The 4C return spring retaining ring in Chrysler 45RFE, 545RFE, 65RFE, 66RFE and 68RFE transmissions is known to come unseated and pop off resulting in transmission failure. Sonnax 4C retaining ring and shim kit 72978-01K includes three crucial pieces for setting up the 4C clutch in Chrysler RFE series transmissions. This kit includes a custom G-Loc ring that mechanically holds the OE retaining ring in place and prevents it from popping out. Setting clutch clearance in the 4C pack is difficult because oe selective backing plate retaining rings are not readily available. As a result some builders use thinner steel plates but this reduces heat dissipation of the 4C clutch pack. The 4C clearance specification is .030 - .055”. This kit includes a .078”
thick clutch backing plate retaining ring that is .010” thinner than the ring most units have from the factory for more choices when setting clutch clearance. Using the thinner backing plate retaining ring and setting clearance closer to the high end of spec plus installing the included spring pack shim in this kit preloads the return spring for increased force. The increased return spring force helps slightly tune the 4C clutch to release more quickly, improving 4C to OD shift timing when more aggressive quicker applying OD clutch packs are used.