How to Replace the U-Joint in a 1999 Yamaha ATV

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Many of the ATVs produced by Yamaha in 1999 were powered by a shaft-driven transmission. A universal joint is used to join the drive shaft to the ATV's transmission, allowing the shaft to move with the ATV's rear wheels and suspension. The U-joint is protected from dirt and debris by a rubber boot. Over time, the boot can tear or stretch, allowing dirt particles to enter and contaminate the U-joint. If left unprotected for too long, the U-joint can rust into a solid mass or separate, preventing the driver shaft from turning.

Things You'll Need

  • 10, 12, 14 17 and 22 mm sockets
  • Socket wrench
  • Jacks
  • Flat screwdriver
  • Parts cleaning spray
  • Lithium soap-based grease
  • Pull the rubber caps off of the rear axle, positioned in the center of the wheels' hubs. Loosen the rear wheels' lug nuts and the hubs' center nut, using a 17 mm and a 22 mm socket and a socket wrench, respectively.

  • Lift the rear end of the ATV off of the ground with an ATV jack. Unscrew the rear wheel's lug nuts with your 17 mm socket, then pull the wheels off of the rear axle. Unscrew the hubs' center nuts with your 22 mm socket, then slide the hubs off of the rear axle.

  • Unscrew the rear brake caliper's mounting bolts, positioned on the left side of the rear axle, using a 12 mm socket. Slide the caliper off of the rear brake disc and hang it from the ATV's frame, using a bungee cord.

  • Slide the rear brake disc off of the left side of the rear axle. Pull the rear axle out from the right side of the rear swingarm. Unbolt the trailer hitch bracket from the swingarm, if equipped, using a 10 mm socket.

  • Place a jack under the swingarm's final drive gear, to large assembly that the rear axle was housed in. Unscrew the final drive gear's mounting nuts with a 14 mm socket. Pull the final drive gear away from the swingarm and the drive shaft. Set the final drive gear aside.

  • Pull the drive shaft and the U-joint out from the swingarm. Loosen the hose clamps securing the drive shaft's boot to the motor and the swingarm, using a flat screwdriver. Pull the boot away from the ATV and inspect it for cracks or tears. If no damage is visible, reinstall it onto the motor and the ATV. If the boot is damaged in any way, replace the boot with a new one.

  • Pull the U-joint off of the end of the drive shaft. Clean the drive shaft with a parts cleaning spray, then coat the shaft's male and female ends with a lithium soap-based grease. Place a new U-joint over the male end of the drive shaft. Coat the motor-end of the U-joint with a lithium soap-based grease. Insert the U-joint and drive shaft into the swingarm and onto the motor.

  • Lift the final drive gear into place against the swingarm, using a jack. Slip the female end of the drive shaft onto the splined shaft on the back of the final drive gear. Screw the gear's mounting nuts into place with your 14 mm socket. Reattach the trailer hitch bracket to the rear swingarm, using a 10 mm socket.

  • Push the rear axle through the right side of the swingarm. Slide the rear brake disc onto the left side of the rear axle. Slip the rear brake caliper over the brake disc, then bolt it into place with a 12 mm socket.

  • Slip the rear wheel's hubs onto both ends of the rear axle. Screw the hubs' center nuts loosely into place with a 22 mm socket. Mount the rear wheels onto both hubs and loosely screw the wheels' lug nuts into place with a 17 mm socket. Remove the ATV from your jack. Tighten the rear hubs' center nuts completely, followed by the rear wheels' lug nuts.

Tips & Warnings

  • There may be some differences in this procedure between the different ATV models produced by Yamaha. Refer to a factory service manual for detailed instructions tailored to your specific Yamaha ATV, as well as a list of torque specifications or special tools.

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References

  • "The Professional Motorcycle Repair Program"; Professional Career Development Institute; 1995
  • "Yamaha YFM400FWL Service Manual"; Yamaha Motor Corp.; 1999
  • "Yamaha YFM600FWAL Service Manual"; Yamaha Motor Corp.; 1999
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