Custom Ford Driveshafts For Increased Power - Shaft

Driveshafts just don't give us that eye washing thrill of a powerful new engine, a fresh coat of paint, or a striking set of wheels. But they're just as important as horsepower, paint, and rolling stock. We don't give driveshafts much thought when we're planning our projects. And unless the driveshaft or a universal joint fails, it just isn't going to get much of our attention.

It's good practice to think about the driveshaft and universal joints when you're planning more power underhood. As horsepower and torque increase, the demands on a driveshaft, universal joints, and yokes rise accordingly. If you are stepping up to a 9-inch rearend, the difference in driveshaft length is probably going to mandate a new driveshaft anyway.

How do you order a new driveshaft, and what do you need to know before doing so? Before we get into driveshaft fabrication, let's look at driveshafts, universal joints, and yokes.

Driveshafts
There are three basic types of driveshafts available for classic Fords: steel, aluminum, and carbon fiber (composite). Classic Fords and Mercs were fitted with steel driveshafts from the factory. Some were of a two-piece design, with an outer shaft and an inner shaft separated by a rubber vibration absorber. This design was common with automatic transmission cars to improve driveline smoothness. Manual transmissions were a single steel tube shaft only. Some applications were fitted with a slip-yoke/harmonic balancer design, also intended to absorb vibration. There were many variations in vintage Fords to begin with.

In any case, be it one-piece steel or two-piece, we suggest replacement of your factory driveshaft with a new one-piece steel shaft for your vintage Ford. We make this suggestion not to help these folks sell driveshafts, but for you to get into current universal joint technology, availability, and installation. Many original Ford driveshafts use inside snap-ring universal joint cup retainers. These clips have been known to fly out (if improperly installed), causing the cup to fly out, which throws the driveshaft off center. If this happens at 70 mph, it can be catastrophic. When a driveline company builds you a new shaft, it uses the outside snap ring cup retainers, which are more secure and safer. But like the inside snap ring, they mandate close attention to detail during assembly. Another issue surrounding the inside snap-ring universal joint is availability. They are harder to get these days from auto parts stores for classic-style driveshafts.

We visited Inland Empire Driveline for this story, and when Inland Empire Driveline builds a new shaft, you get new universal joints and a new slip-yoke, which eliminates all worn out parts. With the driveshaft come other issues that need your attention if everything is to work smoothly. Replace the transmission tailshaft sleeve bushing and tailshaft seal, which improves fit around the new slip-yoke, getting everything back in proper tolerances for driveline smoothness.

In the '90s, aluminum driveshafts started showing up in new Fords, as well as the automotive aftermarket. Aluminum driveshafts offer us reduced weight and less rotating mass than steel. They are not tolerant of extremes of torque. They twist and break when we exceed their design limits. Aluminum driveshafts call for the use of special universal joints with coated caps designed to prevent dissimilar metal corrosion that comes when steel and aluminum make contact with each other. Aluminum driveshafts are also subject to distortion and irregularities we don't normally see with steel driveshafts. This calls for extraordinary attention to detail during manufacture. Inland Empire Driveline features custom-made aluminum driveshafts in 6061-T6 aluminum for strength. What's more, each shaft is state-of-the-art welded for consistency and strength, passing Spicer's reverse-torsion testing. This makes Inland Empire Driveline an authorized Spicer driveshaft builder.

Composite or carbon-fiber driveshafts are featherweights, the lightest driveshaft you can buy. They are also the strongest. Composite shafts offer unprecedented strength coupled with lightweight construction, making them perfect for high-stress applications that could break a steel or aluminum shaft. The composite shaft is designed to tolerate 3,900 lb-ft of torque. Rotation is smooth and stable up to 14,000 rpm. Composite driveshafts are common in late-model GM cars, such as the Camaro and Firebird, where composite material is wrapped around the aluminum shaft. Composite driveshafts are available from Inland Empire Driveline on a made-to-order basis. They are not an off-the-shelf item and do not come inexpensively. Where off-the-shelf steel and aluminum shafts cost anywhere from $350 to $500 each, a composite shaft for the same application can run upwards of $1,000. That's the price you pay for solid driveline integrity when you are going racing.

