Ranger

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Clutch pedal issues have bedeviled Corvette owners since the advent of the C5. I got on the case after buying my first Z06 in August 2000 and pedal woes bit my new car. Since then, I’ve learned a lot about the maintenance a clutch needs to keep performing normally under aggressive driving. And I’ve shared those insights in many threads, emails, private messages and phone calls over the years.

To get the word out more effectively, I’ve distilled that knowledge into a seven-minute video that lays out the symptoms and root cause, and demonstrate a protocol for prevention and cure of clutch pedal issues.

I particularly want to thank George Westby, Director of the Advanced Process Laboratory of Unovis Solutions and his lead engineer Martin Anselm. They collaborated in the analysis of clutch fluid and clutch dust samples, which I sent them from 2006 Z06s.

Click here to download a copy of the Unovis lab report

That report forms an important basis for concluding that clutch dust is infusing the clutch fluid of aggressively driven cars. And it is clutch dust that, if allowed to accumulate, constitutes an abrasive that damages integrity of seals in the hydraulics.

For clarity sake, driven “aggressively” means cars that are launched or see high-rpm up-shifts or down-shifts. And consequential clutch problems affect many brands of car besides GM and motorcycles too.

The good news is that we have figured out the root cause. That means the preventative maintenance (frequent swaps of the fluid via the master cylinder reservoir) definitely works. It also explains why, if the seals are already damaged by clutch dust, no amount of clean fluid will heal them. The crucial element is prevention, never allowing the clutch dust to accumulate in the fluid. The tell of its presence is murkiness or cloudiness. So don’t allow the fluid to stay murky.

I think water entering the fluid via heat-and-cool cycles plays a roll in clutch pedal issues. So frequent changes of the clutch fluid ought to be part of routine maintenance for owners who don’t do aggressive launch or shifts. Suspect there are a few owners like that around.

Hope the video helps more owners avoid the trouble and expense of clutch pedal issues…and helps GM further reduce warranty claims for clutch issues easily avoided by preventative maintenance. The routine I personally follow costs about $20 and two hours of my time per year. That’s a small investment with a big return in reliability and driving pleasure.

Best to all,

Ranger

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How the Clutch Hydraulics Work
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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….

Close Quote. 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.

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How Clutch Dust Enter the Fluid
Update February 17, 2009
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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 is getting into the fluid. The question is how. We believe the answer to that is in points 1-5 above.

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Minimizing Water Infiltration to the Clutch Fluid
Update February 23, 2009
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I've been following the protocol for eight years now and never had shift-related pedal issues. That's includes a lot of burnouts, launches, and red-line shifts. So what I'm doing is definitely effective.

Brake fluid is indeed hygroscopic. By my approach the cap is off the reservoir for very brief periods and, while that occurs, each time you are swapping about 35-50 percent of the used fluid with new. Do that one-to-three times and the impact of water absorption from the atmosphere is essentially nil. In fact the more times you make the swap in succession, the less the impact of transitory water infusion.

The industry standard for "wet" boiling point is the fluid containing 3% water. That's amount of water infusion is not going to happen in fluid that's kept clear and fresh via the reservoir. I suppose water infusion can be an issue if you remove the cap from the reservoir outdoors on a very humid day (or in the rain) and then take a lunch break. But few of us would do that. And a couple flushes by the protocol and the water is gone anyway.

Another aspect of risk is using brake/clutch fluid from a can that's been open for months or left with the cap off for an extended period. That's ill-advised. But I routinely keep a can going for 30-60 days by....
(1) cutting a slot in the membrane at the neck vice removing the entire seal
(2) replacing the cap when not pouring from it
(3) keeping the can in double layer of double-seal zip-lock bags between uses

Those steps minimize moisture infiltration to a can that's been opened.

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Details on Remote Bleeder
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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

VGLNTE1

wow.....back from the dead. WTF have you been?!

lucky131969

Thanks for posting the information, your contributions are well noted on the forum, and your techniques speak volumes in your own 1/4 mile times. After reading the report, I have some questions:

1) Where was the sample fluid extracted from? Master cylinder? Bled from the slave?

2) Where was the clutch dust sample taken from? Directly taken from the clutch friction disc, or was this material sampled from the the inspection cover area? If it was taken from the inspection area, how can wear from the flywheel and the friction disc be differentiated.

3) Samples #1&2 are identified as "used and new fluid" Does this mean there were unused samples of Prestone and GM fluid tested? Typically these would be labeled as control 1&2 respectively. The SEM/EDXA was shown for the lab filter why nothing for the new(unused) fluid?

4) While the conclusion states the elements in samples 1&2 are similar to that of the clutch dust, the results are inconclusive. That being said, how does clutch dust infiltrate a sealed/pressurized system if no leaks exist?


High levels of copper and iron have been attributed to the degradation of brake fluid in braking systems as well (plenty of info on this subject). The levels of copper and iron found in brake fluid are attributed to corrosion over time.

XtremeVette

Wow! I second this.....Where the hell ya been ranger...Still waiting on that Driving DVD to be released...been a couple years now! I know, I know your a very busy guy....Any chance it will still be released? Just curious....anyways....good to hear your still a part of the forum and are around. I was thinking you left and jumped into imports or something

Ranger

Responses keyed to your questions.

1. The used clutch fluid samples were collected from the master cylinder reservoir AFTER the hydraulics had been given a good workout to agitate the fluid and bring precipitated particulate into suspension. Both sample were from stock 2006 Z06s. Two different cars.

2. The clutch dust was collected from the rotating clutch disc on a disassembled LS7 clutch which was pulled out specifically for this test. It was this car that also contributed one of the used clutch fluid samples.

