Clutch Fluid Reservoir Partition and Bleeding

[AKA_951]

Yet another clutch bleeding problem. You would think Porsche would have designed a system to be bled. No, they had to combine the reservoirs and introduce a partition so a leaky clutch would not let your brakes run dry. All that aside, I don't have a power bleeder, and I'm not planning on buying one (maybe). But please don't just comment "Buy a power bleeder", because this is a technical discussion.

I cannot for the life of me find the hole that lets brake fluid spill from one side to the other. Is it as small as the sensor cup hole? I've put my fingers in the reservoir and can't feel the tipping point.

I'm bleeding the clutch. I fill the reservoir with fluid (as much as possible). I pump the pedal and crack the master cylinder line, which bleeds air out of the master cylinder threads. When fluid starts flowing out of the threads, I know most of the air is out of the cylinder. Moving to the bottom, I crack the slave cylinder while somebody pumps. I get a little bit of froth and then fluid. I assume I'm done. I have a pedal, which is good. A couple weeks later the pedal feels softer. I noticed that the line between the master cylinder and flexible line creates a high point to trap air during bleeding. Is the fluid viscus enough or the line small enough to push bubbles downward (like bleeding the brakes). Or, is the inner diameter of that flexible line running to the slave cylinder too large allowing bubbles to move up faster than I can pump fluid out of the slave cylinder nipple. If this is the case, the ONLY way to bleed is to increase fluid velocity (i.e. power bleed) or bleed bottom up using a grease gun to increase fluid velocity. This in turn defies gravity by forcing bubbles down as they are stuck in the fluid.

Is anybody else feeling this way? I think reverse bleeding is the way to go, but the master cylinder HAS to be pointing down (back of car raised). Once bubbles make it in there, fluid velocity alone won't push them to the reservoir because the cylinder is larger than the line.

Just a thought. I'd like to drive my car sooner of later

[Turbo17]

Originally Posted by AKA_951

Yet another clutch bleeding problem. You would think Porsche would have designed a system to be bled. No, they had to combine the reservoirs and introduce a partition so a leaky clutch would not let your brakes run dry. All that aside, I don't have a power bleeder, and I'm not planning on buying one (maybe). But please don't just comment "Buy a power bleeder", because this is a technical discussion.

I made one out of a couple of mayonnaise jars some brass tubing stuck into them and some plastic flexible tubing. A piece of innertube hose-clamped over the brake reservoir with brass tubing shoe-goo glued in finished it off. I would pressurize the bottle with a few psi air from my compressor to force fluid through. It helped me and only cost a buck or two.

I cannot for the life of me find the hole that lets brake fluid spill from one side to the other. Is it as small as the sensor cup hole? I've put my fingers in the reservoir and can't feel the tipping point.

The entire passenger side wall of the brake reservoir is a double wall. Fluid flows into that side and between the walls to get to the clutch reservoir half. The inner double wall isn't very high in the brake reservoir half (near the rear of the car), so fluid flows over it to get into the double wall.

I'm bleeding the clutch. I fill the reservoir with fluid (as much as possible). I pump the pedal and crack the master cylinder line, which bleeds air out of the master cylinder threads. When fluid starts flowing out of the threads, I know most of the air is out of the cylinder. Moving to the bottom, I crack the slave cylinder while somebody pumps. I get a little bit of froth and then fluid. I assume I'm done. I have a pedal, which is good.

If it's hard I would think it's bled, although I had trouble doing what you described.

A couple weeks later the pedal feels softer. I noticed that the line between the master cylinder and flexible line creates a high point to trap air during bleeding.

Someone suggested to me to bleed air out at that point. I tried it, but it didn't completely work.

Is the fluid viscus enough or the line small enough to push bubbles downward (like bleeding the brakes). Or, is the inner diameter of that flexible line running to the slave cylinder too large allowing bubbles to move up faster than I can pump fluid out of the slave cylinder nipple. If this is the case, the ONLY way to bleed is to increase fluid velocity (i.e. power bleed) or bleed bottom up using a grease gun to increase fluid velocity. This in turn defies gravity by forcing bubbles down as they are stuck in the fluid.

