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The u-joint plays a critical role in the drivetrain. They are one of those parts that are simple in their task and therefore often taken for granted. Whether in the front axle or on a driveshaft, the u-joint’s capabilities need to be understood.
Doing The Job
U-joints or universal joints join spinning components together while allowing them to move up and down in coordination with the vehicle’s suspension. The cross-shaped units join driveshafts to transmissions/transfer cases, differentials, and other sections of driveshafts. They also connect two-piece front axles.
Types Of U-Joints
There are two types of u-joints; sealed greaseable and non-greaseable. There is a long-standing debate over which style of u-joint is stronger. But independent lab testing done by various entities have proven neither style has a clear, real world advantage. You will see a four-digit number accompanying many u-joint descriptions. The numbers, 1310, 1350, 1410, 1550, and others, refer to the series, or size, of the u-joint which is determined by its dimensions.
Lubrication Importance.jpg)
Putting all the specs aside, lubrication shortcomings are the most common cause of u-joint failure. Not keeping up with general maintenance in a greaseable unit or contamination of the lubricant in a sealed, non-greaseable joint. Other culprits include plain old wear and improper installation or poor build quality, i.e. the use of poor-quality grease or using too little grease, in a non-greaseable u-joint.
Torque Multiplication
When talking about strength and durability of front axle u-joints one must remember there is a torque multiplication factor at work here. It comes into play when the front driveline experiences angles and at a maximum angle of 40 degrees 30% more torque can be projected onto the u-joint. The multiplication is nominal up to 15 degrees and then the curve progresses from there. This means that a u-joint that is working near its yield point can deform if you’re crawling or bogging and putting a max load on the driveline via angularity. The workaround is to keep your wheels as straight as possible during these high load situations.
Ring Clips FTW
If a u-joint is being pushed to failure there are ways to increase its survivability envelope or at the very least prolong its life momentarily. It’s all about rings and clips. Using full circle snap rings in place of the traditional c-clips will resist distortion of the joint as the yoke ears begin to thrust the caps out of place. The c-clips usually used to secure the caps cannot resist the side forces very well but the full circle clips will do a better job and therefore help delay u-joint failure. The full circle clips must be installed at assembly and OE axles may require some clearancing in the yoke to allow fitment. Many aftermarket axles have grooving large enough to accommodate full circle clips.
Weak Links
There are two primary failure points in conventional OE-spec u-joints – the cross and the caps. The failure scenario plays out at the caps. Typically, in OE-style axles the yokes will be stressed to distortion and as they spread outward the caps are also affected. The caps move and eventually destroy the needle bearings and often become dislodged from the yoke and fall off. If the caps somehow survive the cross itself can suffer the effects of the stress by distorting and failing.
Yukon Super Joints
Yukon Super Joints offer an upgrade in strength and durability over factory u-joints and excel in off-road applications. Designed for Dana 60, Dana 44, Dana 30, and GM 8.5” differentials, Yukon Super Joints feature a 4340 chromoly cross and the caps are made from 4140 steel. The caps are formed from slightly softer steel to isolate the wear to the caps not the cross because it’s a lot more convenient and less expensive to replace the caps. A diamond-like coating offers outstanding wear resistance on the trunnions and corrosive resistance for the entire cross. The end of each trunnion is home to a reservoir for the grease. You’ll notice the trunnion is larger in circumference compared to conventional u-joints. This is the result of eliminating the needle bearings entirely, replacing them with a bushing setup. These joints were never designed for daily drivers. They require fanatical maintenance, greasing each of the eight caps after each long trail run. We do not recommend installing them in a vehicle that does not have locking hubs… this is NOT one of those products you can ‘get by’ with on the street. If they lose their lubrication properties the joints can gall and lock up the vehicle’s steering. They are intended for competition vehicles or dedicated off-roaders that strictly run the trails.
Along with the Super Joint(s) and caps you’ll receive an installation manual, sticker, grease gun, high-quality anti-seize grease, and associated small parts like O-rings, zerk fittings, and a set of full-circle snap ring clips.
Yokes and u-joints are critical links in the drivetrain’s chain of performance. Ensuring your yokes and u-joints are strong enough and properly maintained will keep you and your ride running smoothly for years to come.
