A shudder type of a feeling may be felt during a first to second shift transition. When the transmission is disassembled, the Direct Clutches may show signs of discoloration with the friction plates.
The cause may be that the upper sealing ring groove on the Direct Clutch drum support has developed excessive clearance. This allows Direct Clutch apply pressure to leak past the ring and intrude into the lube circuit. This increases the pressure between the counter balance piston and the face side of the Direct Clutch piston. This does two things; the apply pressure behind the large diameter piston has decreased due to the leak while increasing lube pressure opposing the application of the piston. This compromises the apply rate of the clutch causing the shudder sensation.
The Direct Clutch is applied in second by way of two pistons; a large and a small. The clutch assembly is then held on by both of these pistons for second and third gears. In fourth gear, the apply pressure behind the large piston is exhausted, thus relying on the smaller piston to keep the assembly applied. The apply pressure behind the smaller piston is then exhausted during a four to five shift fully releasing the clutch assembly.
This is double piston apply strategy is a very unique way to control the apply and release of a clutch. The first to second shift transition requires a great deal more piston surface area to complete the shift successfully. Not only is the ratio change significant during this transition, it is also under a greater load when compared to a five to four shift. Once applied, the pressure behind a double piston strategy offers greater holding capacity throughout second and third gears. Only a smaller piston area is then needed to hold the clutch on while in fourth gear. This small clutch apply also offers a smoother five to four shift transition. This would explain why only the shudder is noticed on the one to two shift transition and not the five to four shift.
To correct this condition, inspect the sealing ring to ring land clearance after a new set of rings have been installed. If the clearance exceeds .005” replace the drum support. Note: Measure all three rings in their ring lands and compare the readings, as they should be the same. Ensure the piston seals are new and the Direct Drum is assembled correctly.
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