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Driveshaft Science

Propelling technology for project cars

What do hot rodders, customized car builders, race shops and automobile restorers have in common? They all need to build custom-length driveshafts from time to time. Many project-car builders need specialized driveshafts if the part is out of production, or when mixing and matching oddball engine and transmission combos with non-standard chassis lengths. This also holds true for a front-engine project car with a shortened or lengthened chassis. Although you may get lucky and find a standard-length driveshaft that will fit, it is not likely to accept the heavy-duty larger-diameter U-joints that may be required to handle the power of high-performance engine upgrades.

Driveshaft Shopping

To see what is involved in building a custom driveshaft, we had one made up for a sports car in need of a shaft to join a Chevy small-block V-8 with a Borg-Warner T-10 tranny to a custom-built DeDion rear end (a type of independent rear suspension). When shopping for a driveshaft, be sure to choose a company with custom shaft experience. The good news is that custom steel driveshafts are not that expensive, generally running under $200 (if you require aluminum or carbon fiber, expect to pay more).

If you have a good driveshaft you will never notice it, but a bad one will be a nightmare. Vibration from an incorrectly balanced or assembled shaft will result in annoying noise and short U-joint life. Although anyone with a hacksaw and a welder can assemble a shaft, getting one right requires experience and professional equipment.

U-Joint Basics

There are three basic sizes of U-joints: 1310 (approx. 3-1/4" wide with 1-1/16" or 1-1/8" diameter caps), 1330 (3-5/8" wide with 1-1/16" or 1-1/8" caps) and 1350 (3-5/8" side with 1-3/16" caps). The 1350 is also thicker than the other two and is recommended for racing cars producing more than 400 hp. For high performance you will want heavy-duty U-joints, and for racing you need ones without grease fittings (which weaken the joint).

You can mix U-joint sizes at each end of the shaft but the strength will be limited to that of the weaker joint. A used driveshaft can be cut down, but only if it is in perfect condition (damaged shafts should not be repaired). When you assemble the joints onto the pinion yoke, torque the nuts to 17 lb.-ft. on 1310 and 1330 joints, and 20 lb.-ft. on 1350 series joints. Don't exceed these recommended specs because over-tightening can lead to premature wear. View the detailed steps in the Photo Gallery.