Which of the following planetary gear train control devices can sometimes be adjusted from the outside of the transmission?

• A. The hydraulic clutch
• B. The sprag-type one-way clutch
• C. The servo and band mechanism
• D. The roller-type one-way clutch

Answer: (C)

In planetary gear train control, the element that can sometimes be adjusted from outside the transmission is the servo and band mechanism. This system uses a band wrapped around a drum, with a servo actuator applying hydraulic pressure to tighten the band. Many transmissions provide an exterior adjustment to set the band clearance or lash, which directly affects how the band engages the drum and, therefore, shift quality and clutch hold. The other devices are generally fixed internally: a hydraulic clutch is controlled by the valve body pressure but isn’t adjusted via an external screw or bolt, and sprag-type or roller-type one-way clutches are self-contained friction devices whose preloads and geometry aren’t adjusted from outside.