SAC = Self Adjusting Clutch. This is a wedge mechanism in the pressure plate that over time & clutch wear, will adjust itself to keep the engagement point of the clutch at the same point. More importantly, it keeps the holding force consistant, but that’s not what the driver really relates to most of the time.
The reason it needs to be set/checked prior to install; This mechanism can be jarred out of alignment, and can be incorrectly installed in a “worn” position. If that’s the case, it will have less room for travel to release the clutch, and you can end up with several odd symptoms. Hard to shift with clutch pedal all the way down, Clutch pedal won’t go all the way down to start the car, and grinding noises with the clutch all the way down, to name a few. This condition can also smoke your brand new clutch in 4,000-5,000 miles if not corrected.
The pressure plate can be jarred out of position with simple vibrations. A nice drop will do it too, so if you see the UPS guy drop it on his truck, kick it across the room once, or if it falls to the floor while it’s being installed, it’ll be out of adjustment. Also, the adjustment piece is rather fragile IMO, so don’t go prying on it too hard!
Here’s my RS4 pressure plate, as it came in the box. Notice the multiple slots around the middle of the surface, and there’s nothing there….
Next, I set it up on the press, careful to support it by the surface that bolts to the flywheel. If you support it by the friction surface, you’ll risk damage to the assembly. I also use a strut top bushing to depress the clutch, since it’s softer, happens to be the perfect size, and risks less for damage.
Carefully depress the clutch, while watching the inside of the clutch. The SAC disc has wedges on it, that align with the slots on the pressure plate. You’ll need to find the point inside, to pry on GENTLY with a small screwdriver. Once it’s depressed enough, this adjustment will be as easy as typing on a keyboard. Don’t depress it too much….
Once you’ve done it correctly, this is what it should look like. If you can’t see the difference, maybe compare this picture with the first one… 😉
(Original:http://www.audiworld.com/tech/eng86.shtml) – By Mathew Reid