I have replaced the fluid in my C7 Grandsport a few times now, and I think I still have air in the line some where
The last time I changed it, when I took it out for a test drive the brakes were razor sharp, instant bite, the next day however the brakes felt like they had much less initial bite, they still seem to brake well over all, but nothing like when i first bought the car or that last test drive. I suspect there is air in the line somewhere and my fluid replacement process is not getting it all out.
I do think that i may be draining too much fluid from the rears and by the time i get to the fronts, i am running low on fluid, last time i did the fluid i went through 4 pints

 

Ok here are some suggestions, first check the master cylinder after bleeding each wheel refill as needed.
Second make sure the bleed screws are tight! Don’t make them too tight just a tug after they are seated.
Make sure the hose in the bleeder bottle is covered with a bit of fluid when you start.
If you are just starting get some one to press and release the brake pedal so you can close the bleeder before the up stroke.
Four or five strokes will usually do it.
If you get air in the ECBM pump drive it a bit and stand on the brakes to cycle the pump & valves Then bleed again until no bubbles come out into the bleeder bottle.
If all else fails you may need a power bleed (done at a dealer)

 

you do not want the tank to run dry.
So bleed one caliper then top off before moving to the next caliper. It takes me 3 pints and I use a Motive pressure bleeder.

 

This may be a stupid question but when I first start using the pump bottle to replace the fluid, the hose is empty until you pressurize the bottle and start releasing fluid, isn’t all that air making it’s way into the brake system? I use a motive pressure bleeder

 

The secret to using the Motive Pressure Bleeder is to not put fluid in the Pressure Bleeder Bottle. Just suck all of the brake fluid out of the master cylinder reservoir and refill with fresh fluid, install the pressure bleeder and pump up the pressure and bleed the brakes starting with the right rear, followed by the left front, left rear and then right front. It takes a little while to move the fluid from the MC to the right rear caliper so pay attention to how fast the initial bubbles flow through your drain hose and mentally time how long it will take at that flow rate for fluid to flow from the MC through the ABS unit and down the brake line to the caliper. Once you hit that mental mark close the bleeder and check to make sure you have sufficient brake fluid in the MC to finish bleeding that caliper. I can usually bleed the brakes on my car with 2 500 ml containers of brake fluid and have a little left over.

As for how the brakes grab or don't grab there are other things that affect that besides brake pressure. If you have a high solid pedal feel with no sponginess you don't have any air in the system. If you are changing brake pads some times you have a high hard pedal but the brakes don't feel like they aren't stopping the car. That is because the pads need to be burnished in to work better with the rotor. A few miles of city driving will usually make them grab better or you can follow GM's recommended burnishing procedure described in the OM.

Bill

 

I have always used the motive pressure bleeder as described above on several of my vehicles. However, on an old 380SL I was unable to evacuate all the air after replacing a LF caliper. I drug out my old 'unreliable' phoenix bleeder setup and pumped fluid from caliper up to the M/C. The pedal got tight as a Dixie Hatband in short order. Sometimes the Phoenix works and sometimes it doesn't. It proved invaluable this time.

 

this is how I do it as well.

You are just using the air pressure from the Motive to push the brake fluid out. Putting fluid in the Motive itself is dangerous (IMHO) since the cap doesn't seal that well which means any leak will result in you having corrosive brake fluid sprayed all over the car

 

I used to use a Motive Pressure Bleeder until I found a vacuum brake bleeder. The Capri one on Amazon is pretty slick.

 

find a gravel or dirt road/parking lot. stand on the brakes to activate abs a few times. if there is air stuck in the hcu, that will usually work it out.