Yeah, but they probably call it COMPOSITE so they can charge more.

 

Charge more? Dunno. Here's what GM published in their "update" manual for 4L60Es:


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Technical Service Information


THM 4L60-E
ACCUMULATOR PISTON WEAR


COMPLAINT: When the accumulator piston wears with an "Egg-Shaped" hole where the accumulator piston strokes, it can create a delayed engagement to drive, slipping condition in forward gears, slipping 1-2 shift, slipping 3-4 shift, depending on which accumulator piston is worn, and how bad it is worn.

CAUSE: The cause may be, a worn accumulator piston pin bore (See Figure 1).

CORRECTION: Replace the accumulator piston with the proper part number from "Service Information" as
shown below.

SERVICE INFORMATION:

1-2 Accumulator Piston (Package of 2) .................................................. ............. 8684429
3-4 Accumulator Piston (Package of 2) .................................................. ............. 8682096
Forward Clutch Accumulator Piston .................................................. ................. 8679738


Service Note:

The THM 4L60-E, 3-4 accumulator piston is same as 700-R4.
The THM 4L60-E, 1-2 accumulator piston has a smaller pin diameter.
The THM 4L60-E, forward accumulator piston is a smaller outside diameter.


AUTOMATIC TRANSMISSION SERVICE GROUP
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Now... here's a bit more info on the following page...

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Technical Service Information

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.

REASON: More cost effective than the aluminum piston.

PARTS AFFECTED:

(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.
INTERCHANGEABILITY:

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.

SERVICE INFORMATION:

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.

AUTOMATIC TRANSMISSION SERVICE GROUP
-------------------------------------------------

Now... IMO, it seems as though GM said fix the expanding bore issue, but make sure you do so cost effectively. So, some genius decides to replace the aluminum design with a plastic design that has now been proven to potentially be worse due to cracking. In which cracking/breaking could result in trash being in the trans case "potentially" causing blockage. Is this a better alternative? Has the aluminum piston design gotten better? Dunno. This is where the gurus step in a provide product insight/knowledge based on experience.

FLT & Performabuilt (and any others)... there's your cue!