Clutch plates are used to create a connection between two metal parts, be it the input drum clutch disc’s of a 4L60E transmission or the clutch that pairs your flywheel to your transmission. When the friction material on the clutch disc comes into contact with both metal surfaces, it temporarily bonds them together through friction. The ideal clutch will have zero slippage; when it is applied, it will grab onto both surfaces and hold them in sync until it is released. The biggest problem with grease or other fluids on a clutch disc is that as heat builds from friction the grease will be pulled to the top of the material and in turn create slippage; sometimes to the point the clutch is unusable and must be replaced.
First and foremost you need to inspect and determine how bad the grease has actually contaminated the disc. If the grease was rubbed in or forced into the friction material by pressure from wiping, it is likely ruined dependant on the area and will not be worth the risk of the labor involved if cleaning is unsuccessful. If the grease contamination is lighter, and hasn’t been forced into the material, there are a couple old “tricks” that will help revive the clutch disc to save you from having to purchase a replacement.
Brake cleaner is non-lubricating, quick drying, and dissolves grease or oil in a hot second. On smaller areas where a glob of grease may have been applied you can spray the friction material down with brake cleaner. As you work the grease off the disc, maintain one direction of spray and try to get the fluid under the grease. For larger areas of contamination you can also soak the clutch disc in brake cleaner for around 12 hours or so, give it a quick spray down of brake cleaner and allow it to dry. Don’t be so sure the clutch disc has been saved; inspect it carefully, the last thing you want to do is repeat the labor involved to replace a clutch.
Essentially as the clutch creates friction between the flywheel and pressure plate, it will heat up and wick or pull any oil or grease from within the material and coat the pressure plate and the rest of the clutch disc. When the grease is released onto the pressure plate it will lubricate the surface and cause the clutch to slip; in some cases you will not even be able to drive but even when you can it will be like driving with a worn clutch. You can turn on your kitchen oven and place the clutch disc in the oven and allow it to bake until fluid is no longer wicking from the material. Pay attention to the boiling point of the grease it is contaminated with, because will have to exceed that temperature. Also keep an eye on the disc as it bakes; fires can start in the most random times and you don’t want to worry about replacing your over or even worse, your house.
Aside from the methods listed above the only other way to get grease off of a clutch disc is to lightly use a torch until all the grease is removed. Keep in mind if your clutch material is bonded instead of riveted, extreme heat could cause the bonding to fail. Before you opt to attempt a cleaning that may or may not work, you need to evaluate how much time you have along with the ambition to repeat the clutch replacement job again in the near future. If you can get the grease removed more power to you, but be for warned sometimes the better option is to spring the extra 200 bucks for a new clutch just to be safe. Remember even the slightest contamination can cause problems and slippage from your clutch disc.