Synergy Suspension Jeep Heavy Duty Ball Joint sets are designed to replace the factory ball joint that is prone to premature failure on lifted Jeep’s with large off-road tires, although we see the OE ball joints fail on stock Jeeps all the time. See the next photo. Synergy ball joints are a fully greasable, sintered-metal-on-bushing design that has high wear resistance. The ball joint boot is made from strong polyurethane that’s tear and wear resistant. The complete set includes two upper and two lower ball joints that have a 12-month unlimited warranty.