Ranger

I've found that a clutch change from (stock to stock), with fresh master and slave, will often put air in the hydraulics. That has the effect of putting the engagement point close to the floor. On mine I've corrected the problem by pumping the pedal a lot and driving the car. The diaphragm in the reservoir progressively gets compressed as the air works its way to the highest point in the hydraulics.

If that doesn't work for you...

The Tick adjustable master looks interesting. But haven't seen reviews of it by Corvette owners. I'd want to understand better the differences between the F-body and C5 versions. Might want to visit their shop, if you're close enough, and check into their ability to install what they sell.

Ranger

Rob Burgoon

Ranger, just to be 100% clear, you're saying that the clutch fluid circulates? As you pump the pedal, a fluid molecule marches down from the master to the slave cylinder, past the bleeder and then returns to the reservoir? There is a circular path here that traverses most of the system?

Ranger

Hi Rob.

It’s always a good idea to go to the source document for a definitive description of the operation of the clutch hydraulics. In this case the Corvette Service Manual 2006, Volume 3, page 7-360, and I quote:

The clutch hydraulic system consists of a master cylinder and an actuator cylinder.

When pressure is applied to the clutch pedal (pedal depressed), the pushrod contacts the plunger and pushes it down the bore of the master cylinder.

In the first 0.8 mm (0.031 in) of movement, the recuperation seal closes the port to the fluid reservoir tank, and as the plunger continues to move down the bore of the cylinder, the fluid is forced through the outlet line to the actuator cylinder mounted to the driveline support assembly.

As fluid is pushed down the pipe from the master cylinder, this in turn forces the piston in the actuator cylinder outward.

As the actuator cylinder moves forward, it forces the release bearing to disengage the clutch pressure plate from the clutch disc.

On the return stroke (pedal released), the plunger moves back as a result of the return pressure of the clutch.

Fluid returns to the master cylinder and the final movement of the plunger opens the port to the fluid reservoir, allowing an unrestricted flow between system and reservoir….

There you have if from the source.

Summary: Clutch fluid circulates between the master and actuator (slave).

Note: The volume of fluid in the entire system is a very few ounces. One ounce is in the master cylinder reservoir until diminished as you depress the pedal and create the flow described above.

Hope that helps.

Ranger

Rob Burgoon

Ranger, that is huge. I had blown off your process before since I was thinking "no circulation, crud isn't going anywhere".

Thanks for clearing that up! I'll certainly give it go.

Ranger

^^^ Happy to help Rob.

Ranger

davidfarmer

While I totally agree that regular "fluid exchanges", and occasional bleeds, are a great idea.......

How do you think clutch dust gets into the fluid.....yet fluid does not leak out???? I think it unlikely that a solid partical can penetrate through the braded line and/or the throw-out bearing and NOT allow fluid to leak out when the pedel is compressed.

I've seen things during brake bleeds as well, that look like solid particles.....but I think it likely is a byproduct of the fluid ageing/cooking process.

I personally never had any clutch problems with any of my C5/C6 street/race car until the C6Z06. Pedal just stoped coming up consistently. The procedure above didn't work, so I took the "helper" spring out, and it's been fine since.

Ranger

Clutch dust, is confirmed in the fluid. (See the lab report). And it is the elemental form of copper and iron (same at on the clutch disc). Those are only found in ionic form in degenerated brake fluid where they are sourced to a breakdown in the brazing compound of the metal lines.

The clutch dust must be getting past a seal, probably the main seal on the actuator; I suspect it is being squeegeed in during the seal's travel on the dirty shaft.

The image of floating particles in the clutch fluid sample involves fluid that had been in that vehicle's clutch hydraulics for only a few hours that included aggressive launches and shifts. That was sample #1 in the report. Those particles are confirmed as clutch dust.

I suspect no one has ever tested the fluid for clutch dust until now. And now that it seems it is clutch dust that is wasting the seals in the hydraulics, perhaps GM will look into the exact path and fix it.

There is a green bellows-type shield that covers the main shaft in the actuator. On the sample #1 car, there was a significant amount of dust under the shield. Gotta note that the air speed in the bellhousing is above 50 mph at high-rpm. Fine dust blown at 50 has a tendency to get into places you don't want it.

Just a thought.

Ranger

Axelrod

Duct tape

Ranger

I've edited the following into Post #1 on the thread....

