THM 4L60-E – New Design 1-2 Accumulator Piston

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 .

New Design 1-2 Accumulator Piston


A 1984 through 1987 vehicle equipped with a THM 440-T4 transaxle may have an intermittent no reverse or locking in reverse condition un-til shifted to a forward range prior to shifting into reverse (“un-loading” the parking pawl). This condition may be caused by a “dent” on the parking paw1 that does not allow the paw1 to release until “un-loaded”. You can get more obd code scanners for help.

Date of Production Change: (Figure 1)
Effective May 1, 1987 (Julian Date 121) all 1987 THM 440-T4 transaxles were produced with parking paw1 assemblies not having a “dent”.

Service Action: (Figures 2 and 3)
If this condition is encountered, remove transaxle and replace the final drive internal gear/parking paw1 assembly (No. 673) and actuator guide, plunger and spring assembly (No. 709 – No. 711). Also inspect the parking gear for wear or damage and replace if necessary.

Service Parts Information:
Part Number                       Description
8656372                          Final Drive Internal Gear/Parking Paw1 Assembly
8656689                          Actuator Guide, Plunger and Spring Assembly
8644238                          Parking Gear

Service Notes: (Figure 2)
Before installing the replacement parts , inspect the new final drive internal gear/parking paw1 assembly to make sure it does not have a “dent”.  Some hot car tools like Launch CR-HD and SKT100 may bring you more information.