How To Replace The Transmission Tail Shaft Seal On A 1986 GMC Jimmy

You know you are leaking transmission fluid when you see little puddles of pink on your driveway where your vehicle was parked. There are several areas where the leak could be coming from including the tail shaft seal. The tail shaft is the back part of your transmission and you'll need to replace the seal and bearing to stop the leak. This is a project many amateur mechanics can do by themselves. If you find you have a leak at your tail shaft seal, here is how you can replace the seal and bearing on the tail shaft of a 1986 GMC Jimmy (this procedure is virtually the same for other rear wheel drive vehicles – although the size of the wrenches might be different).

You Will Need:

  • New Gasket
  • 7/16" Wrench
  • Rubber Mallet
  • Large Hammer
  • Flat Head Screwdriver
  • Torque Wrench

Tail Shaft Seal Location

Slide under the Jimmy and look at the back end of the transmission. The seal and bearing you have to replace are located where the drive shaft enters into the tail end of the transmission.

Remove Drive Shaft

Put the truck in gear to keep the drive shaft from spinning around. You need to remove the four 7/16" bolts for the u-shaped brackets that hold the back end of the drive shaft to the back axle. Use a flathead screwdriver to scratch the yoke on the drive shaft and the axle so you can line up the scratches when putting the drive shaft back together. This ensures you put it back together correctly since the yoke will spin around. Use a large flat head screwdriver to pry the drive shaft out of the bracket on the axle.

Place a catch basin underneath the spot where the front of the drive shaft and the tail shaft meet. Pull the drive shaft out. The catch basin will capture any transmission fluid that leaks out.

Remove Seal and Bearing

You need to remove the seal and bearing at the very end of the tail shaft. Use a large hammer and the flathead screwdriver to force the edge of the bearing out of the tail shaft. Once you get the bearing loose, you should be able to pry it with the screwdriver. Clean the area with a rag or paper towels.

Install New Seal and bearing

Place the new seal and bearing into the end of the tail shaft. Tap it in place with a rubber mallet. Make sure the bearing is placed evenly into the tail shaft. Slide the front end of the drive shaft into the tail shaft of the transmission and connect the back end of it to the axle. Make sure you line up the scratches on the yoke and axle before you bolt the brackets back on.