How to Rebuild a C4 Transmission


The C4 transmission was first introduced in the 1964 Ford 3-speed automatic. The C4 was used in Fords until the C5 was introduced in 1984. During a rebuild, all bands and clutches will need to be replaced as well as the torque converter. Other parts are inspected for wear and will either be replaced or cleaned. The valve body is the most difficult part to rebuild because it is the most intricate and most important part of the transmission.

Things You'll Need

  • Garage
  • Complete set of tools
  • Manual
  • C4 build kit
  • 1970 or later C4 transmission
  • Purchase a C4 build kit. The build kit will contain the torque converter and all new gaskets, bands and clutches that need replaced.

  • Purchase a 1970 or later C4 transmission to use for parts. The transmission should be between a 1970 and 1983 model. A hardened aftermarket .839-inch, 26-spline input shaft is recommended.

  • Disassemble the transmission and lay out all the parts on your workbench. Separate the piles of parts that need cleaned and parts that will be replaced. There may still be fluid in certain compartments so be sure that the transmission is sitting on cardboard or something to protect your work space.

  • Rebuild the forward clutch assembly by stacking clutches and steels from the build kit. There should be a .045- to .060-inch side clearance when the clutch assembly is complete. The higher clearance is better for a firmer shift.

  • Inspect the forward and reverse gear planets. Clean or replace these units with the parts from the spare C4 transmission or locate a replacement part. Inspect and clean or replace any other individual components that can be completed outside of the transmission such as the clutch drum, the parking paw and the performance sprang.

  • Reassemble the newly built parts. Be sure to use the new gaskets from the build kit to seal everything. Use lubricant on parts that will encounter friction and additional sealant where needed. Begin the assembly with the smaller parts such as the sun gear and the shell.

  • Consult your manual for proper torque specifications when torquing the housing. Test the second gear servo piston, band struts and the intermediate servo piston with compressed air to ensure that the parts are working. The final piece should be the bellhousing.

Tips & Warnings

  • Be sure to use the proper transmission fluid that can handle temperatures of 250 to 300 degrees.
  • Check for Ford casting numbers on the housing for compatibility.
  • Always check the governor piston and spring.

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