Perrin Pitch Stop MountReduce drivetrain shudder under hard acceleration by installing a PERRIN Pitch Stop Mount. Subarus with power and drivetrain upgrades will need PERRIN's more aggressive option. What Does A Pitch Stop Mount Do? Under hard acceleration, the drivetrain is being twisted front to back from the front axle torque twist. To control this front to back twisting, Subaru created a pitch stop mount. The factory pitch stop is made of plastic with soft rubber