You are bleeding the trapped air in the casting passages and between the piston lands. This needs to be done, FIRST. But you don't have to do it on a "bench"; you can just leave it as-is on the firewall or vacuum booster. You merely back-off the flare nuts on the M/C, pull those lines back just a bit, and put the little M/C bleeder hoses into the exit holes in the fittings and run the hoses up into each reservoir. Just use your foot on the brake pedal to SLOWLY cycle the brake pedal until you see NO BUBBLES in the reservoir fluid. You need to be careful doing this so that: (1) you don't cause the bleeder lines to flop out of the reservoirs with too much pedal speed, and (2) you see the very fine bubbles near the end of this process.

Once the bubbles have stopped, pull the bleeder hoses out (put a cloth under the exit holes to catch any drips--it will not just flow out), reconnect the brake lines, top off the reservoirs (if needed), snap the cap back on the M/C and start bleeding the brake lines/calipers.

P.S. Tapping the calipers (FIRMLY with a rubber mallet) as the pressure bleeder is forcing fluid through the system is a VERY GOOD idea. The fluid cavities in the calipters have a bit of area that actually is higher than the bleeder outlet....so it's tough to get air out of there. I always drive the car over some rough roads/ R.R. tracks after bleeding the brakes. THEN I bleed them one last time, just to purge those bits of trapped air, finally dislodged out of the fluid cavities by bounding the car around. The pressure bleeder and rubber mallet method makes this portion of the process much easier.

Also, you must have a bottle (preferably clear glass) with some brake fluid already in it and the bleeder hose end submerged in that fluid, when bleeding each caliper using the 'brake pedal' method. When you slowly release the brake pedal, fluid will be drawn back into the bleeder hose. With the end submerged, NO AIR will get sucked back in.

 

That isn't quite correct. Yes, you will get some air drawn through the threads of the loosened bleeder screw, but keep in mind, that the air that's drawn in, is drawn in BEYOND the fluid cavities in the caliper. Since you've established a vacuum at the head of the bleeder screw, there's no "backflow" into the body of the caliper. HOWEVER, by this air being drawn through the threads of the bleeder screw, you will see a constant stream of air bubbles in the hose that you've attached to the vacuum tool, which WILL make it difficult to determine when the brake fluid has fully filled the line, and is being drawn into the bleed tool, and the bubbles you see, are just from the bleeder screw leakage.

HOWEVER.....if you're using the somewhat popular "speed bleeders", then YES, the threads of the speed bleeders have to seal to the body of the caliper, 100%. This is because when you push down the brake pedal, with the bleed screw in the "open" position, you create positive pressure, and push fluid/trapped air from the brake line. But as you release the brake pedal, you create a vacuum in the line, and unless the bleeder's threads have a 100% vacuum tight seal, this WILL draw air back into the caliper.

 

I own the rights to DOT 3 brake fluid. That's how I felt until I tried gravity bleeding. I always kind of looked down my nose at this technique. I have tried the Motive bleeder numerous times. I simply believe that somehow it was not getting all of the air out. My pedal never got hard enough for me using the Motive bleeder. So I decided to try the gravity bleeding method. It took some time to get all of the air out. Two hours roughly. It's now the best pedal and braking power that this car has had.
Not slamming the Motive at all. I'll use it again just not on my C3.
Craig

 

When you purchase your Dot 3 at your favorite store, note that all the plastic bottles of different brands have the similar number of ounces. What C3 owners need is stored out back. A 55 gal drum.

 

I remember, a few decades back, that Castrol used to have their brake fluid available in 1 gallon jugs......

 

leadfoot....
You are correct that air coming around the bleeder threads isn't really "air in the system". But, how do you KNOW that the bubbles in the bleeder line & dump jar are coming ONLY from the bleeder threads? That's right....you don't. So you just keep on bleeding and seeing bubbles in the line.

Your logic is just fine. But, you need a reality check on how to resolve the bubbles that are actually in the line....not just in your mind when thinking about it.

Thanks for your input...

 

I understand your point, and YES, there is a bit of doubt, with respect to the origin of the air bubbles. But generally, and I use that term carefully, after you pull 6-8 oz. of fluid from the system, the odds are pretty good that you've pulled all the air from the lines/calipers.

 

Bottom line--- If you see air bubbles, you keep bleeding....

 

I've had decent results with heavy grease, or even play doh around the bleeders in the past.

The last time I was bleeding brakes, I just picked up 25 feet of clear plastic hose, and ran it all the way from each bleeder up to the master cylinder reservoir. Pumped the brakes and watched the fluid flowing through the tubing till it was clear. No risk of running the reservoir dry

 

That will work....as long as you want to KEEP that old fluid in your brake system. Most of the time, you want to replace it with fresh fluid, anyway. But, that method is an option, if the fluid is clean.

 

I just used the Motive bleeder over the weekend and worked great. I bought it with all the adapters to handle all my cars.