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Discussion Starter #1
It's possible my Master Clutch Cylinder has a problem.

Symptoms: The clutch pedal loses pressure immediately after I floor the car and shift at high rpm, such as accelerating onto a highway. It occurs only when the rpm exceed 5,000. To rebuild the pressure, I need to pump the clutch three to six times and then it is perfect again. The pressure will remain that way for weeks with no change. But as I just mentioned, the first time I floor it and shift at high rpm, the clutch loses pressure.

At first I thought I had air in the system, but then I realized any air would affect pressure all the time. As mentioned, the pedal pressure feels great when driving normally. (I'm pretty sure that makes sense.) But here's another part of this conundrum. The system has no leaks and the fluid level in the reservoir never changes. In order for the closed system to lose pressure, wouldn't fluid have to escape for air to enter? If air enters, how does it get in? And of the course big question is why does this happen only (and abruptly) at high rpm? A clutch system is really simple, yet I'm not certain how to diagnose these symptoms.

Next, I checked online and can order a new master clutch cylinder for my car for about $86. (That's not the end of world.) To the best of my knowledge, Honda states labor to replace it is 1.5 to 2 hours. That's about $150 to $200 for labor. If I choose to do the work myself to save that $200, are there any tricks I should know in advance to get it right the first time? Or, is this one of those jobs that is worth paying to have it done?

Any opinions on my diagnosis or tricks on how to do the work would be much appreciated. Thanks in advance.
 

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It's possible my Master Clutch Cylinder has a problem.


Any opinions on my diagnosis or tricks on how to do the work would be much appreciated. Thanks in advance.

I sure hope that the dreaded slave cylinder is not returning to cause you grief.

best, ez....
 

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Discussion Starter #4
For those interested, the symptoms listed above were related to a loose bleeder valve. As many of you know, I removed the dampening valve from my slave cylinder. After reinstalling my slave cylinder and bleeding the clutch system, it seems I did not properly tighten the bleeder valve. (I thought I put plenty of torque on it, but apparently not.) Over time, it slowly loosened.

This weekend after pulling onto a local highway, I lost all pressure in the clutch system. The pedal hit the floor and would not come up. After pulling over, I popped the hood and noticed the rubber cover to the bleeder valve was missing and there was fluid around the slave cylinder. It was immediately obvious what happened. So I called my wife to come to my rescue with my tools and a bottle of brake fluid. I tightened the valve, refilled the reservoir, pumped the pedal to build pressure and drove home. Today I had a 10:00am appointment at my local Honda dealership. I had them bleed the clutch system and make sure the bleeder valve was properly tightened.

The tech confirmed the theory that the engine's high-rpm vibrations caused the bleeder valve to vibrate and loosen. Apparently the bleeder valve did not vibrate at low and mid rpm. During those few seconds that the high-rpm vibrations caused the bleeder valve to vibrate, it let in air which immediately caused the decrease in clutch pressure. Although the bleeder valve was technically loose, because it did not vibrate at low rpm, it remained tight enough to seal the system and permit me to pump the clutch pedal and rebuild the pressure in the system. Of course that lasted until the valve finally fully opened and released all the pressure.

Mystery solved......
 

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For those interested, the symptoms listed above were related to a loose bleeder valve. As many of you know, I removed the dampening valve from my slave cylinder. After reinstalling my slave cylinder and bleeding the clutch system, it seems I did not properly tighten the bleeder valve. (I thought I put plenty of torque on it, but apparently not.) Over time, it slowly loosened.

This weekend after pulling onto a local highway, I lost all pressure in the clutch system. The pedal hit the floor and would not come up. After pulling over, I popped the hood and noticed the rubber cover to the bleeder valve was missing and there was fluid around the slave cylinder. It was immediately obvious what happened. So I called my wife to come to my rescue with my tools and a bottle of brake fluid. I tightened the valve, refilled the reservoir, pumped the pedal to build pressure and drove home. Today I had a 10:00am appointment at my local Honda dealership. I had them bleed the clutch system and make sure the bleeder valve was properly tightened.

The tech confirmed the theory that the engine's high-rpm vibrations caused the bleeder valve to vibrate and loosen. Apparently the bleeder valve did not vibrate at low and mid rpm. During those few seconds that the high-rpm vibrations caused the bleeder valve to vibrate, it let in air which immediately caused the decrease in clutch pressure. Although the bleeder valve was technically loose, because it did not vibrate at low rpm, it remained tight enough to seal the system and permit me to pump the clutch pedal and rebuild the pressure in the system. Of course that lasted until the valve finally fully opened and released all the pressure.

Mystery solved......
Baldeagle,

I'm new to the forum, found it while google searching for master cylinder issues. I've got the exact symptoms you described on my 2004 Accord V6, clutch pedal gets soft and returns slow after a high-rev shift (5000 rpm and above). Sometimes it's so soft that it won't disengage the clutch again without a few good pumps. If I stay below 3000 rpm, no problems whatsoever. I can hold the pedal down in any position all day and it won't lose pressure or return slowly. I was having the same thoughts as you, "if there's a leak in my closed-hydraulic system, why is it only manifesting itself at high-rpm shifts??". I'm hoping my fix is as simple as yours too. Since I'm a bit of a noob to the Accord (but pretty mechanically-inclined otherwise), would you mind answering a couple of questions for me? Is the slave bleeder the only bleed point in the system? Where is the easiest access to check if that bleeder is tight? Do I need to remove anything to get to it?

