Single-sided Z-PAK friction set for the GM 4L60E 3-4 clutch that raises torque capacity and drops pack temperature without adding stack height.
Rebuilding a 4L60E that keeps burning its 3-4 clutch in a tow rig, a work truck, a lifted 4x4 or a fleet van? The Raybestos Powertrain RZP-001 Z-PAK is the heavy duty answer for that one clutch. Instead of cramming more double-sided frictions and steels into the drum, it uses single-sided plates, each carrying GPZ friction material on one face and acting as the reaction surface on the other. The result is more working friction surface in the same 3-4 space, and a pack that runs cooler under the loads that kill the stock clutch.
The 3-4 clutch applies on the 2-3 upshift and holds through fourth, so a truck cruising in overdrive is loading it the whole time. In a conventional pack, a lined friction sits between two plain steels, and heat from the linings has to cross into those steels. Raybestos builds the Z-PAK as interleaved single-sided plates: seven with outside-diameter splines and seven with inside-diameter splines, plus a 3-4 GPZ plate, the apply plate, a press plate and an optional OD spline shim. Raybestos states the module significantly reduces maximum core temperature, eliminates coning under high stress, raises torque capacity and outperforms both single and double sided OE clutches. It also says its GPZ material tests up to 20 percent better than OE friction. The pack is made in the USA.
Stripped reaction sun shell splines can also leave a 4L60E with no third or fourth, and a sun shell failure will not be fixed by any clutch pack. Confirm on teardown.
A burnt 3-4 pack is almost always the result of something else. Sonnax puts most 3-4 slipping down to low line pressure or third gear oil leaking somewhere along a long circuit tied into the D4, forward clutch, second clutch and third accumulator passages. Before you pay for a premium pack, air check the loaded drum, inspect the 3-4 piston for cracks, check the input housing check ball and the input shaft sealing rings, and vacuum test the pump boost and pressure regulator valves. The 3-4 clutch failure diagnosis guide covers the full sequence, and our friction count and upgrade comparison puts the Z-PAK next to the higher-count double-sided options.
RZP-001 is the 3-4 Z-PAK module for the GM 4L60E. The 4L60E went into Silverado, Sierra, Tahoe, Yukon, Suburban, S10, Blazer, Camaro and Corvette applications over a long production run, and input housings changed along the way. Because the Z-PAK plate count and thickness are different from the factory stack, measure your stack height and clearance on assembly rather than assuming it drops in. If you want a fitment check first, send us the year and VIN. Browse the rest of the unit on the 4L60E parts page.
Bed the pack in with light throttle for the first few hundred miles before putting a trailer behind it.
| Part number | Raybestos Powertrain RZP-001 |
| Fitment | GM 4L60E automatic transmission, 3-4 clutch |
| Plate design | Single-sided Z-PAK (friction bonded to the reaction plate) |
| Benefit | Higher torque capacity and lower pack temperature at the same pack thickness |
| Construction | Built to resist coning under high stress |
| Applications | Rebuild, commercial, fleet, four-wheel drive and heavy duty |
Doing this repair right usually means replacing these at the same time. Same transmission, ships together.
Per Raybestos: one 3-4 GPZ plate, one 3-4 apply plate, one 3-4 press plate, seven single-sided OD spline GPZ plates, seven single-sided ID spline GPZ plates and one optional OD spline shim.
Each plate has friction on one face and serves as the reaction surface on the other, so there are no separate plain steels. That puts more friction surface in the same drum space and helps pull heat out of the pack.
Do not assume so. The plate count and thickness differ from the factory pack, so measure stack height and set clearance on assembly, using the optional shim if needed.
No. Raybestos positions it for every rebuild including heavy duty, and it suits tow vehicles, 4x4s and fleet trucks that load the 3-4 clutch in overdrive.
Dexron VI ATF in a 4L60E. Soak the plates in it for at least 30 minutes before assembly.
New load release springs, the 3-4 piston if cracked, the input shaft sealing rings and anything that drops line pressure, such as a worn pump or pressure regulator valve.
