CHANGE: Beginning on May 11, 1998 (Julian Date 131) all THM 4L60-E transmissions were built with a new design plastic 1-2 Accumulator Piston, and an ovate (oval) wire outer accumulator spring, to replace the previous design aluminum piston and round wire outer accumulator spring, as shown in Figure 1. Like to find obd code scanners for help?
REASON: More cost effective than the aluminum piston.
(1)1-2 ACCUMULATOR PISTON – Now manufactured out of plastic instead of the previous aluminum, which necessitated a dimensional change, as the plastic piston is thicker as shown in Figure 1.
(2)1-2 ACCUMULATOR OUTER SPRING – Now manufactured out of an ovate (oval) wire instead of the previous design round wire, to eliminate coil bind as shown in Figure 1.
The different 1-2 Accumulator Pistons and Outer Springs are not interchangeable. When replacing these parts you must remove the 1-2 Accumulator Assembly and inspect for the presence of either the aluminum or plastic 1-2 accumulator piston.
The plastic piston must use the ovate wire outer spring, and the aluminum piston must use the round wire outer spring to ensure against coil bind and spring breakage.
Refer to “Service Information” below for the proper service package part numbers if replacement is necessary.
1-2 Accum. Piston Service Package, 4L60, (1982-1993 Aluminum) …………………….. 24204495
1-2 Accum. Piston Service Package, 4L60-E, (1994-1997 Aluminum)………………….. 24204496
1-2 Accum. Piston Service Package, 4L60-E, (1998-1999 Plastic) ……………………….. 24214343
Note: All service packages include the proper outer spring. Here recommend the car tool Launch Cresetter .