C6 Transmission Slip Yoke 31-Spline 1350 Chromoly

This is the driveshaft slip yoke that rides on the transmission output shaft and slides in and out of the extension housing as the suspension cycles. It carries the front universal joint of the driveshaft, so it takes every bit of torque the transmission puts out. This one is forged chromoly with an oxide finish, cut for a 31-spline output shaft and machined for a 1350-series u-joint.

Fitment as listed by the manufacturer: Ford C6, FMX, T170 and TK600, plus the T56 and T56 Magnum with a 31-spline output shaft and the ZF five-speed. Part number references are OE 3-3-2491X and Sonnax T3-3-2491HP; the manufacturer stamps it 863-68. Count the splines on your output shaft before you order. A 28-spline C6 shaft and a 31-spline C6 shaft look close enough on the bench to fool you, and the yoke will not start on the wrong one.

Measurements off the yoke: barrel length 4.72 in, u-joint centerline to the end of the barrel 6.45 in, u-joint journal diameter 1.685 in as listed, weight 3.06 lb. Those numbers matter because slip yoke length sets how much of the barrel stays inside the tailhousing bushing at ride height. If you swapped transmissions or changed ride height, measure the engagement before you cut a driveshaft to length.

The problem this fixes is a yoke that has worn out. A scored or ovaled barrel chews the extension housing bushing, and once that bushing is loose the output shaft seal starts weeping and the driveshaft sets up a vibration you can feel through the floor at highway speed. The other reason to put this in is a 1350 conversion: the smaller 1310 joint is the weak link on a built C6 behind a big-block, and going to a forged chromoly 1350 yoke moves the failure point away from the driveshaft. When you install it, replace the extension housing bushing and seal at the same time, and grease the splines - a dry yoke binds under load and beats the bushing out again.