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I've mentioned this in a couple of different threads, so I thought I would give it it's own thread for easier future reference. As of November 2006, GM updated all hydraulic clutch bleeding procedures to this method.
Use a hand Vacuum pump (these can be picked up for cheap at most auto parts stores or Sears). http://www.sears.com/shc/s/p_10153_12605_00999499000P
If you've never used a hand vacuum pump, here's a little crash course- You'll take one hose from the pump to the overflow cup and another hose from the cup to whatever you're pulling the vacuum on. For this you'll need to put a cone-shaped attachment on the end of the hose. Also make sure the reservior is sealed up well. Generally it's a two-piece design with a screw-on lid. Put a small layer of grease around the top of the cup then put the lid on. It sounds crazy, but I've found that dielectric grease works great for this.
Make sure your reservior is filled with fluid (take the rubber insert out for this, if there is one there). Insert the end of the hose into the master cylinder reservior and push the cone down into the hole in the bottom of it and hold it there. Begin pumping the vacuum pump and you'll see fluid and air bubbles beginning to work their way up the hose and towards the overflow cup on the vacuum pump. Pump until you see about 15-18in.Hg vacuum (do not exceed 20in.Hg, as it could damage the master cylinder). Hold it there for a minute then quickly pull the end of the hose out of the master cylinder reservior. Make sure you pull it completely out of the fluid, because it will suck your reservior dry if you leave it in there. Now make sure there's plenty of fluid in the reservior then check your pedal. It'll most likely be on the floor. If not, usually one slight push on it will cause it to fall to the floor. By pulling it up you will suck the fluid in the reservior down into the master and slave cylinder, so make sure it's full before pulling the pedal up.
Repeat this process until you don't see any more bubbles coming up when you pull the vacuum on the system. You may have to empty the overflow cup several times.
This is also a good way to check for a leak in the system. If you continually see bubbles or have trouble maintaining a vacuum, then you have a leak somewhere. Also keep in mind that a leak in the master cylinder may not actually leak fluid out. In fact it most likely won't. A faulty master cylinder usually causes problems by leaking fluid past it's plunger, but not necessarily leaking out of the cylinder itself. Putting a vacuum on a faulty master cylinder will often cause air to leak IN. If this happens then you'll see a see a constant stream of bubbles and you'll never be able to hold a vacuum. A leak in the slave cylinder on the other hand will usually leak fluid OUT.
Hope this helps.
Use a hand Vacuum pump (these can be picked up for cheap at most auto parts stores or Sears). http://www.sears.com/shc/s/p_10153_12605_00999499000P
If you've never used a hand vacuum pump, here's a little crash course- You'll take one hose from the pump to the overflow cup and another hose from the cup to whatever you're pulling the vacuum on. For this you'll need to put a cone-shaped attachment on the end of the hose. Also make sure the reservior is sealed up well. Generally it's a two-piece design with a screw-on lid. Put a small layer of grease around the top of the cup then put the lid on. It sounds crazy, but I've found that dielectric grease works great for this.
Make sure your reservior is filled with fluid (take the rubber insert out for this, if there is one there). Insert the end of the hose into the master cylinder reservior and push the cone down into the hole in the bottom of it and hold it there. Begin pumping the vacuum pump and you'll see fluid and air bubbles beginning to work their way up the hose and towards the overflow cup on the vacuum pump. Pump until you see about 15-18in.Hg vacuum (do not exceed 20in.Hg, as it could damage the master cylinder). Hold it there for a minute then quickly pull the end of the hose out of the master cylinder reservior. Make sure you pull it completely out of the fluid, because it will suck your reservior dry if you leave it in there. Now make sure there's plenty of fluid in the reservior then check your pedal. It'll most likely be on the floor. If not, usually one slight push on it will cause it to fall to the floor. By pulling it up you will suck the fluid in the reservior down into the master and slave cylinder, so make sure it's full before pulling the pedal up.
Repeat this process until you don't see any more bubbles coming up when you pull the vacuum on the system. You may have to empty the overflow cup several times.
This is also a good way to check for a leak in the system. If you continually see bubbles or have trouble maintaining a vacuum, then you have a leak somewhere. Also keep in mind that a leak in the master cylinder may not actually leak fluid out. In fact it most likely won't. A faulty master cylinder usually causes problems by leaking fluid past it's plunger, but not necessarily leaking out of the cylinder itself. Putting a vacuum on a faulty master cylinder will often cause air to leak IN. If this happens then you'll see a see a constant stream of bubbles and you'll never be able to hold a vacuum. A leak in the slave cylinder on the other hand will usually leak fluid OUT.
Hope this helps.
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