Spongy Brakes after Flush

[DRiFT_645]

Hey guys,
Got an issue that has me confused.

A month ago, I had my brakes flushed at an independent shop. Within a few days, i noticed the brakes feel spongy, and sometimes need to be pumped. This got worse.

I took the car back and they redid the entire procedure. Problem persisted.

Took the car to BMW. They flushed it again, found air in one front caliper and one rear. Brakes worked well for a couple days and the problem came back.

Took the car back to BMW. They said they’ll flush it again because air can sometimes be trapped. They also did a more intense bleed of the DSC. Charged an extra hour too. M technician test drove the car and said it’s great

Within 5 minutes of picking up the car, I noticed the problem is still there, though not as bad as before. I have to push the brake down a lot further for them to work.

Common issue throughout is brake pressure decreases even when holding brake (car begins to roll).

BMW now suspects failing master. Wanted your opinions. How can all this (and a master) fail after a routine flush? Brakes were PERFECT prior to starting this process

Thx in advance.

[M5Rick]

Can only think the indy did something wrong in the initial brake bleed,perhaps pushing the pedal too quickly and hard or it's just coincidence that the m/c is failing.If the car has a lot of miles then it's possible, it can happen.Alternitively the brake booster/diaphragm enclosure has an air leak which can cause those symptoms.Is there hissing when holding brake?

[DRiFT_645]

No sounds when holding the brake.

Car has relatively low miles on it... 100,000km (62K miles).

I can't see how a flush would cause the master to fail... BMW dealer said if they use too much pressure... indie shop says they didn't pump the fluid in.

Indie shop is a good friend of mine, owns the same car himself and did the same procedure to his car 6 months ago with no issue.

[mrtt]

I'm sure the tech checked for leaks on each wheel and brake lines? Maybe it's a coincidence but master cylinder seals do go bad if you let air in.

[DRiFT_645]

Thanks for the tips guys. Car goes back tomorrow. If they suggest the master, which I suspect they will based on our conversation on Friday, I'll go ahead with it. I just hope the problem isn't still there after they replace it!

[technician117]

A strange one for sure, but things do happen.

I plan to flush mine in the next few weeks. Keep us posted!

[SapphireM5]

How did you make out? Usually if you hold steady pressure on the brake pedal and the pedal drifts to the floor it could be a bad master cylinder. If you do the same and it only compresses some, it could be air in the lines.

Really strange how it started right after the flush. I doubt the master was damaged during the flush. Either there's a bleeder leaking allowing fluid /air transfer past it or there's still air in the lines. If they got air in the lines it could be trapped in the DSC even though I know you said they did that. ITSA has a whole procedure to do each caliper at a time, it flushes one line at a time while activating the DSC/Abs pump.

[DRiFT_645]

It’s an odd one for sure. Drove the car yesterday and today and the brakes behaved perfectly fine. Tech thinks it might have been air. Keeping an eye on it over the coming weeks but for now, somehow it’s returned to normal.

[bgalex]

Bringing an old thread back but Im having a spongy brake feel as well, my buddy has the same car as mine and his brakes bite within the first 5% of brake press.. Where as mine i need to press at least 30-40% until I feel any bite I have brand new pads and rotors

[DRiFT_645]

Problem came back today. I’ve noticed the problem returns around really hot weather.

Dealer last time said my rotors need replacement. They’re suggesting changing the brakes first. I don’t see how it would cause the pedal to drop down. They don’t want to touch the master til “brakes are in spec”.

[M5Rick]

Originally Posted by DRiFT_645

Problem came back today. I’ve noticed the problem returns around really hot weather.

Dealer last time said my rotors need replacement. They’re suggesting changing the brakes first. I don’t see how it would cause the pedal to drop down. They don’t want to touch the master til “brakes are in spec”.

Watch out they may be taking you for a ride,I'd go to an indy brake specialist for a power bleed and a second opinion.

[DRiFT_645]

I agree. Only reason I’m going with it is that my rotors are ridged now (original since purchase) and I’m at 120,000km.

I have a suspicion it’s the master.

[M5Rick]

Originally Posted by DRiFT_645

I agree. Only reason I’m going with it is that my rotors are ridged now (original since purchase) and I’m at 120,000km.

I have a suspicion it’s the master.

Wow that's 74500 miles nice to know they lasted that long, mines half that mileage and just a little lipped.
You have to measure the minimum thickness of discs front and back and if below min then yes they need changing.

[DRiFT_645]

Agreed Rick. But would that explain the spongy pedal (Sinks to the floor when braking, requiring pumping to stabilize pressure)?

I just don’t see the connection. I think I need rotors and possibly a master.

[M5Rick]

The problem started after the indy bled them, so yeah it looks somethings up with the master if it persists and it looks like that unless a bleed screw is failing somewhere on a caliper but that's unlikely.

[SpeedProtocol]

once you have a lip these rotors are almost done.

[Solo_M_Tech]

You can have trapped air in a master cylinder remain after a failed flush due to the piston bores in the cylinder trapping between the primary and secondary pressure chambers. The master cylinder needs to be bench bleed ( the messy way is a pressure bleeder, and crack the lines coming out of the master cylinder until clean fluid comes out). or removed it and actually bench bleed it. Only after that is done and the master is completely air free, the rest of the system can be bleed properly. This will solve the problem.