March 11, 2021
Accumulator piston scuffing and bore wear are common issues in many Chrysler valve bodies, especially when running increased pressures. Although various fixes have been tried over the years, from changing the seals to improving piston material, testing proves they range from completely ineffective to actually creating new problems. Let’s take a close look at seal function so you understand what’s at stake and the unique benefits Sonnax heavy duty accumulator pistons bring to your builds.
A unique combination of features allows Sonnax billet aluminum accumulator pistons to safely and reliably address every piston problem. There’s no risk of transmission failure from broken, late-model plastic parts thanks to the piston’s much stronger material. The relocated, scarf-cut primary seal allows moderately worn bores to be salvaged. And, unlike any other aftermarket piston, durability is further improved by stabilizing the piston with two guide seals to prevent piston-to-bore scuffing. Since these unique pistons from Sonnax are a relatively recent repair option, it’s both interesting and educational to understand how we got here.
|Single Piston Kit||5-Piece Piston Kit|
|Part No. 44894-01K||Part No. 44894-01MK|
The accumulator piston in the popular 68RFE transmission is the same basic piston used in other electronically controlled Chrysler units, including the 62TE and the older 41TE/604 models. Over the years as shops have struggled with clutch durability issues, there have been attempts to change the accumulator seals from the original, scarf-cut, PTFE-type seals to rubber O-rings or rubber quad-rings.
When you evaluate the effectiveness of rubber, though, it proves not to be the best solution for the RFE units. Interestingly, when the scarf-cut seal and OE accumulator are hydraulically leak-checked, they actually seal excellently and are not a significant source of leakage. Unlike many other common accumulators, these RFE accumulators do not have oil pressure on the back side of the piston and rely only on springs for resistance to movement and accumulator action. With less overall resistance, the “compression” of the rubber seals can create enough friction and drag of the piston to adversely affect shifts in these sensitive RFE units.
A close look at the OE piston reveals the primary seal has a deeper (smaller diameter) groove that allows oil underneath the seal (Figure 1). There is also a vent slot/hole between the seals so the primary seal only has pressure on one side. The guide seal is the same scarf-cut part, but the groove diameter is larger — this holds the seal up so it protrudes above the piston diameter and prevents piston-to-bore scuffing. The problem with this OE design is that the piston is only fully supported at one end. When the piston is side loaded, the primary seal can sink into its deeper groove and allow the piston to contact the bore. This results in scuffing and a breakdown of the whole system.
Of the ever-increasing number of choices for aftermarket aluminum accumulator pistons, ONLY Sonnax heavy duty pistons have guide seals at both ends to prevent scuffing (Figure 2). These unique pistons also maintain a deep groove primary seal that is properly vented on the non-pressure side and relocate the primary seal to an un-worn portion of the valve body bore, all the while keeping the low-friction benefits of the OE-style seals.
|Figure 1 – OE Accumulator Piston|
|Figure 2 – Sonnax Heavy Duty Accumulator Piston|
Dual Guide seals allow Sonnax heavy duty pistons to stay straight in the bore while also allowing proper pressure and venting to the relocated primary seal.
Keep these great features in mind when you’re considering the options for improving 68RFE accumulator piston performance — the most reliable parts are those that truly improve transmission durability without introducing new problems or concerns.
Sonnax accumulator cover plate kit 44892-01K is an upgrade over OE that prevents plate failure and allows salvage of RFE valve bodies with damaged plates. This patented kit features:
|Accumulator Cover Plate Kit||Thread Tap|
|Part No. 44892-01K||Part No. 44892-TL|
March 11, 2021
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