Take Care of Your Clutch--How to Prevent or Cure Pedal Issues
02-18-2009, 11:47 AM
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Take Care of Your Clutch--How to Prevent or Cure Pedal Issues Click here 7-minute video in true wide-screen and high-definition versions
[Note: For HD, depending on your network connection speed, you may need to press the pause button to let the video preload part way, before you start watching. But the image quality makes it worth the wait.]
Clutch pedal issues have bedeviled Corvette (and other fast car) 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
----------------------------------------
How the Clutch Hydraulics Work
----------------------------------------
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.
Hope that helps.
---------------------------------------
How Clutch Dust Enter the Fluid
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 is getting into the fluid. The question is how. We believe the answer to that is in points 1-5 above.
---------------------------------------------------------
Minimizing Water Infiltration to the Clutch Fluid
Update February 23, 2009
---------------------------------------------------------
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.
--------------------------------
Details on Remote Bleeder
--------------------------------
Ranger
[Note: For HD, depending on your network connection speed, you may need to press the pause button to let the video preload part way, before you start watching. But the image quality makes it worth the wait.]
Clutch pedal issues have bedeviled Corvette (and other fast car) 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
----------------------------------------
How the Clutch Hydraulics Work
----------------------------------------
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.
Hope that helps.
---------------------------------------
How Clutch Dust Enter the Fluid
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 is getting into the fluid. The question is how. We believe the answer to that is in points 1-5 above.
---------------------------------------------------------
Minimizing Water Infiltration to the Clutch Fluid
Update February 23, 2009
---------------------------------------------------------
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.
--------------------------------
Details on Remote Bleeder
--------------------------------
Ranger
Last edited by Ranger; 03-08-2009 at 09:00 AM.
03-07-2009, 11:23 PM
#4
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As shown in the video, keep the fluid clear and clean. How frequently you will need to change it to keep it clean depends on how aggressively you drive. It's the clutch dust that makes the fluid black and kills the hydraulics.
May take 10-20 swaps over a week or so to get it clean initially.
Good luck with your car.
Ranger
03-08-2009, 12:04 AM
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I've used the two fluids shown in the video through 670 passes at the drag strip in three different Z06s. Prestone DOT4 is the cheaper of the two.
As shown in the video, keep the fluid clear and clean. How frequently you will need to change it to keep it clean depends on how aggressively you drive. It's the clutch dust that makes the fluid black and kills the hydraulics.
May take 10-20 swaps over a week or so to get it clean initially.
Good luck with your car.
Ranger
As shown in the video, keep the fluid clear and clean. How frequently you will need to change it to keep it clean depends on how aggressively you drive. It's the clutch dust that makes the fluid black and kills the hydraulics.
May take 10-20 swaps over a week or so to get it clean initially.
Good luck with your car.
Ranger
I've tried so many times since I've had my 6spd car to bleed the clutch using your method. It has never turned out right when I do it. I'd have my wife get in the car push the clutch down, I crack the bleeder quickly SEVERAL times, and by the time I'm finished new fluid would be coming out. Problem is it NEVER got bled correctly. NEVER! Everytime I'd end up having to take it to the dealership and they'd rape my pockets saying its a leaking slave!
Also slaves seem to have the shortest life out of all parts of my car including tires!
What's up?
03-08-2009, 07:09 AM
#6
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Ranger,
I've tried so many times since I've had my 6spd car to bleed the clutch using your method. It has never turned out right when I do it. I'd have my wife get in the car push the clutch down, I crack the bleeder quickly SEVERAL times, and by the time I'm finished new fluid would be coming out. Problem is it NEVER got bled correctly. NEVER! Everytime I'd end up having to take it to the dealership and they'd rape my pockets saying its a leaking slave!
Also slaves seem to have the shortest life out of all parts of my car including tires!
What's up?
I've tried so many times since I've had my 6spd car to bleed the clutch using your method. It has never turned out right when I do it. I'd have my wife get in the car push the clutch down, I crack the bleeder quickly SEVERAL times, and by the time I'm finished new fluid would be coming out. Problem is it NEVER got bled correctly. NEVER! Everytime I'd end up having to take it to the dealership and they'd rape my pockets saying its a leaking slave!
Also slaves seem to have the shortest life out of all parts of my car including tires!
What's up?
I have a remote bleeder on my cars but don't use it. Fluid swapping via the reservoir is easier and, unlike standard bleeding from below, never allows air into the hydraulics.
If clutch dust has accumulated in your hydraulics and turned the fluid black, it takes persistence to clean it out.
If it's been black for thousands of miles of aggressive driving, the clutch dust may have compromised the seals in the hydraulics such that clean fluid won't do the trick. But it's worth trying because it may work and it's cheap.
The real point is always keep the fluid clean and your clutch pedal will remain normal.
Ranger
Last edited by Ranger; 03-08-2009 at 04:25 PM.
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03-08-2009, 02:51 PM
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I've used the same one for eight years. MixMizer is widely available, including Walmart where it is usually on a pegboard near the gas cans in automotive. Costs about $3.00. Nearby is Prestone DOT4 for about $2.65 for a 12-ounce can.
Ranger
Ranger
Last edited by Ranger; 03-08-2009 at 04:26 PM.
