Brake flush question...
 

I have a Motive Power Bleeder (or I should say I borrowed one). Everything I have seen online says to leave the existing fluid in and pump it out as you are putting new fluid in.


...but in talking with another friend who does track days - he says he pumps all the OLD fluid OUT FIRST. Then pumps in the new fluid.

Which is correct? Or is either OK? This is my first go at this so the easier the better so long as I don't screw up my brakes.
;)

The downside with flushing out the old fluid and not putting in new fluid is you have to do double the work. With this method, you will just fill all the lines with air, and do another "flush" to replace the air with the new fluid. The upside is that you can be assured that you have brand new fluid in all your lines.

If you do what most people do, which is just empty the reservoir and put in new fluid, you just wait until you see clean fluid coming out of the valves. I guess the downside here is that there is a chance you can have the old and new fluid mix, unless you flush out a whole lot of fluid.

I would just put two new bottles of fluid in the motiv and just bleed until new fluid comes out. I will say that if you do take out all the old fluid from the reservior, make sure you do not introduce air into the system... It will be a bi#$h to get all the air out of the lines. Ask me how I know...

That's exactly what I'm afraid of... I'm using the Motul RBF600 and I guess it's the same color as the stock fluid so seeing when the new fluid starts might be a little challenging. But I only have 3 bottles of fluid and I would hate to drain everything and run out trying to get all the bubbles out if I drained it first...

I'm just going to stick with leaving the old in this time.

I ended up using superblue so I could tell when the old fluid was out and the new fluid was in. I drained half of the old fluid out of the reservoir and put the new fluid in the power bleeder. Next flush I'll switch to a different color so I can tell when the new fluid is in.

Generally, we use the "two person" method, and will bleed one corner till clean fluid is coming out. Then we'll do the other three. Then, we'll do one more round, to make sure there's no contaminated fluid left.

Cheap and effective; you can bleed with 500ML if you're careful.

I don't like superblue because it is hard to flush it out later. May stain reservoir

How do you know? I take it you have been through this experience, what did you have to do to get the air out?

I changed the fluid by removing the old fluid from the reservoir first and I think I have introduced air into the cylinder.

In the manual it says you have to remove the two brake lines from the cylinder, press and hold the pedal, block the two holes with your fingers, then release the pedal. Repeat 3 to 4 times.

Any help would be most appreciated.

I just had my dealer do it; cost me around $115 including Motul RBF600 fluid (yes, my dealer stocks it!) for a full flush PLUS cycling the ABS system to get the old fluid out of that as well.

The last time I did a full flush on my CTS-V, I could not get the air out of the ABS system for the life of me because I didnt keep the reservoir completely filled during the flush, causing air to get into the system, and it was a pain in the ass to get it out.

I flushed two more times and gave up
Took it to my mechanic who hooked it up
To a machine which bled the ABS as well

Took them another 3 hrs to get air out

How do you know if there's air in the ABS?

don't know... That is what my mechanic told me!

No matter how much flushing you do, theres no air bubbles coming out, but the pedal still feels spongy. That's how I knew on my old car. I took it to the GM dealer who hooked it up to the computer, cycled the ABS system, and voila.

I used to drain the reservoir by simply sucking out braking fluid out of the top (with a manual piston pump) and then flush the entire system with new fluid. (Such that not the entire old brake fluid in the reservoir would be flushed through the system.)
I've never heard or seen anybody who purposely would get air into the braking system (this is something you would always try to avoid).