LS swap driveshaft and driveline angles

How we put this guide together

Of the 2,012 LS swap questions we pulled from forum threads, 91 were about the driveshaft, the crossmember, pinion angle or the slip yoke. Most were asked after the fact: a vibration at 60 mph, a transmission sitting too low, a shaft that bottoms out, a yoke that doesn't fit. All of them come from two things a swap changes, the length of the shaft and the angles it runs at. Here is how to get both right the first time.

Step 1: Understand why the shaft changes

Three things move the front of the driveshaft in a swap:

• The transmission is a different length. A 700R4 is about 30-3/4 in overall, a TH350 with the long tailhousing about the same, a short-tail TH350 much shorter. An LS-style 4L60E is 31-5/32 in, a 4L80E is longer again, and a T56 is different from all of them. Even a "same length" swap usually moves the mount pad: a 700R4's sits farther back than a TH350's, so the crossmember moves about 1-3/8 in.
• The engine position moves. Swap mounts can put the engine 3 in forward (Tejas plates on a squarebody) or 3.5–4 in back (a Nova with the crossmember slid back). The transmission moves with it, and the shaft gets shorter or longer by the same amount.
• The crossmember sets the height. A transmission that sits lower or higher than stock changes the angle of the whole driveline, not just the length.

Some kits keep the stock position on purpose. ICT's G-body and C10 mounts, and Hooker's 12621HKR brackets on a 1983–87 truck with a 4L60, keep the factory crank and bellhousing location, so the stock shaft and angle carry over. Most others need a new shaft. More: engine mounts and swap kits.

Step 2: Get the angles right

A U-joint doesn't turn at a steady speed when it runs at an angle: it speeds up and slows down twice every turn. Two joints cancel each other out only when their working angles match. That's the whole job.

• Engine and transmission tilt down at the back. Most rear-drive cars and trucks set the crank centerline about 3° down toward the rear. Hooker's swap systems are drawn for 3 to 3.5°. That's the reference everything else is set against.
• The pinion points back up the same amount, so the pinion centerline is parallel to the crank centerline. The shaft runs between them, and each U-joint's working angle (the difference between the shaft and the yoke it connects to) comes out the same.
• Keep the front and rear working angles within about 1/2° of each other (1° at the very most). That's the number that matters most.
• Keep each working angle small but not zero. At least 1/2° and no more than 3° on a street car. Zero means the needle bearings never roll and wear in one spot; past 3° costs U-joint life and brings vibration at highway speed. A two-piece shaft keeps every joint at 3° or less.
• Leaf springs wind up. Under power the axle housing rotates and the pinion climbs. On leaf-spring cars and trucks, many builders set the pinion a little lower than parallel at rest so it comes up to parallel under load. Link suspensions move far less.

How to measure:

1. Put the car at ride height with weight on the tires: on a drive-on lift, on ramps, or with stands under the axle. Never with the suspension hanging.
2. Use an angle finder that reads to 1/4° on a machined surface. Turn the shaft so a U-joint cap points straight down and read the flat machined ear of the front yoke, then the driveshaft tube, then the flat on the pinion yoke (or the face of the pinion flange).
3. Write the three numbers down with their direction (front down or front up). The working angle at each end is the difference between the shaft and that yoke.

How to fix it:

• Front angle: shim under the transmission mount, or move to a crossmember with a different height. Shim upward to raise the tail, never by lowering the mount. Check the mount hasn't collapsed first.
• Rear angle: tapered shims between the leaf spring and the axle perch, or adjust the upper links equally on a 4-link. A torque-arm car (3rd-gen F-body) sets it with the torque arm mount.
• Recheck after any change to mounts, crossmember or ride height. A lowered car changes all three numbers.

Step 3: Measure for length

Only after the engine, transmission and crossmember are bolted in their final spots:

1. Car at ride height, weight on the tires.
2. Measure from the seal surface at the back of the transmission tailshaft housing (not the end of the output shaft, which makes the number short)…
3. …to the center of the rear U-joint (the flat face of the rear yoke or flange).
4. Give that one number to the shaft builder with your transmission, yoke spline, rear U-joint size, horsepower and top rpm.