Update February 17, 2009

Today I spent time at the workbench with two Chevy master technicians (one who’s worked on Corvettes since the C3 was first released). We examined the operation of the Corvette clutch actuator and concluded following:

1. The bell housing is fouled with blown clutch dust during aggressive driving.
2. Clutch dust is penetrating the accordion shield on the actuator main shaft. That is obvious from visual inspection.
3. The piston slides along the shaft sealed by an O-ring. The shaft has a film of lubricant or clutch fluid on it. During aggressive driving, this film gets coated on each stroke with a fine layer of blow clutch dust. That is obvious from visual inspection.
4. The O-ring slides along the shaft and squeegees some of the clutch dust down the shaft where it contacts the clutch fluid and is infused.
5. The conclusions were unanimous and seemed obvious from a physical exam of the surfaces involved.

Plus, keep in mind that it is confirmed that clutch dust in getting into the fluid. The question is how. We believe the answer to that is in points 1-5 above.

Ranger

John Shiels

Thanks Ranger except I am embarrassed as it is the most neglected part on my car.:o:o:o:o:o

hapnermw

Ranger,

Thanks for the work you have put into this for the community.

I've been following your turkey baster process every month or so for the last two years but never pumped the clutch after. The fluid is always discolored and the reservoir always has some black residue.

After viewing your clip, I was expecting to find that pumping the clutch brought additional contamination up from the clutch; however, after pumping, the fluid in the reservoir was still clear.

This seems to indicate that, for some reason, the clutch dust is accumulating first in the reservoir.

kentz06

Glad to see you back!

Will we get to see you at TA09?

Dean

Ranger

Hi Kent.

If I'm not off-the-grid, I plan to be there. Won't know for sure until late-April. Would hate to miss the splendid learning environment for those curve-things and the opportunity to hang again with you, Everett, Mike, Frank, Jim and the other racers.

All the best.

Ranger

burners

Very good information, thanks! I just performed this maintenance on my GTO because of this thread. The fluid was jet black. The car has 55,000 miles on it and the clutch has never been touched. I did just what was recommended, removed the fluid probably 5 times and it was finally clean but I just took it for a test drive and the fluid is pretty dark again so I'm off to do it some more.

Lawdogg

I have been skeptical of reservoir fluid changes since Ranger first posted about them a long time ago. Even though skeptical, I have always removed the old fluid and filled with new every week just in case he was right. My fluid is always clear due to these frequent changes and I have never had pedal issues. The car is tracked now and then both 1/4 mile and road courses.

Having an over-centering spring, a line restriction, and a throwout bearing prone to having its plastic housing scored always seemed to me to be the likely cause of the soft or dead pedal. In any event, great research and work by Ranger.

Ranger

Clutch Bleed Procedure Using Remote Bleeder and a Helper

I have a remote bleeder on my car but don't use. I find the reservoir method is easier for me. But for those who wish to bleed via a remote bleeder, here is the way. Be very precise in the sequencing. If you're not, you will introduce air into the hydraulics.


Start by placing a section of clear tubing over the remote bleed valve nipple and running the tube to a clear plastic bottle, so that the expelled fluid can be seen. Light the tubing and bottle appropriately. Then:

1. Replace fluid in the reservoir with fresh DOT4. Clean diaphragm and replace cap.

2. Helper pumps the clutch pedal five times slowly full-top to full-bottom to full-top. Helper then takes foot off pedal.

3. You open the remote bleed valve.

4. Helper slowly presses the clutch pedal to the floor and holds it there.

5. You re-tighten the bleed valve.

6. Helper releases the clutch pedal.

7. You refill the reservoir to the fill-line and replace the cap.

8. Repeat steps until the expelled clutch fluid remains clear and shows no air bubbles.

9. Final step is to correct the fluid level in the reservoir.

10. Go for an easy drive without launch or high-rpm shifts. Check clutch engagement point and shift smoothness.

11. Repeat at lease one more time as required to disgorge trapped air.

Ranger

cj68

I have been using Ranger's procedure for a few years now and have noticed one thing. When I use Valvoline brake fluid, the resevoir fluid stays fairly clean. When I tried ATE gold, the fluid turned black very quickly, almost as if it was reacting with the rubber seals.

This is contrary to what Ranger mentioned in his early post.

Thoughts?

VetteDrmr

CJ68,

Actually, I've always used Valvoline Synpower in my clutch reservoir and noticed that the clutch fluid has stayed pretty clean. I wonder if there's something subtle going chemically?

In any case, I think Ranger's approach&plan work, and when things work, theory takes much of a back seat.

Have a good one,
Mike

cj68

Same here... I am glad that someone else is expereincing the same thing. I am going to stick with the Valvoline and continue to do Ranger's clutch maintenance procedure regularly. Also, I have not had any clutch problems... pilot bearing, yes, but not the clutch.

Thanks,

cj