Which planetary gear control element is commonly adjustable from outside the transmission housing?

• A. Hydraulic clutch
• B. Sprag-type one-way clutch
• C. Servo and band mechanism
• D. Roller-type one-way clutch

Answer: (C)

The servo and band mechanism is the element commonly adjustable from outside the transmission housing. In an automatic transmission, the band acts as a brake on a drum to hold parts of the gear train in certain ranges, and the servo applies that band through hydraulic pressure. There’s usually an access point on the outside of the case—a screw or adjuster—that lets a technician set the initial band clearance and the apply force. This external adjustment is important because the band wears with use, and re-tuning it helps maintain proper holding power and prevent slipping during gear engagement.

The other options aren’t typically adjusted from outside the case: the hydraulic clutch is controlled by internal hydraulic pressure and valve body electronics rather than a user-accessible external screw; sprag-type and roller-type one-way clutches operate with fixed preload and clearances and don’t have external adjustment points.