Bonded clutch piston set for GM 4L60E and 4L65E, 1997-up 16-bolt pan units. Replaces cut or hardened piston seals during an overhaul.
Building a 4L60E or 4L65E for a lifted Silverado, a towing Tahoe or an LS-swapped Camaro means every clutch circuit has to hold full apply pressure, and the original rubber piston seals are usually the weak point after years of heat. The Hi-Per Blue 74960K kit (also listed as A74960EHPK) replaces them with bonded pistons, where the sealing lip is molded to the piston itself. Nothing to roll, nothing to cut, and no chance of a lip seal going in backwards.
Clutch packs in this transmission are applied by fluid pressure pushing a piston against the plates. Clamping force depends entirely on how much of that pressure stays behind the piston. A loose lip seal in a groove can twist or nick on assembly, and an old one shrinks and hardens until it bleeds. Either way the pack clamps lighter than the valve body intends, so it slips under load and heats up. With a bonded piston the lip and the piston are one part, so the only things left to get right are a clean bore and careful installation. That is why builders use them on 4L65E and high-torque 4L60E rebuilds where a marginal seal would show up first. The 4L65E carries more torque than the 4L60E, which makes a leak-free apply even more important.
On the bench, air check each clutch circuit with regulated shop air. A sealing piston strokes with a solid thump and holds; air escaping around the piston means the seal is gone. Our bench air check procedure walks through each feed hole. Sonnax points out that most 3-4 burnups trace back to low line pressure or a leak somewhere in the third-gear circuit, so test the input housing checkball, the 3rd accumulator and the pump at the same time. New pistons will not save a unit with a leaking circuit elsewhere. The 4L60E common problems guide lists the other usual suspects.
This kit is listed for the GM 4L60E and 4L65E with the 16-bolt pan, 1997 and later. Listed applications include 1999-2013 Silverado and Sierra 1500, 1997-2010 Tahoe, 2000-2011 Yukon, 1997-2014 Express and Savana, 1997-2005 Corvette, 1997-2002 Camaro and Firebird, 2003-2012 Colorado and Canyon, Trailblazer, Envoy, Hummer H2 and H3. Count the pan bolts before ordering; earlier units with a different pan are not covered by this listing. If you are unsure what is in your vehicle, send us your year and VIN, or browse the full 4L60E parts page for other versions.
| Fits | GM 4L60E, 4L65E (1997-up, 16-bolt pan) |
| Part number | 74960K / A74960EHPK |
| Type | Bonded piston set, Hi-Per Blue |
| Weight | 4 lb |
Doing this repair right usually means replacing these at the same time. Same transmission, ships together.
It is the Hi-Per Blue bonded piston kit 74960K, also listed as A74960EHPK.
This kit is listed for 1997 and later 4L60E and 4L65E with the 16-bolt pan. Count your pan bolts and send us your year and VIN if you are unsure.
Yes. The listing covers both the 4L60E and 4L65E with the 16-bolt pan, including Hummer H2 and later full-size trucks.
The lip is molded onto the piston, so it cannot roll, twist or be installed backwards, and it eliminates the old hardened seals that bleed apply pressure.
Only if the pistons are the leak. Air check every circuit and also test the input housing checkball, 3rd accumulator and pump, because a leak anywhere in the third-gear circuit burns the pack.
