What You Need To Know About Street & Strip Driveshafts Part 1

This is an SFI certified driveshaft. Essentially the 43.1 spec means applying a 2,500 lb. load, reversing it to 1,000 lbs., and performing 25 such cycles at a rate of at least 3-5 cycles per minute. Any torsional angular deformation of the shaft is subject to certification disqualification. So are signs of buckling or cracks. Williams’ shafts routinely exceed these parameters on a regular basis.
Driveshaft How-To

Mark Williams helps Wayne Scraba understand the technology and materials that go into high performance driveshafts in Part 1 of a three part series.

Not so long ago, it was common practice to get a driveshaft built or modified by a local big truck driveline shop. Typically, they had the capability to cut and weld or modify a driveshaft and if you’re lucky, properly balance it. Many a time that custom shaft was simply a piece designed for a truck and modified.  Some folks still do this today, but there’s a catch:

Technology has barreled forward, even when it comes to the humble driveshaft (you know – the thing that’s out of sight, out of mind). While some local shops can fabricate driveshafts out of aluminum or steel, many don’t have the capability to work with more exotic materials (for example, carbon fiber or 7075 aluminum).  Many cannot provide high strength yokes for larger than stock universal joints.  Some won’t tell you the type of material used in the manufacture of their driveshafts.  That’s important, because material type and dimensions influence the critical speed of the driveshaft.  We’ll get to critical speed later, but right now, let’s look at various materials used in high performance and race driveshaft construction.  Thanks to Mark Williams we have some very deep insight everything related to driveshafts.

According to Mark Williams, “The first thing to take into account is the strength of the driveshaft a racer will need. The more power you have and the more a car weighs, the stronger the driveshaft needs to be. The weight of the car is one factor that is often forgotten when selecting a driveshaft. A 4000 lb. car with 1000 hp will be much harder on a driveshaft than an 1800 lb. car with the same power. There are three factors that make a driveshaft strong — material, diameter, and u-joint size.

“In terms of material, steel and thicker walls will be the strongest choice, although there are obvious drawbacks with the added weight. Using high strength alloys allows thinner tubing walls to take out extra weight without sacrificing strength. Aluminum, especially when using high quality 7075 tubing and ends, offers a well balanced mix of strength and weight. Carbon fiber is by far the lightest driveshaft material with good strength. Mark Williams Enterprises offers a large array of material choices including: Mild steel, 4130 chrome-moly, 6061 aluminum, 7075 aluminum and carbon fiber.

“Increasing diameter will significantly increase the strength of a driveshaft, no matter the material. For example, increasing diameter from 3″ to 4″ will increase strength by about 80%. Increased diameter has some other benefits that we will discuss later.

“The two most common u-joints used in drag racing are the 1350 and 1480 series u-joints, both offered by M-W. For the most part, 1350 series u-joints will work in almost every situation. They offer the best mix of strength, precision and weight. They are used in every class all the way to pro-stock. 1480 joints are reserved for extra heavy duty applications, mainly used in Pro-Mod and other high power classes especially when tire shake is an issue. U-joints are usually the weakest piece in the system.”

Mark Williams offers a huge range of high performance and racing driveshaft options (few, if any other companies have choices this wide). Include in the mix of conventional driveshafts are those below. Keep in mind M-W also offers specialized shafts for all sorts of different applications. See their website (www.markwilliams.com) for more info.  Conventional driveshafts are available in almost any length.

Here’s the conventional shaft mix from M-W

Mild Steel:  Three different outside diameters are available – 3-inches, 3.5-inches and 4-inches.  Two different wall thicknesses are available for each shaft – 0.065-inch or 0.083-inch.  All of the shafts include Spicer 1350 non-greaseable, lubed for life universal joints.

Chrome Moly Steel:  Williams offers these 4130 steel shafts with two different outside diameters  (3-inches  and 3.5-inches). Both have a wall thickness of 0.083-inches.  Two of the shafts are designed for 1350 style Spicer universal joints, while the other makes use of huge 1480-series Spicer u-joints. Mark Williams tells us that in terms of strength, their Chrome Moly steel shaft is the strongest they build:

“A chrome moly shaft is 75% stronger than commonly used 1020 DOM material. To ensure the quality of the material, the heat treated tubing used is manufactured to MW’s stringent specifications. The perfect companions to MW’s chrome moly tubing are the MW produced, 4130 forged weld yokes  used in each assembly. These weld yokes are produced in-house to exacting tolerances to provide the proper press fit in the chromoly tube. Precise alignment, or “phasing”, of the weld yokes is critical to smooth operation. Spicer forged weld yokes and chromoly tubing are assembled using a specially built alignment / assembly fixture, then carefully joined using an automated cold wire TIG process. MW’s exclusive 1350 series precision u-joints are then installed along with the forged 4340 heat treated transmission yoke (sold separately). Each assembly is high-speed electronically spun and balanced at an RPM that represents operating speed (to G30 industry tolerances). The finished product is a driveline capable of handling today’s most powerful vehicles. Prices are less transmission yoke. All 4130 chromoly driveshafts meet SFI spec 43.1.”