3. Sample #1 was Prestone DOT4 based. There were two containers. One with used fluid, one with new fluid. Sample #2 was GM Super DOT4 based. There were two containers. One with used fluid, one with new fluid. I label the new samples as "new" rather than "control." Page 1 of the Unovis report shows the container for each sample and the handwriting on the lids is mine.

4. What was found in the used clutch fluid samples and the raw clutch dust was "elemental" copper. If you inspect an LS7 clutch disc face you will plainly see strands of copper woven into the friction material to help dissipate heat. In contrast the the form of copper found in degraded brake fluid is "ionic" because it originates from the alloys used in brazing the coiled metal brake lines. Element copper is nowhere found in the hydraulics. But it is found on the clutch friction surfaces. That is seen as conclusive.

Regarding the means of clutch dust infiltration into a "closed" hydraulic system....

(a) The first thing to recognize is the bell-housing is seriously fouled with clutch dust during aggressive driving. And those dust particles are moving at significant speed.

(b) The clutch dust particles are pelting the actuator seal and getting under the shield (the bellows which is green when new), and also hammering the mating surface of the connector that joins the master to the slave. I suspect that movement of the seals is having the effect of squeegeeing dust. Because the dust particle size may be smaller than the fluid molecules, the passage occurs in but not out.

Ranger

DRR

Well done Ranger!

Bravo for the clutch dust contamination discovery.

As with any contamination issue, dilution is the solution.

I wonder if the method Ranger uses, removing spent fluid via the master cyl, is more, less or equally effective to bleeding via an aftermarket bleeder?

I use a Mity Vac to bleed via my remote bleeder. I always begin by pumping the pedal to agitate the fluid, then emptying, cleaning, and refilling the master reservoir prior to bleeding. I try to do this every month.

Consider this question: Is the method I use better, worse, or the same in effect?

Doug

Ranger

Hi Doug.

If your method is working, e.g. keeping up with or ahead of the onset of murkiness brought on by clutch dust, then there is no reason to change.

You are wise to agitate the fluid strongly before beginning the remote bleed. Absent that, any crud would likely remain settled at the bottom of the actuator (slave). That's because both the bleeder connection and the master cylinder connection are near the highest point in the slave and directly adjacent to one another.

Ranger

lucky131969

Ranger,
Thanks for the reply. So the belief is that clutch dust is infiltrating the seal at the slave, and somehow migrating up to the master cylinder? I believe the copper/iron contamination is contributing to the demise of the clutch fluid for sure. The only way to be sure, would be to sample fluid from the slave and have it tested. I also think it would be interesting to have the fluid tested from the brake master cylinder. Like I said, high levels of copper/iron are found in braking systems, and directly attributed to the degradation of the fluid. Same fluid.....no clutch dust involved.

Again, thanks for posting. With some more testing, it will lead to interesting conclusion.

hfddirty30

THANK YOU RANGER!!!!!!
This makes me feel a lot better after buying a used '04 with a 6 speed.Found clutch fluid dirty after purchase,did the procedure and fluid cleared up on second filling,now do the procedure once a month and everything is working fine.Thanks again!!!! ED

Ranger

Sample #1 was fresh fluid with six drag strip passes on it. It had been in the hydraulics for just a few hours. The iron and elemental copper in the that fluid entered via infused clutch dust.

If you are interested in more testing, you'll need to be designing and conducting the tests yourself. I've gone as far on this as I think necessary.

My aggressive driving friends keep their clutch fluid clear through frequent reservoir changes. They remain inoculated to clutch issues.

Meanwhile, owners driving with black clutch-dust laden clutch fluid continue to have pedal issues rooted in compromised hydraulic seals.

One last thing, the action of pumping the clutch pedal causes flow within the clutch hydraulics, commingling fluid between the master cylinder and actuator (slave). So in well agitated fluid, say after 30 pedal pumps, the fluid would be generally uniform throughout the hydraulics. Said another way, there is no benefit to testing samples taken from the actuator.

Ranger

Toque

Thanks Ranger !

I have been doing your procedure for a couple years now and my fluid is always clear now. I just keep an eye on it and have some new fluid handy when it starts to darken....

Thanks !
Toque

lucky131969

I guess we'll never know..

Thanks again for sharing.

monza_man

Great post!

DRR

Quote: I guess we'll never know..

Well...
Someone with a remote bleeder could pull a sample directly from the actuator and have the same test run to compare.

lucky, do you suspect the fluid will have a higher concentration of contamination at the actuator versus at the master, even after agitation?

Doug

chevy406

Good information here for me to implement with my clutch replacement this weekend. I have a remote bleeder, and will be putting it to use! Thanks Ranger.

mnpoika

Thanks to all who contributed to this excellent post. I'm reminded of my visit to a drag srip after many years of absence. During the SEMA Show in Las Vegas this past November, our tour attended the NHRA Nationals, where I was marveling at the exotic machinery in the pits. Asking about the parts unfamiliar to me, I learned that the dragsters are required to have their bell housings vented into a filter to keep clutch dust from being discharged into the atmosphere or onto the track. Evidentally the wear and discharge of clutch material is greater than intuition would suggest.

lucky131969

Ya know, I'm not going to push it, because Ranger has made a serious contribution to this forum. Hell, his suggestions helped me immensely launching my C5 after the vortech install. I had to learn how to drive the car all over again.
I only know, based on my professional experience (and data presented), that more testing would be required for me to draw a conclusion.

In any case, Ranger's suggestions are solid, and changing the fluid on a regular basis should alleviate a number of issues for a great number of owners.

DRR

lucky,

Ha. I meant you take the sample and send it to the same place as the others for results.

IrishMac

Excellent!

lucky131969

Actually, Trace Labs is about 4 miles from my house, and I do have a friend who works there. I'll see what I can do.