Air In Clutch Lines?

[m3f_thirtysixnick]

A couple of days ago after going out to eat, on the drive home, my clutch pedal suddenly stuck to my floor after I put it in neutral to decelerate to a full stop and wait for traffic to pass for my turn... Long story short: started it in second gear with people pushing my car and just coasted at about 20mph in 2nd to my driveway where I popped it out of gear and pushed it with my family into the garage.


Guessing a few different sources could be the issue (ex: bad clutch slave/master or air in the lines from an improper bleeding at a shop) BUT the kicker for me is that my clutch now doesn't stick to the floor and it seems to feel just as fine as it did for the last year of me driving it now after sitting for a few days.


I know I'm always constantly posting semi-goofy questions, I do my research and I understand all these symptoms, but I haven't seen ANYTHING said about the clutch becoming fine again??? I've had someone pump the clutch and hold it while I watch my brake(clutch) fluid's level and nothing changes, there's no leaks from the slave or master and both externally appear okay...


Could it just be air in the lines, and I might note it was HOTTTT out (around 100 degrees easy) that expanded from the heat and got it stuck?

Another thing might I note is that the fluid is RIGHT at the max line, if not close to being above... Could that play a role in it also?


Appreciate everyone's time, and if this post angers you, or if I bother you, feel free to click off or make me feel bad as I'll take it as a grain of salt.

Enjoy your life, thx

[m3f_Chadrbrewer]

This was happening to me too, bled lines again, no help

[m3f_Braymond141]

Master is failing 100%. Replace both clutch master and slave cylinders. Take note to year specific differences on the master, there are two versions.


It is always best to replace both master and slave at the same time.

[m3f_thirtysixnick]

Master is failing 100%. Replace both clutch master and slave cylinders. Take note to year specific differences on the master, there are two versions.



It is always best to replace both master and slave at the same time.

So you're saying the clutch working now means nothing? Theoretically speaking, what would driving do and how long would it take for it to stick again???



Plan to replace both master and slave. Any specific DIY's beside Pelican?

[m3f_Braymond141]

Your symptom describes a failing master to a T. Nobody can answer the rate of reoccurring loss of use, it varies. I’ve dealt with it lasting a week and then failing every 20mins of use.

[m3f_thirtysixnick]

Your symptom describes a failing master to a T. Nobody can answer the rate of reoccurring loss of use, it varies. I’ve dealt with it lasting a week and then failing every 20mins of use.

Would it be solid enough for me to back it up 30ft to wash and pull back in? Thing is dirty and I don't like it sitting dirty


Don't plan to daily it until replaced, but am curious how far I could take it also.... Probably shouldn't try haha


Just recently got rearended (100% not the one at fault btw) in the 330Ci I daily while the M3 is being a turd so now I have to try and snag my sisters camry to go to work and such...

Hoping I can get at least enough money for a low mileage NA Miata out of it...

[m3f_Braymond141]

That's up to you.

[m3f_Jrrrrrrr]

This is a case of a failing clutch hydraulic cylinder(s). Whether it is the master or slave doesn't matter much, as both really should be considered preventative maintenance if you have to record of them being replaced. The reason the clutch firmness and actuation returns after the car sits is because the clutch hydraulic circuit is "self bleeding," in that air introduced into the system by a failing cylinder will rise and exit to the brake master cylinder reservoir with time. Repeated pumping of the pedal will also purge the air, but in this case, new air is probably being introduced past the failing cylinder seals and causing a net rise in air in the system.



There are many DIYs out there on replacing both cylinders. Go with genuine BMW or F.A.G. for these semi-critical parts. I've personally had a Febi slave fail almost immediately and spew brake fluid all up in my bellhousing, so I learned my lesson.



For other tips, I highly recommend using a pressure bleeder to bleed the clutch hydraulics when you get the new cylinders installed. You can build your own pressure bleeder with like $20 in hardware store parts, and the cost is well worth it in terms of time and frustration saved. Strongly consider the clutch restrictor delete mod (and replacement slave-cylinder hose) if it isn't already done. Strongly consider installing bronze or delrin bushings for the clutch and brake pedals, or order a new clutch pedal if you want to go with OEM plastic bushings. Replace the brake-light switch if you have been getting any intermittent "brake circuit" warnings on the OBC. There is no easier time to do pedal bushings or the brake-light switch than when you're already in there doing the clutch master cylinder.

