What the hell happened to my clutch pedal?

[Yakinho]

Hi everyone, I've been lurking here for a while, so I finally decided to post. So yesterday I'm driving back from work and while i'm at a red light, my clutch pedal drops to the floor and stays there (had to put the flashers on and pull up the pedal with my hand to get it to the normal position)... Now when I drive, if I even rest my foot lightly on the clutch pedal, like I always have, the pedal slowly sinks to the floor. Now I assume theres something wrong with the hydraulic cylinder, but seeing as I don't have much knowledge in that area, anyones help would be appreciated.

Thanks.

[MikeE30325i]

slave cylinder probably went out.

[eyagel]

slave cylinder probably went out.

+1

[Yakinho]

Thanks, about how much is the part?

[MR 325]

Thanks, about how much is the part?

About $30.

[Mike325]

Simple to change too. Also, take off the cover under the steering wheel above your pedals. There is a master cylinder for the clutch here as well. See if you see any brake fluid in this area or on the pannel you just removed. They tend to leak as well, so it may need to be replaced with the slave.

[rede30]

either slave or master, i dont really know the differences in symptoms.

[Mr Deagle]

if brake fluid is pissing out in the drivers footwell, its the master, if its pissing out from underneath the car, its the slave, if it isnt leaking anywhere, its the master

[ANDRÜ]

I had the same problem, mine was themaster cylinder. Dont assume you need to replace the entire thing though, I bought a new master, only to find a hose had ruptured. I installed the new hose and cyinder just to be safe, and its perfect now.

[EtaSport]

Its probably the master cylinder. Exact same thing happened to me and i drove it home without the clutch. Swapped out the master cylinder and bled it and it was good to go. But check for hydraulic fluid leaks before throwing parts at it

[Garageaholic]

Yeah, the seals on the slave probably went. Any leakage anywhere?

[NC325iC]

you shouldnt rest your foot on the clutch pedal youll wear out your throwout bearing thatway

[DJB]

Both the clutch hydraulics and the brake system share the same fluid
reservoir. This might sound unwise, but the system is designed so that
they are partially isolated. The clutch system has taps about halfway
up the reservoir so that a clutch leak won't keep the brakes from
working. Similarly, the a brake system leak should not cause immediate
clutch failure. In normal operation, without leaks, the clutch won't
pump fluid into or out of reservoir, and it has a small reserve in the
reservoir tap and hose.

If the clutch stops working due to lack of brake fluid, the likely cause
is a leak in the clutch system rather than wear or just "low fluid".
You should immediately suspect a leak in the output ("slave") cylinder,
since leaks in the input ("master") cylinder are usually internal to the
cylinder and don't result in fluid loss, or cause obvious wetness on the
carpet.

Replacing the output cylinder is easy, if you can get under the car.
It's just undoing the fluid hose with a flare wrench and removing the
two mounting bolts. The fluid hose, like most of the hydraulic system,
needs an unusual size, 11,12 or 14mm. The cylinder mounting bolts are
standard 13mm ones, although you likely will need a long extension for
the top one.

Replacing the input cylinder is more awkward and time consuming,
although certainly not difficult. You can even do it without getting
under the car.

One you replace the problem part, you will need to get new fluid into
the system. The clutch system is self bleeding, at least it is once you
get a little fluid pumping. It might require a hundred or so pumps,
returning the pedal to the top of its throw by hand each time, to get it
started. Since you'll be hunched over the driver's side pumping up and
down for five minutes or so, I don't recommend doing this at a highway
rest stop at night.

Once the pedal returns on its own it takes just a few more strokes to
clear the rest of the air from the clutch lines. Any remaining tiny
bubbles will work themselves out over the next few days.

You'll find some misunderstanding on this point. The clutch system
really is self bleeding. The "bleeder valve" on the output cylinder is
there to flush old fluid, rather than bleed out air. Unlike the brake
system there are no local high points, and the volume of fluid moved is
much greater than the volume in the hose. With the brake system the
geometry forces a high point at each caliper, and the design goal is
minimal pedal travel and thus little fluid flow.

________________

My clutch input cylinder failed by tearing a seal. It quickly failed
completely once it started.

I wanted to get the car back on the road quickly, so I ordered a rebuild
kit from Advanced Auto / Parts America for about $16, planning to
replace the whole cylinder later. I expected a badly made set of
aftermarket seals, but instead it was a complete piston assembly. It
could have come off the line a minute after the original part, with the
same F-A-G brand stamp and matching casting marks. Even the machine
marks matched!

Removing the input cylinder is a PITA. I suggest taking the three
minutes to remove the driver's seat, because you are going to be
spending a lot of time removing and replacing the mounting bolts. They
are deceptively easy to see, but almost impossible to get a socket or
wrench on.

Once you have the input cylinder unbolted, uncouple the flare fitting
under the car. You can do this by just reaching under, without raising
the car. The fitting are odd sizes for BMW, 11mm and 14mm, so be
certain you have those wrenches ready. After you have the line undone
cycle the cylinder to remove as much fluid as possible, and put plastic
and then paper down to protect the carpet.

I initially uncoupled the blue supply hose inside the car. A better
approach is to uncouple it at the reservoir end. It's much easier than
it looks to snake it back, and I ended up needing to attach it to the
input cylinder before bolting it back in place.

I replaced the piston with the cylinder still inside the car, leaving
the hard pressure line running through the firewall. If you need to
remove the cylinder I'm told that the hard line will spring back to its
original shape if you pull it out in the right direction, but I didn't
want to risk mangling the line when I didn't need to.

The piston is retained by a circlip. It takes just a minute or two swap
in the new one. Then it's back to wasting time with the mounting bolts.

Note that the piston rod attaches to the pedal with an eccentric bolt.
You'll be adjusting it later, so just leave it snug for now. There is a
spec for the pedal height in Bentley, but I found it difficult to
measure. The important adjustment seems to be clutch switch. If you
get that wrong the cruise control won't activate, or will turn off for
no apparent reason.

[Mike325]

^ Nice write up there. Thanks. Just for a heads up, the brake lines do use an 11mm flair wrench and the slave nuts are 13mm.

[StereoInstaller1]

Hey mods, sticky the newb's write up!

GFJ, yO!

Luke