6061 Aluminum:  When it comes to 6061 driveshafts, M-W offers two different outside diameters in their Master Line product mix.  These shafts are manufactured with either 3.5-inch or 4-inch OD 6061 material with a 0.125-inch wall thickness.  A billet steel transmission yoke (of your choice) is included. Both driveshafts are manufactured with lubed for life Spicer universal joints.  Williams incorporates a special assembly fixture to ensure proper yoke phasing during the welding operation.  Like all M-W driveshafts, the 6061 aluminum line up models are electronically high speed balanced considering with the transmission yoke to ensure vibration-free operation.

7075 Aluminum:  M-W offers 7075 alloy aluminum driveshafts in two different outside diameters (3.5 and 4.0-inches), one wall thickness (0.110-inch) and two different universal joint configurations (1350 and 1480 series u-joints).  M-W also offers 7075 alloy shafts for Hellcat and several different Mustang applications. All of the standard shafts are manufactured with 7075 alloy tubing along with forged 7075 alloy yokes.  Williams notes that 7075 material is approximately twice as strong as 6061, but unfortunately, 7075 alloy cannot be welded by conventional means. Since it cannot be easily welded M-W invented a patented process that physically bonds (Accu-Bond) the yokes to the shaft tubing.  And since 7075 is significantly stronger than 6061, this has allowed Mark Williams to reduce the wall thickness of the tubing used in the shaft.  Williams tells us the thinner wall section allows for a lighter drive shaft along with higher maximum operating RPM when compared to conventional aluminum and steel counterparts. The bonding process actually improves the strength of the shaft. That’s why 7075 alloy shafts with 1480 series universal joints (and yokes) are widely used in Pro Mod applications.  We’ll discuss why reducing driveshaft weight is important later.

Williams also notes there is a considerable strength advantage with a bonded driveshaft versus a welded shaft.  As it turns out, welded shafts will always have a weak spot surrounding the weld where the heat from welding affects the heat treat of the aluminum.

Carbon Fiber:  Mark Williams offers carbon fiber shafts with one outside wall diameter and one wall thickness – 4-inches in diameter X 0.150-inch wall thickness.  The end yokes used in the carbon fiber shafts are forged from 7075 material, and like the 7075 shafts, the carbon fiber examples are assembled using Williams’ Accu-Bond process.  These shafts are built with Spicer 1350 series “lubed for life”, non-greaseable universal joints.  Typically, carbon fiber driveshafts are used where engine speed is high, power is less and/or where the driveshaft length can prove long (critical shaft speed becoming an issue).  An example of a car that can really make use a carbon fiber shaft is something like a Tri Five Chevy with a high RPM small block (think NHRA Super Stock ’55-57 Chevy with dual carburetors and a Powerglide). Here, we have a very high RPM, low torque application coupled with a rather long driveshaft. This combination results in a shaft with high critical driveshaft speed – something we’ll address further on in this series.

Next time around, we’ll look at universal joints (and boy, there are certainly differences between them), along with driveshaft weight and balance.  You might be surprised at the info provided.  Meanwhile, check out the accompanying photos for a closer look at a Mark Williams’ 7075 alloy driveshaft:

When you think of a driveshaft, this is what often comes to mind – a rusty, battle-worn hulk of a shaft that has most likely seen better days. It should be no secret this isn’t the path to performance. The Mark Williams’ shaft shown in the opening photo is more like it.

 

As noted in the text, M-W manufactures all sorts of different driveshafts. This is one of their exclusives – a 7075 alloy shaft complete with custom 1350 yokes and bonded construction.

 

When complete, the Mark Williams bonded shaft arrangement makes for one of the strongest driveshafts possible. There are no welds and because of that, there is no weak spot surrounding the weld where the heat from welding affects the heat treat of the aluminum.

 

This is an SFI certified driveshaft. Essentially the 43.1 spec means applying a 2,500 lb. load, reversing it to 1,000 lbs., and performing 25 such cycles at a rate of at least 3-5 cycles per minute. Any torsional angular deformation of the shaft is subject to certification disqualification. So are signs of buckling or cracks. Williams’ shafts routinely exceed these parameters on a regular basis.