How to Rebuild a 604 Transmission


An automobile's transmission is responsible for converting an engine's power into torque with the aid of gears and clutches. As one type of transmission, the A604 is known for releasing and applying one gear at a time without using bands or sprags. With a fairly high amount of automobile knowledge and a few spare days, you can rebuild an ailing A604 transmission and restore it to an effective, working condition.

Things You'll Need

  • Transmission jack
  • Oil pan
  • A604 transmission overhaul/rebuild kit
  • A604 transmission manual
  • Differential safety pins
  • Impact wrenches
  • Blow gun
  • Sockets
  • Wrenches
  • Pliers
  • Drive gears


  • Remove the existing A604 transmission and place it on the transmission jack. Use the impact wrench to loosen all of the screws and bolts that are holding the transmission in place.

  • Let all of the transmission fluid drain into an oil pan. As the transmission fluid is draining, remove the transfer plate and valve-body assembly pieces. Use the blow gun to spray off the transfer plate and valve body to remove any debris.

  • Set those off to the side. The other parts of the transmission including the gears, pump assembly, input drum and sun gear shell will be replaced with the A604 rebuild kit.

Rebuilding the A604

  • Install the underdrive clutch pack into the steel clutch separating plates. Use a wrench to screw the snap ring into the clutch balancer. These components will twist into the underdrive clutch piston. Slide the clutch piston into the underdrive clutch drum oring, so it fits inside the underdrive clutch drum. Once the clutch pack is in place, install the underdrive, overdrive reaction plate, overdrive pressure plate and snap-ring.

  • Install the thrust washer and overdrive shaft. Use a wrench to tighten the nuts and washers to the rear flange of the adapter plate. Once these components are in, you can install the rebuild kit's pre-adjusted clutch pack into the input drum.

  • Install the reverse clutch in the input drum. Secure the bolts that hold the pump to the transmission with an impact wrench. After this, test the clearance of this component to ensure the transmission will fit inside the vehicle upon completion. Place the completed input drum inside the inside transmission.

  • Apply a small amount of automobile lubricant on the inside of the pinion-shaft bearing cup. Place the pinion-shaft bearing cup on top of the input drum. Screw it into onto the input drum with a wrench.

  • Install the rear planet by moving the gears to make sure there is enough clearance within the transmission. Use a wrench to then secure the three washers that will hold the rear planet in place. Install the output shaft to opposing side of the transmission by sliding a new seal between the shaft and the transmission. Work on the front sun gears and the four accumulators by adding new seal rings to these pieces and install these into a 2-4 clutch pack by securing the appropriate bolts.

  • Take the 2-4 clutch pack and install it into the rebuild kit's oil pump by using an impact wrench to tightly fasten the bolts. Once the oil pump's cover is sealed on, the pump cannot move or it will be damaged.

  • Install the oil pump and rebuild kit's bearings with the designated wrenches and bolts listed in the rebuild kit's manual.

  • Place the transmission back in the automobile and reattach the value body and transfer plates.

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