4L80E Clutch Module, new and ready to install. Fits the 4L80E. Ships fast from the USA.
Tearing down a 4L80E from a towing Silverado or Sierra 2500, a 3500 dually, an Express or Savana van or a Hummer H1 and finding blue, warped or heat-checked steel plates means the steels have to go along with the frictions. This is the Raybestos Kolene steel clutch pack, part number STMGM08K, cataloged for the GM 4L80E and 4L85E from 1991 on. It is a full set of steel plates for the unit, made for a rebuild that has to live behind a heavy load or a built engine.
Every clutch in the 4L80E is a stack of friction plates splined to one part and steel plates splined to another. When the piston squeezes the stack, the steels give the friction lining a flat, hard surface to grab. The steels also soak up and shed most of the heat made during each shift. A steel that has warped, glazed or turned blue no longer sits flat, so the pack slips even with brand-new frictions. This module covers the whole transmission: four fourth clutch steels, four intermediate, three overrun and ten for the forward and direct packs.
Kolene is a salt bath nitriding process. Raybestos says it raises wear and fatigue resistance by 200 to 500 percent over an untreated plate and improves heat resistance and lubricity, which is why it is used in heavy-duty and performance rebuilds rather than a standard steel.
The steels can only be judged with the transmission apart. Lay each plate on a surface plate or a piece of glass and check for rock, then look for discoloration and scoring. If one pack burnt, find out why before reassembly. Low line pressure, a worn valve body or a converter clutch problem will burn new plates just as fast. Our 4L80E common problems guide and the 4L80E 3-4 clutch failure guide cover the root causes.
Raybestos lists STMGM08K for every 4L80E and 4L85E from 1991 on, so it works for both the early and the later design. The 4L85E is the heavier-duty version found in some 2000s trucks and vans. Even with wide coverage, count and compare your old plates against the module at teardown, check spline style and thickness, and send us your year and VIN if you are unsure. All of our 4L80E parts are listed on the 4L80E collection page.
| Fits | 4L80E |
| Part type | Clutch Module |
| Condition | New |
| Brand | Raybestos |
| Ships | From the USA |
| Warranty | 1-year |
Doing this repair right usually means replacing these at the same time. Same transmission, ships together.
No. STMGM08K is a steel plate module only. Pair it with a friction module for your year range.
Yes. Raybestos catalogs STMGM08K for the 4L80E and 4L85E from 1991 on.
Kolene is a salt bath nitriding treatment. Raybestos states it improves wear and fatigue resistance 200 to 500 percent and adds heat resistance and lubricity.
Twenty-one: four fourth clutch, four intermediate, three overrun and ten for the forward and direct clutches.
Only if every plate is flat, free of heat marks and not glazed. Heavy-duty and towing rebuilds usually replace them.