Some have had success pedal bleeding. I didn't. Raising the rear end helps. The slave cylinder has to get the rear end high enough to let bubbles out.

Is anybody else feeling this way? I think reverse bleeding is the way to go, but the master cylinder HAS to be pointing down (back of car raised). Once bubbles make it in there, fluid velocity alone won't push them to the reservoir because the cylinder is larger than the line.

I saw a video on bleeding a similar system on a BMW - they used pressure from the bottom ( a clean/new pump-type oil can.) It didn't work either.

This worked for me - a half full mayonnaise jar of fluid with a long and short brass tube glued in the top (I set this bottle on the fuse/relay box when bleeding). The long tube extends is below the fluid surface, the short above it. The short tubing is connected to my air gun at very very low pressure.

The long tube is connected to the fluid reservoir top - sealed with a rubber sheet hose clamped on and having a short brass tube through it sealed with shoe-goo or silicone or whatever. I fill the reservoir very full. That seal was the hardest to make. I used a hair dryer to heat the rubber and hose-clamped it hard onto a cylindrical chunk of metal with some silicone to get a good shape for a good seal to the reservoir.

At the bottom, sitting on the ground with a long rubber tube is another mayonnaise jar - identical to the top and half full. Connect the slave bleed nipple to the long brass tube with the long rubber tubing. You can see it bubble out air from below the fluid surface.

Raise car rear, connect up as above, open slave bleed - apply light air pressure with air gun pulses (don't blow up the plastic mayonnaise jars), wait for bubbles to stop at bottom. Pump pedal a few times while bleeding (there are two halves in the master and you want both connected.

If you want extra certainty (I always do), connect the air to the bottom and blow upwards. You can forward bleed or reverse bleed easily when set up this way. Watch fluid levels so the long brass tubes are always submerged.

I just got totally tired of fighting this. Now it works perfectly and easily. Plus it was cheap. I stick the bottles and hoses in a big greasy plastic Ziploc and it's ready to go for next time.

Good luck.

BTW, make sure you have the pedal set with the tiny clearance specced in the manual. If the pedal is pushing on the rod to the master, the master won't refill and pedal will eventually refuse to return full up.

[AKA_951]

That's a really good idea. I think I might try that. Another concept is how much to raise the front or rear of the car. Ideally, you want both to point up. The master is already pointing up and the slave is close to neutral. Maybe raising the rear just enough to have them both point up is ideal. Then I can't get under the car.

I was also thinking my pedal, right now, could be under vacuum since the last time I closed the system, the pedal was in. I doubt that vacuum pressure could affect clutch spring force though. Who knows

[89-944NA]

I'd also be checking for leaks in the system, if you are bleeding the system, and it works for a few weeks and then "feels softer" it sounds more like a leak than not completely bled.

Climb under the dash and feel around the top of the carpet, it it's damp your clutch master is leaking, also look for signs of leakage on the clutch master its-self. Next, look at that rubber clutch hose, they develop leaks at the metal crimping collar, check both ends for signs of leakage. Another hose to check is the blue hose that connects the fluid reservoir to the clutch master, they get old and leak.

Then remove the clutch slave cylinder and check that it is not leaking.

If you need to replace the blue hose, DO NOT use fuel line, you need hose specifically designed for brake fluid. Brake fluid will cause fuel line to deteriorate from the inside out, and fail at the most inopportune time (not to mention contaminating your system).

Seriously, consider the power bleeder, you will make your job much easier when it comes time to flush and install new fluid in your braking and clutch system...this should be done every 2 years.

[AKA_951]

It's funny you say that. I replaced the master because I could see it dripping under the carpet. I will work on it tonight and see where I'm at. The front of the car is raised, so I have to keep the tank filled to the brim. Then I'll raise the rear and finish off the system. If this doesn't work, I'll take further action. I think I can muster up some parts from ace to make that mayonaise jar idea a tad sexier.

[aj951]

Seriously, consider the power bleeder, you will make your job much easier when it comes time to flush and install new fluid in your braking and clutch system...this should be done every 2 years.

++1^

Worth every penny and makes bleeding the breaks and clutch a 15 min job. It's also good for revealing leaks.

A.J.

