Bleeding the brake master cylinder

[Flow]

Hey Everyone !

I need some help.
I believe I have air in the master cylinder, and I'm not sure how to bleed it while it is in the car, without introducing too much air in the system.
I have INPA to bleed the ABS unit if needed.

Symptoms are, in my opinion, spongy brake pedal, and when I push quickly on the brake pedal I have a like "bubbling / air circulation" noise. I can film that to have you hear it.

Any input is appreciated

Thanks. Florian.

[Slideways]

Are you using a power bleeder or two person method? Motive power bleeder and cycling the ABS with INPA should get all the air out.

[Flow]

Motive power bleeder + 2 person method.
After the hibernation of my car I really circulated a lot of brake fluid through the system and cycled the ABS a couple of times to really get all the air out.
Will this really get all the air out of the master cylinder ?

[Flow]

Some more food for thoughts

Here is the sound of my brake pedal.
Pumping on it doesn't make it harder, the feeling doesn't change. Car brakes well but the pedal requires qui a bit more force than a modern car. Maybe that is normal ?

https://youtube.com/shorts/T6m4mVDA7Lg?si=qNZgL32nuYkKiVjd

Here are some measurements done on INPA

Braking hard



Braking with all my chicken legs might




Can you please share your measurements to see if my car is normal ?

Thanks in advance !

[Slideways]

Does the pedal go firm if you pump the pedal with the engine off?

[Flow]

Does the pedal go firm if you pump the pedal with the engine off?

Yes

[Slideways]

It sounds like the pedal is making a hissing sound. My first thought was a faulty brake booster - https://www.e46fanatics.com/threads/...brake.1009523/

You did say the car has been sitting for a while and these components are 20+ years old at this point.

To my knowledge, the only other thing there is the master cylinder and I'd expect you to see fluid leaking somewhere if a seal went bad.

[sapote]

+1 on booster vac leaking sound, but this should cause lean codes and high fuel trim at idling.
OP, any engine codes?

[sapote]

After the hibernation of my car

how long? People should step on the pedal hard (assume engine off) to move all the brake system pistons (master and calipers) to prevent the piston seals from bonding to the cylinder, every 6 month.

damaged master rear seal can lead to booster suck in brake fuid from master, then destroy the booster too.

[Flow]

Hey sapote !
Thanks for your feedback.
No engine codes, it runs perfectly.
Car sat still for 8 years in a climate controlled garage. Brake fluid being sucked into the booster makes a lot of sense. Expensive parts to replace though
Is there a way to get a definitive diagnostic on this ? I guess brake fluid would get sucked into the engine which would "suck" ?

[eacmen]

Ideally using the two person method with the power brake bleeder and scan tool to actuate the ABS will work best.

If you follow the ISTA method it will tell you to have someone pump up the brakes while you actuate ABS while cracking the bleed screw.

[Flow]

Yes I did that indeed, and the brakes are well bled I believe.
The more I think of it, the more what sapote describes makes sense.
Now I need to spend the €1k to change the booster + master cylinder

[Flow]

Just bought a brand new booster and master cylinder.
I was never convinced about the brake pedal feel, I hope this will sort it. I had it already replaced once with a used unit, going the brand new route now to just be certain it is all good.

Now when installing the new master cylinder, I need to make sure it is bled properly and not ruin it from the start.

I see there are some master brake cylinders for like $100 on ebay, brand new, and from BMW it's like $600.
What's the deal with that ? I won't play the aftermarket game on that item, but that made me curious

eBay

[eacmen]

If I were you I would get a cheap bench bleed kit to bleed the MC before you install it.

[Flow]

I'll buy that too, thanks.
I'll watch videos of how to install that.