Forged chromoly 1350-series driveshaft slip yoke, 31 splines, for the Ford C6, FMX and 31-spline T56 and ZF five-speed output shafts.
A Ford truck or muscle car with a C6 that keeps wetting the back of the extension housing, clunks when you step on it from a stop, or is getting a bigger engine and a stronger driveshaft usually ends up needing a new slip yoke. This one is forged chromoly with an oxide finish, cut for a 31-spline output shaft and machined for a 1350-series U-joint. It cross-references the 3-3-2491X pattern and Sonnax T3-3-2491HP, and the yoke is stamped 863-68. Besides the C6 it fits the FMX, T170 and TK600, the Tremec T56 and T56 Magnum with a 31-spline output, and the ZF five-speed.
The slip yoke is the front end of the driveshaft. Its internal splines slide over the C6 output shaft, and the smooth outside barrel runs in the extension housing bushing with the rear seal lip riding on it. When the rear axle moves up and down, the driveshaft has to get longer and shorter, and the yoke does that by sliding in and out of the housing. The 1350 ears hold the front U-joint, so the full output torque of the transmission goes through those 31 splines. That makes the yoke a wear part on both ends: the barrel wears against the bushing and seal, and the splines wear against the output shaft.
The 1350 joint is the reason people pick this part over a stock-style yoke. Sonnax's U-joint chart puts the 1350 at the same 3.622 inch width as a 1330 but with a 1.188 inch cap instead of 1.062, so the cross and bearings are bigger. On a C6 behind a big-block, a heavy trailer or a lot of tire, that moves the weak link off the front joint.
Grab the driveshaft just behind the extension housing and push it up and down. A little movement is normal; a lot means the bushing is worn, and a new yoke in a loose bushing will eat the next seal too. Then pull the driveshaft, wipe the barrel and drag a fingernail across the seal track. If it catches, the yoke is done. Our C6 fluid leak guide walks through telling a rear seal leak from a pan, filler tube or cooler line leak, and the C6 noise diagnosis guide covers separating a driveline clunk from an internal transmission problem before you spend money on either.
Listed fitment: Ford C6, FMX, T170 and TK600; T56 and T56 Magnum with a 31-spline output shaft; ZF five-speed. Measurements off this yoke are a 4.72 inch barrel length, 6.45 inches from the U-joint centerline to the end of the barrel, a 1.685 inch journal diameter where the seal rides, full splines with no counterbore, and a weight of 3.06 lb. Sonnax publishes 4.750 and 6.440 inches for its T3-3-2491HP, so the two are the same pattern within normal machining tolerance.
Count the splines on the output shaft before you order. Ford used both 28 and 31 spline output shafts behind its automatics, and the yoke will not start on the wrong one. Sonnax recommends counting on the shaft rather than the old yoke because some yokes have a missing spline. On a 4x4 C6 the transmission bolts to a transfer case, so this yoke is for 2WD units; our C6 identification guide helps confirm which unit you have. If you changed ride height or swapped transmissions, measure how much barrel stays in the bushing at ride height before you cut a driveshaft. If you are not sure, send us the year and VIN or your measurements, or browse more driveline parts under hard parts.
| Fits | |
| Spline count | |
| U-joint series | |
| U-joint journal diameter | |
| Barrel length | |
| U-joint centerline to end | |
| Material | |
| Replaces | |
| Weight |
No. It is cut for a 31-spline output shaft. Count the splines on the shaft itself before ordering, because a 28-spline yoke and a 31-spline yoke look close on the bench but will not interchange.
The front U-joint and the driveshaft tube yoke must be 1350 series to match. If your shaft was built with a 1310 joint, you need a driveshaft or a front tube yoke built for 1350.
Often, yes. A groove worn into the barrel where the seal lip rides will cut a new seal quickly. A worn extension housing bushing does the same thing, so check shaft play and replace the bushing with the yoke.
On 4x4 trucks the C6 bolts to a transfer case and there is no slip yoke at the transmission. This part is for 2WD C6 units and the other listed manual and automatic transmissions.
Use what your C6 was built for. Early units were designed around Ford Type F, and by 1996 Ford specified MERCON. Check the level with the engine running after the driveshaft is back in.