[Turbo17]

Originally Posted by AKA_951

That's a really good idea. I think I might try that. Another concept is how much to raise the front or rear of the car. Ideally, you want both to point up. The master is already pointing up and the slave is close to neutral. Maybe raising the rear just enough to have them both point up is ideal. Then I can't get under the car.

I was also thinking my pedal, right now, could be under vacuum since the last time I closed the system, the pedal was in. I doubt that vacuum pressure could affect clutch spring force though. Who knows

I've had every component of the brake system open and disassembled on my bench. The slave cylinder has a nipple at the top rear and an inlet at the front. With the rear of the car elevated (or the slave cylinder dismounted and tilted back end up, you will get all air out if bleeding from the top down. Since the fluid wants to drain out from the master to the slave, you can push fluid up, which will clear bubbles from the tubing and push them into the master, then let gravity drain the fluid back and close the slave nipple. This clears the slave and tubing.

The master is trickier. The outlet is low at the front. There is a piston inside (with a spring in front to push it to the rear) that divides the master cylinder into multiple compartments. Air bubbles can get trapped around the piston. Finally, there's a hole at the top of the master that leads to the reservoir. The hole is connected in front of the piston (and from there to the slave) when the piston is full back (foot off pedal and pedal up). The system seals itself with the hole behind the piston as the pedal moves to the floor. When you lift off the pedal, the spring in the master slides the piston to the rear and eventually connects the front half to the hole letting in more fluid. If you forget to move the pedal when bleeding, you don't bleed the rear half. If you leave the pedal down, you tend to trap air around all this.

If someone tries to adjust the brakes at the pedal, and removes the clearance (so the pedal pushes on the rod all the time, the piston can't move far enough back to open the system to the fluid reservoir. As the clutch wears, it can't get the additional fluid it needs (unless the internal master cylinder seals leak) and you get problems - pedal won't come back up, etc.

In theory, it should be possible to pump out all the air with the pedal, if the rear of the car is up, and I have done this, but it just isn't reliable enough, at least not for me. The only thing that worked repeatedly for me was to bleed in both directions. I was able to do it with a large syringe (came with a master cylinder I bought for another car) and with an oiler (clean/new - the type that holds a cup of oil and pumps it out with a trigger), but the easiest method for me was what I described above. It let me see when air stopped bubbling out.

[AKA_951]

Is there a possibility, during bleeding, that air can get sucked in through the seal that the plunger goes into (also the one that leaks into your floorboard) due to a vacuum on the system when pulling the pedal back out, when the slave nipple is closed, and the piston has not made it back far enough for the reservoir relief?

What I am asking is, is the rear seal as effective under vacuum as it is positive pressure (normal operation)?

This thread is extremely helpful

[kdjones2000]

BY FAR the easiest way to bleed the clutch line if you don't have a power bleeder (Or Motive, or....) is to get things bled as well as you can with the nipple at the slave cylinder, and THEN BLEED THE SOFT LINE AT THE UPPER CONNECTION.

What happens is that there is air trapped in the relatively large diameter rubber hose, and pumping the clutch does not displace enough volume to move the air bubble. Just crack open the soft line at its upper connection when the clutch is depressed, and within a couple of strokes you will have it bled.





Good luck, Keith

[AKA_951]

Great!

That makes sense. The fluid can push bubbles down when it's in the hard line, but that rubber line is too large. I bet 95% of the air trapped in people's lines is at the top of the rubber hose. The other 5% is probably the master and slave cylinders. I will try this and let you know how it goes.

I think another way is to pump the pedal vigorously to form a frothy mix of air and fluid. Use that as a body to move air through the rubber hose. Then continue to move the froth out the slave nipple.

[Turbo17]

Originally Posted by kdjones2000

THEN BLEED THE SOFT LINE AT THE UPPER CONNECTION.

I'm sure this works for others, but after I crawled on top of my jacked up car and worked to get that connection loose and fitted paper towels around to catch the fluid, and then struggled in the slippery mess with my feet dangling in midair to get the wrench in position to close it up again, I still had air somewhere.

I'm confident that it's smart to bleed there if you can't apply pressure, but it was worth it for me to figure out how to apply pressure.