pump housing when it becomes oversized.
Jetaway Rebushing Service
Classic Hydramatic offers a component level rebush service and pump bushing replacement and reaming service. We can do this as part of a standard overhaul (if it is required). Additionally, if you are rebuilding the unit yourself, we offer component level rebush and reaming service where you will simply send the components that require rebush to us. This service is quoted upon request.