The transmission manufacturer can install a simple bronze bushing as the wear surface or, as an option, have the housing machined for use of a double-roller bearing setup to reduce internal friction. It's important that you know which design you have to make the correct slip-yoke choice. Ask your transmission supplier which system he uses or visually inspect behind the tailshaft seal for a bushing or bearings.

The conventional non-hardened cast or forged slip-yoke is well suited for use with a bushing in the transmission tailhousing. But it will quickly fail when used with a roller bearing. The roller bearing setup utilizes the barrel of the slip-yoke as the inner race of the assembly, and the barrel must be hardened to match the rollers or they will rapidly wear a groove into the barrel.

High-quality hardened billet steel slip-yokes from Mark Williams Enterprises or C&R Racing are the best choice when using a tailshaft roller bearing. These precision parts come at a higher price but will typically outlive a given shaft. NASCAR teams routinely harvest billet yokes from older shafts to build them into fresh ones.

There are varying opinions on the need for venting the slip-yoke for smooth travel. Some manufacturers machine one or two of the splines to act as a channel for trapped air to escape as the slip-yoke moves in and out.

The original production reason for the missing spline was to speed up car assembly by allowing the stock driveshaft to be quickly shoved into place. The racing driveshaft, on the other hand, will travel very little in normal use, and venting is not a big problem as air can find its way past the array of splines.

It is important that your driveshaft U-joint series choice be matched by the specification of the pinion yoke on your rear gear. Any mismatch between the front and the rear of the shaft means that the smaller U-joint becomes a potential fuse, which will inevitably break first.

We have more information coming next month about racing driveshafts. Make sure you choose the correct driveshaft for your particular application. If in doubt, contact your supplier, ask a lot of questions, and provide the needed information. Your success and race car's reliability depend on it.

Your new engine has just arrived and you realize that you need a new driveshaft now! Bob Gosch, of Rapid Response in Mooresville, North Carolina, is a driveshaft specialist. He has worked for 30 years within all kinds of motorsports. He has been the operations manager for numerous racing-related companies and technical director of the International Motor Sports Association.

Bob's company supplies many NASCAR and other series' teams with specialized racing driveshafts. He can normally deliver a new racing driveshaft from Rapid's extensive inventory to a team very quickly. Many NASCAR teams count on Rapid Response as their inventory partner to deliver shafts for their specific requirements on a "just-in-time" basis.

"We typically ask three simple questions to fit the correct shaft, but the customer has to be ready with the answers to get it right," Bob says.

1."What series do you race in?" This determines the material, diameter, thickness, and U-joints needed.

2. "Does your transmission have roller bearings in the tailshaft housing?" The roller bearings require a hardened billet slip-yoke.

3. "What is your length?" Racing driveshafts are specified by the length from the center of the front U-joint to the center of the rear in 11/44-inch steps.

Armed with these answers, Rapid Response can get you going. As Bob says, "You can get a custom Dynotech driveshaft in Mooresville faster than you can get a pizza!"

Rapid Response