If you want to reduce rotating weight, composite driveshafts make sense. Unless you want your street Ford to be decidedly different than the rest, and are willing to pay the price, you do not need a composite driveshaft for your street warrior. If you just have to have one, be prepared to pay the price.

When you are ordering a driveshaft, expected power output is very important to know. Most applications will live happily with a 3-inch tube. When you are going to pump greater than 500 hp through the shaft, you're going to need a 3.5-inch shaft with larger universal joints and yokes.

Universally Speaking
Universal joints are installed at each end of the driveshaft to allow the shaft to articulate with the rear axle. These little guys have a big job to do. They have to keep power going to the rear axle under some very adverse conditions. The more power we throw at the driveshaft and universal joints, the larger and beefier these items have to be.

Most Ford applications call for a Spicer 1310 universal joint at each end of the shaft. The 1310 vary according to cap size, meaning being able to tie the driveshaft to different applications. Most original Ford applications call for an inside clip universal joint that is numbered differently from the 1310. Your local Spicer dealer or Inland Empire Driveline will have the necessary information if you choose to rebuild your original driveshaft. If you're stepping up to more power, you will want to consider the 1330 or 1350, which are larger universal joints for more heavy-duty applications.

When we speak of 1310, 1330, and 1350 universal joints, we are talking about the basic joint body with each number without the caps. A basic 1310, for example, has the same size cap on all four sides: 1.063 inches. The same is true for the 1330: a larger universal joint, also with 1.063-inch caps in on all four sides. The 1350 joint is a super heavy-duty piece with 1.188-inch caps.

When we go with different cap sizes on the basic 1310, 1330, or 1350, we are then dealing with a conversion universal joint. For example, you want to install a 9-inch rearend in your Mustang with an 8-inch rearend. If driveshaft length works out, or you are able to go with a different yoke, all you need is a conversion 1310 with the correct 1.125- or 1.075-inch caps opposite the 1310's native 1.063-inch caps. With an 8-inch rearend, we would have the smaller 1.063-inch caps on all four sides.

Yokes
Driveline yokes present their own set of challenges because there are several variations. It is up to the informed enthusiast to choose the right one. The slip-yoke slides back and forth at the transmission's tailshaft, hence the name. There are two basic slip-yoke types (although there are many variations of the two types): 28-spline for small-block transmissions such as the C4, Top Loader, T-10, and T5; the 32-spline (larger) for big-block applications such as the C6, big-block Top Loader, T45 (if you're running a Modular V-8), and Super T10. The factory slip-yokes are made of cast iron and machined steel alloy.

When you are pumping up the power, you're going to need more yoke and the corresponding universal joint. When horsepower rises above 500, a 1310 joint will not stand up to the torque. And because we like to see a measure of safety demonstrated here, we suggest stepping up to a 1330 or 1350 when horsepower goes above 400. With this kind of increase in power, we suggest going with one of Inland Empire's CNC machined, heat-treated forgings with the quick-release cap design for easy maintenance. These 1350 Quick Release yokes will withstand brutal amounts of power. If you are planning huge gains in power, you will want this yoke, along with 1350 joints.

Inland Empire Driveline offers a couple of differential pinion yokes for high-performance Ford applications. The 1350 steel pinion yoke, like the 1350 Quick Release, is designed to take a lot of punishment. a 7075 T-6 aluminum pinion yoke (1310 and 1350) is also available.

When you study the slip-yoke and pinion-yoke part numbers, choose your yoke based on the transmission type, differential type, and the universal joint you intend to use. The universal joint number is incorporated into the yoke part number. So is your transmission type.

Let's Build A Driveshaft
When you walk into Inland Empire Driveline or Mustangs Plus to buy a driveshaft, you can count on the shaft being an "in-stock" item if you are building a commonplace driveline package. Shafts are available in stock for applications such as a '67 Mustang with a 289, C4 Select-Shift, and an 8-inch rearend. If you are building something out of the ordinary, such as a 5.0L EFI small-block, Tremec TKO, and a 9-inch rearend, you will have to order the shaft. Inland Empire Driveline can build a driveshaft to your specifications and have it on your doorstep in a matter of days.

We decided to have Inland Empire Driveline build us two driveshafts for our project cars: one steel, one aluminum. We learned there isn't much difference in price with steel and aluminum, both are competitively priced.