May - June 2000 Motor State Performnace Report Article By Jim Kaekel, Jr.
Imagine traveling at 100 miles an hour on a dragstrip or a circle track when the car ahead has decided it's time to shuck its driveshaft. A four foot long, three inch diameter metal tube headed toward the windshield, especially at these speeds, is enough to make a pagan join the 700 Club. Driveshafts are taken for granted until a failure occurs, then questions quickly arise. Was it a U-joint failure? A yoke? Or the shaft itself?
Here are some informational tidbits about driveshafts, their function, and their selection. Keep in mind that proper driveshaft selection relies on several important factors including weight, material, center-to-center length of the yokes, car weight, engine power, RPM range, and length of the shaft.
The driveshaft transfers the power from the transmission to the rear end and has been manufactured for decades from mild steel. In the past fifteen years, driveshaft evolution has been rapid and shafts are now routinely built of aluminum and even space age carbon fiber. Many rear-wheel drive passenger cars and light duty trucks now come from the factory with aluminum driveshafts because the manufacturers realize that, in addition to weight savings, it takes less horsepower to achieve the same rate of acceleration when the shaft is lighter.
Aluminum shafts are offered in two varieties: 6061-T6 and Duralcan. Duralcan aluminum has a special ingredient that increases strength by another 28% over standard 6061-T6. According to Matt Dotson of Mark Williams Enterprises, an aluminum driveshaft can be as much as 60% lighter than its steel counterpart. Aluminum shafts are popular among Pro Stock drag cars and trucks (Pro Stock trucks use a 4" diameter Duralcan shaft because of their longer wheelbases) as well as Limited Late Model and Late Model circle track cars. Even some well-financed Factory Stock cars have benefited from the use of an aluminum driveshaft.
Carbon fiber driveshafts, now available from Trick Race Parts (see previous page) have gained wide acceptance among circle track racers, especially those who race Dirt Late Models. A 40" Trick Race Parts carbon fiber shaft weighs just 5 lbs., compared to 9 lbs. for a similarly sized aluminum shaft. Trick is currently developing a 3" diameter carbon fiber shaft that will accept 1350 Series U-joints and be suitable for use in Trans-Am and drag racing.
Stephen Lefrance of Trick Race Parts states, "...carbon fiber shafts have been extensively tested by several Hav-A-Tampa Series racers and have proven to be very successful." He added, "Sales have been phenomenal!"
A vehicle's driveshaft center-to-center length is not really a matter of choice, but a short driveshaft is less prone to failure than a long one because as engine speed increases, the longer driveshaft has a tendency to "whip.", causing structural weakening. Therefore, it would be safe to say that a longer driveshaft should be made of larger diameter, heavier wall, tubing for added strength (even though it will weigh more).
When ordering a driveshaft, keep in mind that yokes and U-joints are very important parts of the package. Universal joints are available in 1310, 1330 and 1350 series, with the 1310 being the smallest and 1350 the largest.
The 1310 series is popular on circle track cars, while 1350 series is most often used on drag race cars, in conjunction with heavy duty transmission and pinion yokes (especially on heavier, full-bodied cars). The 1350 series U-joints are a full 3-5/8" wide and have very large 1-3/16" bearing cups. 1350 U-joints are also available less grease fittings, making the joint completely solid and considerably stronger. Mark Williams Enterprises has a full selection of U-joints and billet steel yokes available for most popular transmissions and rear ends.
Take some time, select the right driveshaft for that particular application, install it and there will be one less worry come race time. Please pass this information along to your customers and fellow racers, too, because no one really wants, or needs, to endure that significant emotional experience of the "flying driveshaft" that we mentioned in the opening paragraph!