Soft brake pedal after running reservoir dry

[CamasM3e93]

I did a 4-corner brake pad replacement with stainless steel line installation on my m3 e93. When one of the lines was off I got called away to something else too long and the reservoir had run dry when the line was dripping.

At the end of the job I used a Schwabben pressure bleeder at 20 PSI, bleeding each caliper RR, LR, FR, FL. I bled and bled and bled to get all the air out over 2 days, but even after two days I would occasionally get a few tiny tiny tiny bubbles on one of the calipers. the pedal was incredibly firm, though......until I turned the car on and backed out of the garage. My firm pedal was gone, now very soft and I didn't dare do anything but pull it back into the garage.

I pumped the brakes with the car on for about 2 minutes to see if the pedal would firm up and it did not.

My thought is I needed to activate the ABS pump (and did not) or do a different procedure to bleed the brake master cylinder, which I understand is beneath the reservoir.

Thoughts?

[mapster37]

it would probably be a good idea at this point to bleed the brakes with the help of a second person. one pumps/holds the brake pedal and the other operates each bleeder screw...

[tdott]

You'd need to use ista/INPA/etc to activate the dsc/abs pump , for sure there is air in the system.

[CamasM3e93]

For the next guy who runs into this:

How to bleed the ABS pump manually:

Bleeding Master Cylinder on the car (generalized, not specific to e9x M3)

Gather your supplies.
Jack up the car.
Place a container or jar underneath the master cylinder's bleeder nozzle or the place for the hose attachment.
Ask your helper to slowly pump your brake pedal several times.
Have your helper press and hold down the brake pedal.
Detach the hoses connecting the brakes and the master cylinder.
Examine the brake fluid.
Reattach the hoses to the master cylinder.
Have your helper release the pedal.
Repeat until the air is out of the master cylinder.

[randrews15]

You should be able to activate the ABS pump with your Schwabeen tool. I have the same one and activate the pump every time I flush the brakes. It is likely air trapped in the ABS system and will need to be bleed properly.

[white_4door]

as others stated definitely need to do an abs brake bleed to get all the air out

[CamasM3e93]

Thanks Everyone. I ended up using the video link above that I posted to prime the ABS pump, then used my bluetooth OBDII scanner to run the car's ABS bleed routine. Brakes are working fine. I didn't end up having to prime the master cylinder, thankfully.

[exVtekGuy]

Originally Posted by CamasM3e93

Thanks Everyone. I ended up using the video link above that I posted to prime the ABS pump, then used my bluetooth OBDII scanner to run the car's ABS bleed routine. Brakes are working fine. I didn't end up having to prime the master cylinder, thankfully.

can you explain how you ran the abs bleeding process using obd scanner?

[CamasM3e93]

Originally Posted by exVtekGuy

can you explain how you ran the abs bleeding process using obd scanner?

Sure.

I bought an Autel HT200 at Walmart last summer. Looks like it has been replaced with the Autel AP200 and it's available on Amazon for $70. It is a little blue tooth device that plugs into the OBDII port and connects the BMW to my iphone via Bluetooth. Very important to have the phone set to airplane mode with WIFI and cellular connection settings on your device deactivated, using bluetooth only. The Autel device comes with one free vehicle brand software system. I have multiple brand vehicles in my garage and paid $22 for the BMW software.

Once you've got the main brake system purged of air, all you do is turn the ignition on without the motor (helps to have battery on a trickle charger), and with the car up on stands and wheels off, follow the prompts as it has you service each brake. It requires two people to pull off but essentially what the routine is doing is running the ABS pump while you have the brake line drain valve open. At the end of each wheel's routine, someone has to hold the brake pedal down while the other person closes the valve. Somehow the BMW can tell whether the routine was effective. You can also do this with a laptop connected to the car's OBDII input via a special cable and free ISTA software but that's its own set of learning.