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A slip yoke looks like the simplest part in the driveline. It is a splined tube with a U-joint ear on one end. But it does three jobs at once: it transfers every pound of torque from the transmission output shaft to the driveshaft, it slides in and out as the rear axle moves through its travel, and its polished outside diameter is the running surface for the extension housing seal and bushing. Get any one of those wrong and you end up with a leak, a vibration, or a driveshaft that drops on the highway.
Step 1: Count the Output Shaft Splines
Spline count is not negotiable. A 27-spline yoke will not slide onto a 32-spline shaft no matter how close the diameters look. Here are the common counts we are confident in:
| Transmission | Output Splines | Our Yoke |
|---|---|---|
| GM TH350, 700R4, 4L60E | 27 | 1350 slip yoke, 27-spline |
| GM TH400, 4L80E | 32 | Measure and match your series |
| Chrysler A727 (and A833, 30-spline T56) | 30 | Chromoly 1350, 30-spline |
| Ford C6 (and FMX, 31-spline T56) | 31 | Chromoly 1350, 31-spline |
| GM 6L80, 6L90, 8L90, 10L80 | 3-bolt output flange | Flange-to-slip-yoke adapter kit |
Pull the old yoke and count the splines on the shaft, or count the internal splines in the old yoke. The easy way is to mark one spline with a paint pen, then count all the way around until you come back to the mark. Do it twice. An off-by-one count is the most common mistake we see, and 30, 31 and 32 are close enough that a hurried count lands on the wrong one.
Late GM six, eight and ten-speeds use a bolt-on 3-bolt flange at the output instead of a sliding yoke, with the slip built into the driveshaft. The adapter kit converts that flange to a slip yoke so a conventional driveshaft can be used in a swap. If you are weighing one of these swaps, our 4L60E vs 6L80 comparison covers the bigger picture.
Step 2: Check the Seal Surface and Bushing
The yoke barrel rides inside the extension housing (tailshaft) bushing, and the rear seal lip rides on that same surface. A new yoke and a worn bushing is a bad combination, and so is a new seal on a grooved yoke.
Inspect the old yoke
Wipe the barrel clean and run a fingernail across the area where the seal lip rides. If your nail catches on a groove, the yoke is done. A sleeve repair is a gamble on a part that slides through the seal constantly. Also look for a blue or brown heat stain, scoring from a dry bushing, and rust pitting from a truck that sat. Any of those means replace it.
Measure if you are mixing parts
If you are pairing a yoke with a housing that did not come together, measure the barrel OD with a micrometer or a good caliper in a few spots, and measure the bushing ID. Compare to the transmission manual specs for your unit. The yoke should slide into the bushing with no visible side play and no binding.
Replace the bushing and seal with the yoke
If the old yoke was worn, the bushing almost certainly is too. A worn bushing lets the yoke wobble, which wipes out the new seal and shows up as a vibration that people blame on balance. We cover the procedure in extension housing bushing and seal replacement and the seal-only job in how to replace a transmission output shaft seal.
Step 3: Identify the U-Joint Series
The U-joint series has to match on both the yoke and the driveshaft, or you need a conversion joint. Do not eyeball it. 1310 and 1330 joints use the same cap diameter, and 1330 and 1350 share the same width across the caps, so two out of three look similar at a glance. Measure two things on the joint itself:
- Cap diameter: measure across the round bearing cap with a caliper.
- Width across caps: measure from the outside of one cap to the outside of the opposite cap, on the same axis. On outside snap ring joints, measure to the outside of the caps.
| Series | Cap Diameter | Width Across Caps | Typical Use |
|---|---|---|---|
| 1310 | 1.062 in | 3.219 in | Stock cars, light trucks, mild builds |
| 1330 | 1.062 in | 3.625 in | Many stock half-ton trucks, some performance cars |
| 1350 | 1.188 in | 3.625 in | Built V8s, towing, heavier trucks, drag cars |
If you only have the yoke and no joint, measure the inside width between the ears and the bore diameter, and compare to the joint table above. If anything you measure falls between sizes, stop and recheck before ordering.
Forged and Chromoly vs Cast
Factory slip yokes are usually forged steel or, on some lighter applications, cast. Cast is fine for a stock engine in a daily driver. Where it gets marginal is anywhere with sudden torque spikes: hard launches on sticky tires, a trans brake, a big power adder, or a heavy trailer pulled from a stop on a hill. Cast yokes tend to crack without warning.
A chromoly yoke is the right pick when you have added real power or you launch hard. Chromoly is stronger and tougher than plain forged carbon steel. Our 30-spline A727 yoke and 31-spline C6 yoke are both chromoly, which is why they cost more than the 27-spline GM piece. For a TH350 or 700R4 behind a mild small block, the 27-spline 1350 yoke at $84.99 is the sensible buy.
Upgrading 1310 to 1350 When You Add Power
A 1310 joint behind a stock engine will last a very long time. Put a big cam, a blower, or a lot of tire on it and the 1310 becomes the fuse. The 1350 has bigger caps and needles, so it carries more load and holds up better to angle and shock.
You have two ways to get there:
- Full 1350 driveline: 1350 slip yoke, 1350 driveshaft ends, and a 1350 pinion yoke. This is the clean way and the only way we recommend for high power. Pinion yokes for common axles are in our hard parts section.
- Conversion joints: a joint with 1350 caps on one axis and 1310 or 1330 caps on the other. Useful for mixing a new 1350 slip yoke with an existing pinion yoke on a moderate build. It is a compromise, because the smaller side is still the weak link.
Whatever you choose, the driveshaft has to be built or rebuilt with matching tube ends, and it needs to be balanced after any change to the ends. If you already have a shake after a rebuild, start with driveshaft vibration after a transmission rebuild.
Install Notes and Common Mistakes
- Lube the splines and barrel. Clean transmission fluid or the lube the yoke maker specifies on the barrel before it goes into the seal. A dry start can wipe the seal lip.
- Check yoke length and engagement. With the vehicle at ride height, the yoke should be well engaged on the shaft and still have room to slide in on compression. Too long and it bottoms against the transmission. Too short and it can pull off on droop.
- Do not hammer U-joint caps. Use a press. Our OTC 7248 C-frame press handles yokes on and off the shaft, and the Lisle 42890 puller is a good budget option.
More pullers and presses are under tools. For the transmission itself, CoreTransmissionParts.com carries rebuild kits and hard parts.
Match the Splines, Match the Series
27-spline GM, 30-spline Chrysler and 31-spline Ford slip yokes in 1350 series, plus a flange adapter for late GM transmissions. Count twice, measure your joint, then order once.
GM 27-Spline Yoke → Ford C6 31-Spline 6L80/8L90/10L80 AdapterFAQ
How do I tell a 1310 from a 1330 U-joint?
Both use 1.062 inch caps, so cap diameter will not separate them. Measure across the caps: a 1310 is about 3.219 inches wide and a 1330 is about 3.625 inches.
Does a TH350 slip yoke fit a 700R4 or 4L60E?
They share the 27-spline output, so the splines match. Barrel length and extension housing length can differ between applications, so confirm the yoke engagement and seal surface position before you drive it.
Is a chromoly slip yoke worth it on a stock engine?
Usually not. A good forged yoke is plenty for stock power. Chromoly earns its price with power adders, trans brakes, hard launches and heavy towing.
Should I replace the tailshaft bushing with a new slip yoke?
If the old yoke was worn, scored or leaking, yes. A worn bushing lets the new yoke wobble, which destroys the new seal and can cause vibration.