[m3f_thirtysixnick]

This is a case of a failing clutch hydraulic cylinder(s). Whether it is the master or slave doesn't matter much, as both really should be considered preventative maintenance if you have to record of them being replaced. The reason the clutch firmness and actuation returns after the car sits is because the clutch hydraulic circuit is "self bleeding," in that air introduced into the system by a failing cylinder will rise and exit to the brake master cylinder reservoir with time. Repeated pumping of the pedal will also purge the air, but in this case, new air is probably being introduced past the failing cylinder seals and causing a net rise in air in the system.



There are many DIYs out there on replacing both cylinders. Go with genuine BMW or F.A.G. for these semi-critical parts. I've personally had a Febi slave fail almost immediately and spew brake fluid all up in my bellhousing, so I learned my lesson.



For other tips, I highly recommend using a pressure bleeder to bleed the clutch hydraulics when you get the new cylinders installed. You can build your own pressure bleeder with like $20 in hardware store parts, and the cost is well worth it in terms of time and frustration saved. Strongly consider the clutch restrictor delete mod (and replacement slave-cylinder hose) if it isn't already done. Strongly consider installing bronze or delrin bushings for the clutch and brake pedals, or order a new clutch pedal if you want to go with OEM plastic bushings. Replace the brake-light switch if you have been getting any intermittent "brake circuit" warnings on the OBC. There is no easier time to do pedal bushings or the brake-light switch than when you're already in there doing the clutch master cylinder.

Wow, appreciate the detailed info.

Super cool to understand what's actually going wrong.



I'll probably do the brake light switch and possibly a CDV delete and maybe replacing the bushings for the clutch/brake pedals.

My clutch pedal is pretty creaky/semi-wobbly if you don't push it in fast and I'm guessing bushings could be a part of the cause??? I haven't looked up the creaking, but I do know it's a common problem that I've just overlooked as it doesn't creak for me because I rarely make it make the noise with how fluent my clutch movements have become lol.



Also, with the air in the system, what are you opinions on driving it? As I said, I don't plan to daily it, but I'm just wondering how far/long it could be driven like this. Estimates are fun to make, and I'm not trying to figure out, but I'd just like to know for possible future reference if anything were to go wrong in the future or if I HAD to drive it now for an emergency.

[m3f_Chadrbrewer]

Mine would be fine in the morning, I would get to where I need to be, then I would go to leave the clutch would hit the floor. A couple miles did it for me.

[m3f_thirtysixnick]

Mine would be fine in the morning, I would get to where I need to be, then I would go to leave the clutch would hit the floor. A couple miles did it for me.

How long would you let it sit before you needed to leave?



Guessing mine is very similar, but I did drive probably 4/5 miles after I washed it a couple days ago and nothing acted up or felt weird at the end of the drive.



Theoretically if it's not sticking when you're done driving, it shouldn't stick (or at least for a little) the next time you start it up to leave, right?

[m3f_englishtom1596q]

Doesn't sound like you're going to listen to the advice given so just drive it as much as you want. It will fail again when it's most inconvenient and you'll have to limp it home again or pay for a tow truck. I know what I would do and did (because it happened to me) and that's order the parts and let the car sit there until it's fixed.

[m3f_propchef]

Maybe OP should consider an auto swap.


Sent from my grow room

[m3f_Chadrbrewer]

How long would you let it sit before you needed to leave?



Guessing mine is very similar, but I did drive probably 4/5 miles after I washed it a couple days ago and nothing acted up or felt weird at the end of the drive.



Theoretically if it's not sticking when you're done driving, it shouldn't stick (or at least for a little) the next time you start it up to leave, right?

overnight typically, once it hit the floor it was done. Ironically mine started doing it after i went through the car wash too.

[m3f_Chadrbrewer]

i have since replaced the master and slave, and new clutch lines, all is better in my world