I'm not bashing, just stating the physical imposibility of your methodology. I'm not the only one who doubts this works but yet you choose to only challenge me.
Obviously the system is open to the atmosphere at the reservoir, duh! As stated in a previous post, I did try this, it did not work. Pressure below atmospheric pressure is reffered to as "being under a vacuum".

 

First off the posting of a process that works to remove entrapped air from the clutch hydraulic system is for the benefit of those that are faced with this task. It gives them one more option that they may not have been aware of. It’s is called being helpful, what I believe is the whole purpose of these forums. What is the focus of your post?

You have made many comments in your posting that are not true yet you feel “challenged” when questioned about them. Example, Here you state that it is “hermetically sealed”. Do you understand what that means?

So which is it? Is it hermetically sealed or not?

One more question for you, and I’m asking this with the hopes of giving you a key as to why this process works and to help focus your effort on understanding why it does and get off of, in your words, “physical impossibility”. If you truly understand physics then this should be no challenge to you at all.

If there is an air bubble in the slave cylinder at atmospheric pressure, and I decrease the pressure using a hand vacuum pump, what changes might I expect in the size of the air bubble?

 

PM'D you

 

If accumulated clutch dust has destroyed the integrity of the seals in your clutch hydraulics, then no amount of clean fluid will heal them.

So clean the fluid thoroughly to the point that it remains clean after a drive. If pedal issues remain, the next step is replacing just the master cylinder using the most current part for your VIN. That will usually fix it.

From that point on, keep the fluid clean through frequent swaps.

If a new master doesn't restore a normal clutch pedal, then the fix gets more expensive and requires dropping the drive-train.

Ranger

 

Eric, I understand the physics very well, more than you can ever imagine. I tried this experiment against my better judgement when I was having problems with my clutch based on the commentary about it in the forum, it did not work!
Continue recommending this procedure to your hearts content, I will no longer participate in vacuum bleeding discussions.

 

Well that's a real shame...just when I thought we were getting somewhere.

 

update:

replaced the clutch master cyl and everything is fine and dandy.

I've read on f-body website about doing this might vac bleed too, it apparently works for some.

 

Glad the new master did the trick.

Whatever method you choose, keep the fluid clean from here on out and protect the hydraulic seals from the ravages of clutch dust.

Ranger

 

Glad to hear you got it fixed! Any problems getting the new one in?


on keeping it clean.

 

I had to remove the clutch master once because i ran the hydraulic line OVER the steering shaft. Oops. Besides that it went pretty smoothly. I like the simple push and turn for attaching the master to the firewall. The f-body involved nuts and bolts and was a pain for one person to do.

The only other mishap was when, while all happy that i discovered the clutch pedal to be feeling better i hopped out of the car and promptly slammed my fingers in the car door. A fifteen minute break and a bandaid later and i was finishing things up for the cars first ride in 2 weeks! rotfl.

Thanks for the input everyone. Ranger, i'll DEFINATELY be watching that clutch fluid. I flushed my filthy break system also. Gotta love that mighty vac.(well actually the cheaper version from harbor freight)

 

I know it's an old thread but I did a search before posting a question regarding bleeding the clutch hydraulics and this thread turned out to be very, very useful. Huge thanks to Eric D. for his suggestion on how to bleed the system without doing so from the bleeder valve. Creating a vacuum at the fluid reservoir works perfectly. Excellent suggestion and method. There is no need to get under the car to remove all the air out of the clutch hydraulics. The bleeder valve remains closed you remain on your feet and the air is all evacuated away in minutes. This is an easy one person job now. Thanks!!

 

How do I do this?

 

Eric D...Da Mann! Thanxs! Your tip is spot on. Laws of physics still apply. Purchased a Mightyvac/Ag useage. Saved me time & $$.

 

Well, what the heck: with the pro/con on the closed-bleeder-valve, vacuum bleeding process, I just decided to set up an experiment with clear tubing and maybe learn something.

I set up a pretty simple rig using a Mighty-Vac and some clear tubing.
I formed the tubing in the general shape and length of of the clutch fluid lines on the C5. As we know, the line going down from the master dips down, then loops back up to enter the torque tube, then down to the slave. The line up from the master to the reservoir is virtually vertical.
So, we have some ups and downs in that line to contend with when we try to push air bubbles around.
Of course, the master cylinder plunger is retracted during this process, so the line is open from the slave all the way up to the reservoir.

