[boba7523]

Hi guys,

I was doing my year 2 maintenance and flushed my entire brake system using the Motive pressure power bleeder but have introduced air to the last caliper because I ran out of brake fluid in the bank.

While I was releasing old fluid, I started seeing air bubbles come out and suction sound indicating there's no more fluid left in the bleeder tank.

I immediately tightened the bleeder screw and checked the brake cylinder and saw that it was empty (below minimum). Prior to starting, I made sure to fill it to "Max."

My question is, what should I do to correct this?

• Do I just fill the brake cylinder back to full and fill the bleeder tank, and finish off the flush, or would I have to start everything over again?
• Or did I cause an even more serious problem?
• I've heard to never let the brake cylinder run empty to avoid introducing air but I'm afraid that's what happened thus causing the air to come out while bleeding.
• FWIW, I never pressed the brake pedal the whole time I was doing the flush, not sure if it matters...
• Also, I'm concerned about air in the ABS system now and I'm not sure how to resolve that with ISTA+

Thanks for your help

[c0riolis]

If you introduced air in the system you need to re-bleed everything including the ABS module. Bleeding the ABS module is done via ISTA.

[tux2005]

You will need to run a lot of fluid through the system to clear the air. I ran my reservoir empty while trying to use the ABS process in ISTA after rebuilding my calipers, I think I ended up running a total of 1-1.5L through and was able to get a solid pedal again.

You will want to basically go around the car on each corner at least twice, the first time around was basically as I would for a complete fluid swap with the exception of not really trying to empty the reservoir with a pump/syringe first. Then after you finish your first cycle around, go back and check again, this time only really open the bleed screw to see if you get any air and allow a small amount to flow through if you don't see any bubbles. Also perhaps if you can easily do a test drive, you can check for a soft pedal, and then do a final check on each corner again.

Do be careful about not opening the bleed screw too far and having air come in through the threads of the bleed screw, trying to hurry the process by opening the bleed screw wide can just make everything take longer. This is when I would have hated to be working on jack stands, my QuickJack doesn't give the quickest or easiest access but it's 5-10 minutes to lift the car, take all the wheels off and then put them back on, drop the car and torque and be able to test drive.

[ggggbmw]

I totally understand how you feel. I was doing a quick caliper bleed before a track weekend, and didn't bother filling the pressure bleeder. Just watching the reservoir. Then I dropped the wrench to close the bleeder, and by the time I retrieved it from under the car and got the bleeder closed I had air in the system.

If you tried to rebleed that line without touching anything, you might have gotten lucky and just refilled the path. But if you touch the brake pedal, that's it, you are going to have to do the full ABS cycle bleed.

I had to do the ABS bleed process 4 times before I finally got rid of the soft pedal. Went through 3 liters of brake fluid. Buy something cheapish for this. (I use Pentosin LV in the off-season.) Don't be using expensive racing fluid. You can always reflush with the good stuff after the brakes are solid again.

If you have access to ISTA, it does a nice job of walking you through the whole process with illustrations. But you don't need it. Most of the better active/bi-directional scan tools with BMW aware software can do the ABS cycle flush. I use the Schwaben scan tool (a rebranded Foxwell NT510 w BMW add-on), and I'm fairly sure Bimmerlink will do it (but you should research that).

One odd thing is that the ABS bleed does not do all four corners. It just does the left front and left rear. That is why it is critical to do a full normal flush before doing the ABS flush. The 'left side only' confused me with with the scan tool at first, so I found ISTA. And it does the same thing, but with better explanations. The procedure is a bit complex. It's a good idea to go through the process without actually opening bleeders just to get the sequence down. It can help if you have two people. One to run the process and push the pedal. And one to open/close bleeders and pump/release the pressure bleeder.

Also, don't panic if the ABS flush ends with a 'failure' code. I've never gotten a 'success'. I'm not sure what isn't working, but it is still flushing the system and doing what it needs to. I'm sure I'm messing up the process somewhere and not pressing the pedal hard/soft/fast/slow enough, but it still works.

One full flush, and one ABS cycle got me 90% restored to normal. But to get the pedal completely firm again took another full bleed, and 3 more ABS cycles.

[tux2005]

Yup, definitely get some cheaper fluid as you'll go through a bunch, don't use SRF or anything like that since it's a complete waste.