The rub marks on this shaft...
The rub marks on this shaft indicate steady contact with a rubber belt or hose. Even soft materials can quickly overheat the tubing and ruin the driveshaft. The driveshaft must be considered an expendable part and replaced immediately if such damage occurs.
Regularly inspect the driveshaft for any indication of contact or rubbing against any part of the car. The most common culprit is a spare rearend V-belt or a loose brake duct. The friction and heat from such rubbing can wear a groove on the tube like a lathe parting tool, rendering the shaft unusable.
Hardened slip-yokes can easily outlive a given shaft and are routinely recycled onto new shafts at the professional level. But even a hardened slip-yoke can be ruined by inadequate lubrication or localized heating. A broken header can overheat a U-joint and destroy its seals. Post-race chassis dyno runs can deprive the yoke of lubrication. Any slip-yoke or U-joint that has been visibly overheated should be removed from service.
If you suspect a driveshaft vibration, unbolt the shaft at the pinion and rotate it 180 degrees and re-install it to see if the driver notices a difference. Having a good spare shaft to try next can quickly isolate a vibration problem as being driveshaft related or not.
17. Driveshaft Maintenance
As we mentioned before, your driveshaft is a precision piece of racing equipment that will give good service life if you treat it right. This includes keeping records on its usage and periodic inspections. The U-joints are sealed for life and require no cleaning or regreasing. Clean the shaft thoroughly, removing any built-up rubber or surface grease, and then lubricate the exposed machined surfaces with WD-40 or a light grease to prevent rust in storage.
NASCAR teams often mark their...
NASCAR teams often mark their driveshafts after each use so they can quickly determine the accumulated stress that the shaft has endured. A notebook like this is hard to put in your pocket, but racers have developed simple systems like these to prevent shafts from being used beyond their safe projected life.
A racing driveshaft has a usable life that can be measured in miles, hours, or seasons. For sustained high-rpm NASCAR applications, a team wouldn't consider running a shaft beyond five full 500-mile race events. This means the shaft has (including practice) over 3,000 miles or 30 hours of on-track use. This would be the equivalent of a season of lower-rpm short-track activity.
The top teams keep careful usage records of each shaft and can determine exactly how many miles each shaft has seen. As miles accumulate, the shaft may be retired from primary competition and assigned to a back-up car or testing activity only. At the end of its usable life, the shaft will be destroyed or sold, or the hardened slip-yoke will be harvested so it can be assembled onto a new shaft. A quick way to monitor use is to mark each activity on the tube, like notches on a gun. This gives an easy visual reference to the total time on the shaft.
19. Shop Repairs Vs. Manufacturer Repairs
While a racing driveshaft looks like an easy assembly to tear down and rebuild on your bench, you should leave all such repairs to the manufacturer. It is best equipped to inspect the shaft and its components closely, replace the parts subject to wear with the correct parts, and reassemble the shaft correctly. Any shaft that has had any component replaced must be rebalanced. Current high-speed balancing techniques are so precise that any change to a shaft's components will destroy the initial balance.
A racing driveshaft should be balanced on a quality high-speed balancer by an experienced operator. Few modern cars use a conventional driveshaft anymore. The heavily used balancer at your local heavy truck drivetrain shop does not have the rpm capability nor the precision to properly balance a lightweight racing driveshaft. No matter how carefully the people at the shop try to balance the shaft at a lower speed, the dynamics of the shaft at high speed will be dramatically different.
Thanks to the efforts of the manufacturers' and teams' drivetrain specialists, the modern racing driveshaft is seldom seen on national television broadcasts and never discussed in public to the level of detail that we have now covered. Every racing car owner, crew chief, mechanic, and driver should be made aware of the critical role the driveshaft plays in car performance and safety.
This precision piece of equipment and its environment must be carefully specified and regularly inspected. The driveshaft should be considered an expendable part and replaced immediately if its condition is in doubt.
Any driveshaft failure on race day will ruin the efforts of your team. The resulting damage may render your race car unrepairable. A catastrophic crash will put the driver, other competitors, the fans in the stands, and even the entire sport in jeopardy.
Far more than being a simple connector or an afterthought, the racing driveshaft is a mission-critical link to the success of your team. Take it for granted and you will surely fail. Specify it correctly, treat it with the respect it deserves, and you will graduate to Victory Lane and Driveshaft 201.