I plugged the end of the tube (like closing the bleeder on the slave) and dumped fluid in the line, intentionally trapping a couple of air bubbles down near the slave end, and in the high loop in the line simulating the high section as the line exits the torque tube and dips down before moving upward to the master cylinder.
Then I hooked the Mighty Vac cup up to simulate the procedure of sealing off the top of the clutch reservoir with a stopper, in preparation of pulling vacuum thru the reservoir. I diddled around with it for awhile, shaking/tapping the line, pulling various vacuums from 10-20 inches, and watching the actions of the bubbles.

Observations:

1. With the "reservoir" open to the atmosphere, air bubbles moved fairly freely up the vertical tubing from the lowest point of the line below the master, on up to the reservoir. However, a small bubble or two adhered to the tubing and did not immediately move on up and out. A couple of taps on the tube or a little shaking moved them right out. (see below what effect the vacuum had on them).

2. With the reservoir open, the large bubble on the far end (slave) adhered for awhile, but with a slight tap or shake it moved on up to the high loop section (outside the torque tube). It of course would not move farther, since it would have to travel downward to do so.

3. When pulling vacuum on the line, the small bubbles adhering to the vertical walls of the tubing grew in size as expected, and broke loose and moved on upward and out into the reservoir, very similar to the action when the line was tapped or slightly shaken.

4. With a vacuum, the large bubble down on the end (slave) grew in size significantly, and quickly moved up and joined the other bubble in the high spot in the line (simulating the portion outside the torque tube) This large bubble did not move toward the "exit" at all, but expanded in both directions evenly, both down and up the line in the loop. However, as the bubble grew, a portion of it expanded to a horizontal section of the ascending tube, and was pulled on up and out.
The majority of the bubble remained in the loop, moving neither up or down as vacuum was applied.

Conclusion: everything happened as expected.

1. Applying vacuum to a closed tube containing a liquid with entrapped bubbles does nothing to move the bubbles around rather than increasing the size of the bubbles, which in some cases helps smaller bubbles break free from the vertical tubing walls and escape upward.
Also, small bubbles will grow and possibly combine, to move up and out easier.
A very large bubble in a tubing loop may expand to the point that a portion of the bubble is expanded to a horizontal or slightly vertical section of the tubing, and is released to float upward and out. But the remainder of the bubble will not follow.

2. With the exception of the above, the vacuum will not move the bubbles toward the source of the vacuum at all.

3. If there are very small, entrained bubbles in the fluid, it seems unlikely that a vacuum of this magnitude, duration, temperature would have much impact in coalescing these to sufficient size to be removed.

4. tapping or shaking the line would seem to have as much effect on moving the air bubbles out as applying a vacuum to a closed system.
Working the clutch pedal would appear to have even more effect, as it should actually move the fluid and the bubbles up and down the line, breaking some free to move up and out.

So, where do the reported successes, and the reported observed bubbles erupting up into the reservoir come from?

- Perhaps improvement comes from the effect of the bubbles increasing greatly in size as the vacuum is increased. This allows some to escape and move out, but should never free all of those trapped in a high loop of the line.

- Perhaps the act of sucking the rubber slave "piston" back in the bore helps move the fluid/bubble mix slightly towards the reservoir, releasing some more of the bubbles.

- Perhaps most GM vehicles don't have that high loop in the clutch line, thus giving the vacuum method a much better chance of drawing out the bubbles as they increase in zize due to the vacuum.

So, based on my little test, and a general knowledge of fluid dynamics, I conclude that the vacuum bleeding process may help a C5 system a bit, but will never remove all the air trapped in the high loop outside the torque tube; and that tapping/shaking the line, pumping the pedal, driving the car are just about as effective.

And a final thought: if we are getting wear on the slave piston/seal, and maybe clutch dust is intruding; if we apply a vacuum to the system, would it be possible for a small amount of air to slip by the slave piston seal and aggravate our bubble problem even more. Probably not, if the fluid is not leaking out under hundreds of PSI, but just another thing to consider with the vacuum technique.

Whew,
DG