The slip yoke needs room to move both ways. The usual rule: push it all the way into the transmission, pull it back out 3/4 in to 1 in, and measure from there (U-joint center to U-joint center if your builder asks for it that way). In far enough to stay supported, out far enough that it never bottoms when the axle moves up. A shaft that's too long bottoms the slip yoke and can crack the transmission case or push the converter into the crank; one that's too short pulls the yoke off the output shaft splines. If you're cutting a donor shaft at a local shop, ask them to check engagement with the yoke seated at ride height.

Step 4: Pick the slip yoke for your transmission

Front slip yoke	Transmissions
GM 27-spline (1.5 in seal)	TH350, Powerglide, 700R4, 200-4R, 4L60, 4L60E, 4L65E, 4L70E, Muncie, Saginaw, T-5, T-10, F-body/GTO T56
GM 32-spline	TH400 (no threaded hole in the output shaft), Muncie M22, Super T10, 4L80E, 4L85E
31-spline (Ford C6 style)	Tremec TKO, TKX, T-56 Magnum, Magnum-F, TR-6060

Check the transmission you actually have. T56s differ by the car they came from (F-body 27-spline, Viper 30-spline), and TR-6060 output fitments vary by application. On a 4L80E going in where a 4L60E was, everything changes: yoke, length and crossmember.

The rear end needs matching attention: count pinion splines and know the U-joint series (1310, 1330, 1350) or flange (BMW, Nissan, Toyota and Ford 8.8 differ). Conversion U-joints join two different series when the yokes don't match. One-piece shafts in imports (E36, E46, 240SX, 350Z, 86) replace the factory two-piece shaft and its center bearing.

Step 5: Pick the tube for your power and length

Two limits decide the tube: torque (horsepower and how hard you launch) and critical speed, the rpm where a shaft whips at its natural frequency. Longer shafts reach it at a lower rpm; a bigger diameter and a stiffer, lighter material raise it. That's why a longer shaft usually needs a bigger tube.

Tube and joints	Typical use
2.5 in steel, 1310 joints	Street cars under about 400 hp, shafts up to about 50 in
3 in steel or 3.5 in aluminum, 1310 joints	Street cars under about 500 hp; 3 in steel up to about 55 in
1330 joints	About 700 hp in a car around 3,200 lb
3.5 in steel, 1350 joints	Big power: up to about 1,200 hp, up to about 66 in
Carbon fiber, 1350 joints	Rated up to about 2,000 hp; the highest critical speed

The 1350 joint works in almost any street or strip LS swap. Critical speed falls fast with length: a 3 in mild steel tube whips at about 7,900 rpm at 44 in long but about 4,200 rpm at 60 in, while a 4 in carbon tube is still above 7,500 rpm at 60 in. Driveshaft rpm is engine rpm divided by the overdrive ratio, so a 0.50 sixth gear spins the shaft twice as fast as the engine.

A truck's long single shaft, a lowered car with a high-rpm cam, and anything over 500 hp are the cases to talk through with the builder. Have the shaft balanced; a shortened donor shaft needs it too.

Common mistakes

• Measuring with the suspension hanging. The length and every angle change at ride height.
• Buying the shaft before the crossmember is final. Mock it all up first, then measure.
• Zero working angle on a perfectly straight line. The U-joints wear out from the needles never turning.
• Matching the angles to each other but not to the crank. Measure the transmission, the shaft and the pinion, not just two of them.
• Shimming the transmission down to fix an angle. Raise the other end or change the crossmember.
• The wrong yoke spline. A 4L80E and a 4L60E don't share a yoke, and a TH400 yoke fits a 4L80E only if the output shaft has no threaded hole.
• Ignoring vibration. A vibration that comes in at one speed is the driveline telling you an angle or the balance is off. Find it before it takes out the transmission seal or a U-joint.

Find your vehicle in the table below for the crossmembers and shafts we know of, and what changes on each.