How to Rebuild a 4R100 Transmission


The 4R100 transmission is a sturdy and heavy-duty transmission preferred by off-road enthusiasts due to its ease of maintenance and seemingly infinite upgrade possibilities. If you have come into possession of a 4R100 transmission that is in need of a rebuild before it starts its off-road duties, it may seem a daunting task. However, rebuilding a 4R100 transmission is not as difficult as it may seem and can be undertaken by any ambitious home mechanic.

Things You'll Need

  • Socket wrench set
  • Jack stands
  • Allen wrenches
  • Transmission rebuild kit
  • Small hand-held grinder
  • Unbolt all of the mounting bolts on the outside edges of the transmission and pull the bell housing apart with the pinion rods, which are the small cylindrical metal rods grouped in sets of three and mounted to the inside wall.

  • Find the rear pinion gears (the gears or cogs located on the lower rear portion of each of the three control arms: lower, upper and gear shift) and slide the new rear gear from the rebuild kit into the slot on each. Use the Allen wrenches to tighten down the set screws, which are the tiny screws located in the middle of each pinion gear, to hold them in place.

  • Pull the two long metal shafts extending through the transmission (also known as spindle shafts) out to inspect them and use a grinder to hone any nicks or scratches out of the shaft and replace the housing bushings (the round rubber pushing in place between the spindle shaft and the housing mating surfaces).

  • Place the gasket between the two portions of the bell housing, mate the two pieces back together and install the mounting bolts.

Tips & Warnings

  • If the transmission is mounted in a vehicle, use a car jack to lower it out of the vehicle before beginning any work on it and make sure a helper assists in removing it from the undercarriage as this can be a dangerous job.

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