Flushed Clutch - Really Surprised

[calvin1]

One thing I noticed by accident on my new-to-me '94 BMW 530i is that the fluid in the reservoir for the clutch was unbelievable grungy. There were all sorts of chunks and flakes floating in it. I siphoned out the reservoir and then refilled and flushed about half a quart of DOT4 fluid through the system. I'm just stunned at the difference between before and after. I wasn't really even expecting to notice a difference. I just wanted to get the fluid freshened up.

Before the clutch was just a little on the heavy side but nothing out of the ordinary. Now after pushing through all that nasty fluid the pedal is very light, about as light as a what you'd get from a gas pedal. Is this usual for fresh versus very bad fluid? Does brake fluid viscosity increase noticeably as it goes bad?

 

[Ken42]

Brake fluid collects water which compresses.

 

[calvin1]

I wonder if brake fluid gets less slippery as it degrades. Anyone know?

 

[unDummy]

Water can't be too good of a lube. And, seals probably feel a little better with pure brake fluid and not mud.

Some dot4's are a little thinner than dot3 brake fluid. So, you might just find it easier to use the pedal. Try 5.1 next time.

Clutch fluid, like brake fluid, needs to be bled every 2 years. If it is too much of a hassle, a siphon/refill every now & then will refresh the fluid.

 

[flyingtoaster]

The junk is your seals deteriorating. I went too long on my clutch fluid and ended up having to replace my master cylinder. First, I tried changing the fluid, but it was opaque in another 2 weeks.

This is what the MC looks like from the footwell. If the area labeled "A" is black and gooey or dripping brake fluid onto the carpet, you have a problem.

 

[calvin1]

I haven't notice that it loses fluid but I'm keeping my fingers crossed. It's a good thing there's a tranny shop within pushing distance. I don't think I could do that job myself.

 

[flyingtoaster]

Mine wasn't losing fluid either. But if you can flush the lines, replacing the MC is not much more involved.

Still, it may not be the problem. You could still have air in the clutch lines.

 

[dparm]

Originally Posted By: calvin1
I wonder if brake fluid gets less slippery as it degrades. Anyone know?



Viscosity would change, yes. That's another reason why brake fluid must be changed. If the velocity changes it will interfere with ABS/ESP operation.

 

[calvin1]

Originally Posted By: flyingtoaster
Mine wasn't losing fluid either. But if you can flush the lines, replacing the MC is not much more involved.

Still, it may not be the problem. You could still have air in the clutch lines.
I'm pretty certain there's still a small bubble in the slave. Ze engineer zat did zis deezein haz ze bleeder pointing down. I'm trying to decide whether I care enough to unmount it so I can bleed it fully or just live with it.

 

[onion]

I don't know about a beemer, but I wasn't able to get all the air bled out of my F150's hydraulic clutch when I replaced the master cylinder. But after driving it around for a couple days, the air worked itself out.

 

[Astro14]

On my old Mercedes, the clutch was supposed to be pressure bled from the slave cylinder...bleed from the bottom up...unlike brakes...

Possible your beemer is the same and that's why the bleeder is on the bottom...

Got a Mityvac or pressure bleeder?

 

[calvin1]

Originally Posted By: Astro14
On my old Mercedes, the clutch was supposed to be pressure bled from the slave cylinder...bleed from the bottom up...unlike brakes...

Possible your beemer is the same and that's why the bleeder is on the bottom...

Got a Mityvac or pressure bleeder?

I've been thinking about getting a bleeder for a while so maybe this is a good excuse. Harbor Freight has an outlet nearby so maybe I'll see if they have something good enough for occasional use.

The bleeder port is at the top but it points down at a 45* angle when it's mounted so there will always be a tiny bubble above it unless you unmount it, rotate it for bleeding and then remount it. I'm going to let it sit for a few days. The fluid was aerated from the test drive so I want all the foam to get back into a single bubble before I crack it open. My driveway has about a 5* grade and I'm hoping that putting it up on one ramp across the grade I'll be able to get a little more of the air out and then call it good.

It's completely drivable now but it could be better.

 

[Torino]

Synthetic brake fluid really improves the pedal action..It lasts longer too. John--Las Vegas.

 

[Craig in Canada]

Originally Posted By: Astro14
On my old Mercedes, the clutch was supposed to be pressure bled from the slave cylinder...bleed from the bottom up...unlike brakes...

Possible your beemer is the same and that's why the bleeder is on the bottom...



Yep, my E39 bleeds from the slave. Any air in the master which doesn't come through travels up to the reservoir and bubbles up.

Push the pedal, open the bleeder, clutch spring forces fluid out, close bleeder, raise pedal. Repeat. Don't raise the pedal with the bleeder open or you'll need another half quart of brake fluid to fix it.

 

[Craig in Canada]

Originally Posted By: Torino
Synthetic brake fluid really improves the pedal action..It lasts longer too. John--Las Vegas.


All brake fluids are "synthetic". This is not to say that they all have the same properties.

 

[mechtech2]

Water will not compress with clutch system pressure.
[Maybe on some theoretical science paper.]
But water and crud certainly were causing you clutch grief. I'd turkey baster it every week until it stays clear.
Of course a bleedh is a good move, but this will help in a slower way.

 

[Ken2]

Originally Posted By: Ken42
Brake fluid collects water which compresses.

The problem in brake systems is that under emergency braking the fluid gets so hot that the water in the fluid vaporizes. Steam certainly does compress and you crash.

 

[CBR.worm]

Clutch fluid frequently gets nasty faster than brake fluid despite it's easier life. I think it is due to the flow volume of one vs the other. It is common for new (or old) vehicles to have clutch fluid get nasty very quickly.

 

[mechtech2]

Water, water vapor, and steam are different.

 

[flyingtoaster]

I replaced both my MC and SC a few weeks ago and my clutch fluid is already dark. Is this the new seals breaking in, or should I replace the rubber brake line too?