Bad master cylinder?

[eacmen]

FYI If you end up not installing the MC may want to hold onto it as they are hard to find right now.

[eacmen]

Other way around!

The first half is soft then it firms up. Like it needs a really good bleeding! I think you guys may have been right about air in the lines. Still unsure how on earth it got there as I didn’t touch the braking system... but now I’m motivated to do a bleeding (something I should’ve done to begin with).

Yeah bleeding it to see what happens is way cheaper than the $600 MC!

If with the engine off the pedal gets firm and you can keep constant pressure and the pedal does not sink then the MC is okay.

Soft pedal at beginning of travel is air.

[SteelGreyM]

So with the engine on the brake pedal is firm for the first half of the pedal travel then gets soft?

I think this is due to the vac assist. With the engine off you can’t apply enough force to cause the pedal to go soft.

Other way around!

The first half is soft then it firms up. Like it needs a really good bleeding! I think you guys may have been right about air in the lines. Still unsure how on earth it got there as I didn’t touch the braking system... but now I’m motivated to do a bleeding (something I should’ve done to begin with).

[eacmen]

Ok so update.

I’ve been driving the car around for a week now. Put 2xx miles on it. The brake pedal is hard as a rock with the engine off. Engine on the brake pedal is firm 50% of the way through.

I literally haven’t even touched the braking system as my master cylinder just arrived.

Sooo am I looking at air in the lines or do I still need to swap that thing out.

So with the engine on the brake pedal is firm for the first half of the pedal travel then gets soft?

I think this is due to the vac assist. With the engine off you can’t apply enough force to cause the pedal to go soft.

[SteelGreyM]

Ok so update.

I’ve been driving the car around for a week now. Put 2xx miles on it. The brake pedal is hard as a rock with the engine off. Engine on the brake pedal is firm 50% of the way through.

I literally haven’t even touched the braking system as my master cylinder just arrived.

Sooo am I looking at air in the lines or do I still need to swap that thing out.

[Kdubski]

Have the exact same problem after an engine rebuild. The air in MC noise appeared 300 miles after putting motor in. Dealt with it during break in and now that spring is here going to look into it.

Could it just be a coincidence or maybe assembly error?

[liam821]

Yeah, if you have air in the ABS system you need to use INPA to run through the brake bleed procedure.

Will do. Starting to understand where “break my wallet” comes from...

See you just need a whole other e46m3 as a parts car............

[eacmen]

I’m not sure if my cable is bad or not but I can’t communicate with a bunch of modules...

Make sure pins seven and eight are shorted

[SteelGreyM]

INPA can definitely do it. Just did it last week on my car.

Click the activate button in the dsc menu and there should be a button that says something about the abs pump (sorry about the vague description, but I'd need to hook up my computer to my car to tell you exactly what to click). It'll ask you to press the brake pedal at least 80% (I think) and it'll actuate the pump.

I’m not sure if my cable is bad or not but I can’t communicate with a bunch of modules...

[heinzboehmer]

INPA can definitely do it. Just did it last week on my car.

Click the activate button in the dsc menu and there should be a button that says something about the abs pump (sorry about the vague description, but I'd need to hook up my computer to my car to tell you exactly what to click). It'll ask you to press the brake pedal at least 80% (I think) and it'll actuate the pump.

[bigjae46]

How do you go about actuating the ABS pump? My INPA only activates a few features on the M3. On the non M it will activate everything and run vanos tests too...

May need to take it to a shop and have them hook up their computers to do a proper bleeding.

I’m pretty sure I used INPA. IIRC, I had the ignition on and pushed the button.


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[eacmen]

How do you go about actuating the ABS pump? My INPA only activates a few features on the M3. On the non M it will activate everything and run vanos tests too...

May need to take it to a shop and have them hook up their computers to do a proper bleeding.

I use the foxwell 510 scan tool that schwaben resells. You can do it with DIS as well though.

[bigjae46]

Did you use a pressure blender or two person?

How much total fluid did you need to push through the system before it was bled?

Crack the bleeders while actuating the ABS pump?

I used a pressure bleeder. I think I used 2 qts. I think I spilled a good amount trying to bench bleed it...what a fiasco. Didn’t have the right fittings. Need the right fittings.

If you use a bleeder fitting, just leave it open and keep pumping the piston by hand until no more bubbles circulate. Don’t need to open and close.

Once I installed the MC it didn’t take long the bleed all of the air out. If you didn’t bench bleed then I’d imaging it would take a long time to get the air out. I spent more time bench bleeding than doing the rest of the install.


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[JudahJD904]

My master brake cylinder was fine before sitting for 3 years. I came back, started it up, and the pedal went to the floor with no ABS and only the front rotors working with no warning lights except for DSC. I had a shop flush the brake fluid to make sure it wasn’t air or old brake fluid, but it ended up being a faulty master cylinder. Good luck with getting yours fixed.

[SteelGreyM]

Did you use a pressure blender or two person?

How much total fluid did you need to push through the system before it was bled?

Crack the bleeders while actuating the ABS pump?

How do you go about actuating the ABS pump? My INPA only activates a few features on the M3. On the non M it will activate everything and run vanos tests too...

May need to take it to a shop and have them hook up their computers to do a proper bleeding.