Start talking about universal joints, and the common man's eyes glaze over. For us 'wheelers, however, the constantly evolving world of the U-joint is fodder for hours of conversation and debate. Heck, we'll admit to getting downright giddy on the subject from time to time.
Well, now we have something new to talk about. Tom Wood's Custom Drive Shafts has recently thrown an interesting new U-joint into the mix with the introduction of the Super-Flex universal joint. Wood says that this new joint was designed in collaboration with rockcrawler Chris Durham and put into production by the company. This joint is designed to solve binding issues in certain situations. A couple of examples are a front CV driveshaft that is binding at the axle due to extreme driveshaft angles, or a rear CV driveshaft that is suffering binding at the axle due to spring-wrap issues resulting from a spring-over axle conversion. Wood does not recommend using the joint in a standard two-joint driveshaft because its offset trunnion design creates too much vibration.
We hung out while Attitude Performance in Arlington Heights, Illinois, installed one of these joints in a late-model solid-axle Chevy that was experiencing front driveshaft bind at the axle. Installation is no different than that of a standard U-joint except that it is possible to install the joint backwards, which is another new twist of the Super-Flex.
Wacky-looking, simple and effective-all words that describe the new Super-Flex U-joint. Its unique design of offset trunnions sets the mating yokes farther apart than a conventional joint. Wood says that this allows for 10 degrees more flexibility than would be obtainable with a conventional joint. He notes that 10 degrees may not sound like a lot, but with a 30-inch driveshaft, this will allow more than 5 inches of additional droop at the axle prior to binding of the universal joint. His testing has shown that when this U-joint is installed in standard yokes, the driveshaft will flex to 40 degrees. With grinding, the driveshaft will flex to 45 degrees. The Super-Flex joint is available in 1310 and 1350 series. | 
Before: After a solid-axle conversion and a 9-inch suspension lift, our late-model Chevy's driveshaft yoke was binding against the pinion yoke at full droop. Since the front driveshaft wouldn't even turn, we ground the pinion shaft to eliminate the bind. Sure, we could have reindexed the front axle, but remember that substantial reindexing adversely affects the ability to align your vehicle, namely in regard to the caster adjustment. If you're having a front axle custom built, you probably won't need the Super-Flex U-joint because your builder will factor in the amount of lift your vehicle has and install the axle "Cs" in relation to how much reindexing is required. This will help your front axle retain its alignment adjustability. | 
After: With the Super-Flex U-joint installed, the two yokes are significantly farther apart at full droop. Because the Super-Flex has offset trunnions, there can be driveshaft vibration. Generally, the amount of vibration varies by vehicle and is relative to the angle of the driveline and the rpm of the shaft. Naturally, you wouldn't want to install a Super-Flex on the front driveshaft of a vehicle that doesn't have lockout hubs due to the vibration. With the four-wheel-drive system engaged, our Chevy exhibited medium driveline vibration up through 30 mph and light driveline vibration through 45 mph. Bottom line: The Super-Flex is designed to solve binding issues, but it's important to recognize its inherent limitations and abide by the manufacturer's recommendations. |