If you never let the fluid level drop; it doesn't seem like there should have been an issue as there wouldn't be an opportunity to introduce air into the system.

Opening the bleeders to allow the caliper to retract is always a good idea - shouldn't have caused an issue either. :dunno:

Other than cycling the ABS unit I am not sure what else to try.

Only thing I can think is there are two sections in the reservoir. Maybe I was watching the level, but the rear section I didn't see and it ran dry. I had a pressure bleeder with lots of fluid connected and it never ran empty. One bleed already with the software and no luck. Pedal still sinks with engine on, mush, but doesn't sink with engine off.

Uh oh...that is exactly what I did. I hate to say it, but I think you are in the same situation. Bleed cycle pump bleed cycle pump, repeat many, many times :(

Hi Ashaman - to clarify, did you let half the reservoir go empty as I suspect I may have? Or just the symptoms are the same? Approximately how many cycles were required to fix?

I still can't see how it went empty, because the fluid I was flushing out was a different colour than the new stuff. I ran a lot through and it all came out clean. Unless I introduced a large air pocket right at the end of it.

No good explanation for how it's operating on vs off though. No one I talk to can explain why it is like it is.

Thanks.

Yes, I let it go empty accidentally. It sounds similar. The pedal was really weird feeling; sometimes almost "fluttery", but when it built resistance it would creep down to the floor. If I had not known the history, I would have suspected a bad master cylinder.

I had to cycle it LIKE FREAKIN' CRAZY. Seriously, I just kept running a circle doing one wheel at a time. About the time I thought I wasn't getting anywhere a huge stream of bubble came out of the passenger's right, and it was all improvement from there. I drove it around for a day or two, then did another go around just for the heck of it, brakes are amazing now.

I really used all methods included in this thread; pumping/releasing with the engine on and with it off. Pressing the pedal to the floor, opening a bleeder with the tube submerged in fluid, releasing; Pumping with it open and submerged. Couldn't really tell you which if any of those helped, but the the cycling under pressure seemed to really be the key. Lots and LOTS of cycling under pressure. Well, that and a truckload of persistence; beyond what I thought was reasonable :)

After reading this thread I wanted to make sure I avoided introducing air into the system (I flushed my brakes last weekend)

I did one caliper at a time and disconnected the pressure bleeder and filled the reservoir back-up between each! :)


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I did a gravity bleed on mine. No issues. I did keep the fluid topped the brim throughout though.

The right rear took forever since that is the one I used to drain the res.

Garrett I think that's the ticket. I think the pressure bleeder I'm using is part the culprit (Motiv). When I get it back, I'll try using it to pressurize only, not pressurize AND fill. So what I'll do is fill reservoir full, then pressurize, then bleed a corner, release pressure, fill, add pressure, bleed - and repeat until that corner is good. I won't rely on the bleeder to maintain the level as I suspect it introduces bubbles when you fill it with fluid and/or pressurize it.

My own experience says you are correct. Use just the tank for pressure only, filling up the reservoir each time and you will be fine. I have used this procedure on approx five BMW models now and all end up perfect.
The right rear (passenger rear) has the longest run from the reservoir so take your time, bleed it completely as the fluid has to run through the master, ABS system, down the entire tube lines to the caliper. The dirt, scale, and dis colored fluid will make you think you taped into a used oil drum some where, but don't worry it will clear out after awhile. Just keep the pressure to approx 20 psi, reservoir filled and you will be ok.
I use the foot pedal method at the end to confirm all is functional and to release any "locked" air bubbles in the system. It requires a helper who can follow simple instructions.:confused:

Plan on every two years and you should be ok unless you introduce water or race the X.
Good luck and keep the wheels right side up

It's recommended that the res be pumped out/turkey bastered. If the res fluid is old/wet you dont want to push it thru the system.

The entire purpose of brake system flushing is keeping moisture exposure to a minimum.