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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Lan.Jet

Nice work!

I have done this for a couple of years I also found that putting a heat shield or sock over the line helps a lot.
http://www.jegs.com/i/Thermo+Tec/893/18101/10002/-1

beerkat

Nicely done video. It helped reaffirms that what I am doing is right.

95jersey

I did not know that you could empty the resivouir completely. I thought (like doing a brake bleed job) you had to leave some fluid in the bottom of the resivouir so no air gets in the system. I guess that is not the case for the clutch?

EvilBoffin

In case you're not familiar with Ranger, he is THE most respected expert regarding proper launching techniques and clutch care of C5/C6 Vettes. Just take a look his drag racing videos to see how it's done. Even with his incredibly aggressive launches (and incredibly fast 1/4 mile times in a STOCK C6Z06), he does not abuse his clutch.

The reason it's OK in this case is, you're NOT pumping or bleeding the system while the reservoir is empty. In fact, you never actually 'bleed' the system elsewhere like you would with brakes. You suck out all the contaminated liquid from the reservoir first, THEN immediately fill it with fresh fluid, THEN pump the new fluid into the system, pulling more bad fluid back up into the reservoir, THEN repeat until it's all clear. Done correctly, you won't introduce air into the system.

Keep in mind that a REAL clutch bleed is a major pain in the a$$, due to the horrible location of the stock bleed valve. Ranger's alternative "Turkey Baster" method can only introduce a reservoir's-worth of fluid into the lines at a time, so it takes a while. But the end result is just as effective as a full flush, and you don't need to break your back or buy special tools to accomplish it.

What the video doesn't show is that you may be repeating the whole process as much as 6-8 times before all the contamination is fully flushed out (depending on how filthy your current fluid is). It may seem like a tedious hassle to go through this every few months, but your clutch will last much longer and it's action will feel noticeably better, too.

burners

Good information, thanks for the tips. I had no idea that the fluid circulates.

EvilBoffin

Yeah, on top of it collecting that nasty clutch dust and moisture, the fluid lines actually travel through the bellhousing itself, exposing the fluid to all that heat, too.

So, yet another reason to flush your fluid on a very regular basis...

wallyman424

I remember ranger from when I had a street c5z and he was poppin off 11's with stock tires.

damn drag racers.

63Corvette

Welcome back Ranger, and Thaks for posting your very informative video. We your fellow Forum members appreciate the effort you have put into helping us.
Thanks,

Ranger

Appreciate the generous words sent my way.

I've been off-the-grid much of the past year. Hoping that lessens this year. Best to all.

Ranger

Everett Ogilvie

Nice to see you back here John, we have missed you. Nice job, and stay around!

Everett

Exotica

Ranger, thanks for taking the time to put this video together. I've been reading your posts for years, even before I bought my Corvette. Great input for all of us.

Joy of 6

Ranger,

Thanks for the detailled info. and the affirmation.

However, I have never seen an explanation as to whey the pedal sticks. Can you elaborate as to why the dirty fluid causes this problem?

thanks,

Ed

Ranger

Hi Ed,

My belief is there are two main causes

(1) water in the clutch fluid creates vapor lock in the hydraulic fluid under high operating temperatures of aggressive driving. Water is clear and give no visual tell of its presence. It enters the fluid during normal operation due to expansion-contraction of heat-cool cycles. The master cylinder has an emergency vent at the diaphragm/cap to relieve over-pressure. Humidity from the air enters there. Water content is kept in check by changing the fluid periodically.

(2) Clutch dust infused into the fluid is a more serious problem because it progressively nicks, mars and abrades the seals, creating trouble spots that lead to failure. The visual tell is murkiness cause by particles of elemental copper and iron and others that turn the fluid progressively black. The clumps of crud that tend to gather in the reservoir when the car is parked for awhile are clutch dust. Frequent fluid changes to minimize murkiness is the best way to protect the seals in the hydraulics.

Both those root causes have the effect of causing the clutch hydraulics to operate erratically and fail to return the rod in the master to its proper resting position. And, of course, air in the hydraulics causes erratic behavior also, such as changes to the engagement point.

That's an overview, based on my experience and observations.

Ranger

CertInsaneC5

Thanks for the post. Just checked mine and it is black!

Question: You showed in your video both DOT4 brake fluid and DOT4 brake and clutch fluid. Can I use either? Or is there something I missed?

Also, my diaphram is/was completely extended and didn't look anything like the one you showed in the vid. I have a 99' FRC BTW. Is this normal for that year car?

TIA.

Ranger

Hydraulic clutches use brake fluid. The label on the GM-brand can is for customer reassurance. Any good brand DOT4 fluid should work fine. Would stay away from Valvoline, which leeches to black almost instantly. If you use ATE Super Blue in your brakes, opt for ATE TPY200 (AMBER) for the clutch. Easier to detect a color change.

Remembering my C5Zs, the diaphragm will collapse into a stowed position. The max fill line is inside the reservoir and can be felt with a finger. I kept my clutch fluid somewhat below the max line.

Ranger

CertInsaneC5

Thanks man!

So....sounds like I need a new diaphragm as well. Adds more to shopping list.

Again Thanks for the help.

Ranger

Hi CertInsaneC5.

I erred on the position of the C5 diaphragm. Corrected my earlier post (see bold). Your diaphragm sounds fine.

Sorry for the inconvenience. Off to dinner.

Ranger

sothpaw2

Use a good high temp fluid like Motul 600. Even ATE is not that great if your seals are going and the fluid is getting heated up.

waddisme

Do you have any thoughts on the Tick MC which is supposed to cure these issues? Here is the thread:

http://www.ls1tech.com/forums/manual...its-299-a.html

I followed your recommendations since I got my WS6 4 yrs ago and have had no issues. I did put a new Spec 3+ clutch in my Vette and now the engagment point is so close to the floor, that I am constantly banging the gears when road racing. However, I am doing the Zmax 1/4 mi in Charlotte the first week of March. Thoughts?