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. To repair and prevent this problem, plus more easily tune 4C performance, Sonnax offers 4C retaining ring and shim kit 72978-01K with three essential parts for a reliable build.

The custom G-Loc ring in the Sonnax kit mechanically holds the OE retaining ring in place to prevent it from popping out.

The kit’s .078" thick clutch backing plate retaining ring makes it easier to achieve the 4C clearance specification of .030 to .055". Setting this clearance is difficult when OE selective backing plate retaining rings are not readily available. As a result, some builders use thinner steel plates, but this undermines the clutch pack’s ability to dissipate heat. The ring in the Sonnax kit is .010 " thinner than the ring most units have from the factory, allowing for more choices when setting clutch clearance.

The spring pack shim in the kit gives the option slightly tune the 4C clutch to release more quickly. Combining the shim with the thinner backing plate retaining ring and setting clearance closer to the high end of spec will preload the return spring for increased force. The result is improved 4C to OD shift timing when more aggressive, quicker-applying OD clutch packs are used.

• Prevents 4C return spring retaining ring from popping off
• More options when setting clutch clearance
• Improves 4C to OD shift timing