Thanks for your help, I'm glad to find someone else who's had this issue. I was starting to worry a little that it might be something else (some guy on another forum said he had a similar issue but claimed it ended up being a weak pressure plate spring...that didn't make any sense to me at all).
 

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2006 I4 MT
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After pulling over, I popped the hood and noticed the rubber cover to the bleeder valve was missing and there was fluid around the slave cylinder. It was immediately obvious what happened. So I called my wife to come to my rescue with my tools and a bottle of brake fluid. I tightened the valve, refilled the reservoir, pumped the pedal to build pressure and drove home.
I always keep a set of tools in my trunk but I'm going to add a bottle of Honda brake fluid and short tubing of different sizes. I have extra unopened bottles laying around.
 

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hmm. i still have this problem but i dont think bleeder valve is problem. i still have the check valve in slave cylinder. will come out when i change clutch
 

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I've checked the master/slave system the best I can, no apparent leaks. I haven't bled it yet though, need to get ahold of some Honda brake fluid.

I'm trying to figure out a way to measure the slave cylinder position when it's occurring, to see if the slave cylinder is actually retracting without me moving the pedal.

So a question for anybody who know about these "self-adjusting" clutches: if the slave cylinder is not moving, is it possible that something within the clutch itself is allowing the pressure plate to re-engage the clutch disc?

I have read comments on various forums from several people who say that they were only able to fix this problem by replacing the clutch. I'm not questioning that this might fix my problem, but premature engagement with the clutch pedal engaged is not a normal failure mode for a traditional clutch. Just trying to understand what could be causing this if it's not my master/slave system.

FYI, several Acura forums reference this same issue (I believe the 6-speed was borrowed from the CL-type S, so I would assume the clutch is similar).
 

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Discussion Starter #9
Baldeagle,

I'm new to the forum, found it while google searching for master cylinder issues. I've got the exact symptoms you described on my 2004 Accord V6, clutch pedal gets soft and returns slow after a high-rev shift (5000 rpm and above). Sometimes it's so soft that it won't disengage the clutch again without a few good pumps. If I stay below 3000 rpm, no problems whatsoever. I can hold the pedal down in any position all day and it won't lose pressure or return slowly. I was having the same thoughts as you, "if there's a leak in my closed-hydraulic system, why is it only manifesting itself at high-rpm shifts??". I'm hoping my fix is as simple as yours too. Since I'm a bit of a noob to the Accord (but pretty mechanically-inclined otherwise), would you mind answering a couple of questions for me? Is the slave bleeder the only bleed point in the system? Where is the easiest access to check if that bleeder is tight? Do I need to remove anything to get to it?

Thanks for your help, I'm glad to find someone else who's had this issue. I was starting to worry a little that it might be something else (some guy on another forum said he had a similar issue but claimed it ended up being a weak pressure plate spring...that didn't make any sense to me at all).
Please accept my apologies for not responding sooner. Okay, this story evolved since my last post. Since that time the clutch still goes numb, but it is NOT a loose bleeder valve. The conditions are the same – run at high rpm for a few seconds and the clutch pedal loses pressure and partially falls to the floor. Pump it few a few times and it is fine. And, there are absolutely no leaks anywhere in the system.

I noticed that if I stop my car, like in a parking lot, put the transmission in neutral and hold the rpm at 5,000 for a few seconds, the clutch will lose pressure. In fact I made an appointment with my Honda Service Department and demonstrated this. (This was three weeks ago.) The service managers and a technician just scratched their heads. Apparently they had not seen this issue before. And by the way, I found several other posts in Civic forums and a Prelude forum in which owners described the identical problem. Unfortunately none of them had a solution. What’s odd is a few of those other owners mentioned they had recently replaced their clutch, pressure plate and throw-out bearing and the problem still remained or the problem started after that work was done.

I sort of digressed there, sorry. Anyway, I told my service department I was willing to pay the $1,800 for a full clutch repair IF it would fix the problem. Or, I’d also pay for a new master cylinder IF it would fix the problem. But I told them specifically, if I pay that money and the symptoms remain, we’d have major problem. As professionals, I would rely on their expertise to diagnose the problem correctly and not waste my money.

To make long story short, they could easily reproduce the problem but claimed there was no conclusive diagnosis. They could not commit my money to “exploratory surgery.” I’m sure you guys know this already, but Honda service departments share a nationwide data base that is supposed to contain information on any problem repaired by any technician. In light of the fact other Honda forums discussed the same problem, I would have bet money something about this clutch issue was in the data base. But no, there was none.

So their conclusion was my car is fine, don’t worry about it. Perhaps something will eventually fail and need replacement, providing an actual diagnosis. But until then I won’t worry about it.
 

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Baldeagle, mine does the same thing. And mine isn't a leaky master-slave system either. I did the same test, running it in neutral at 5000 rpm and the feel of the clutch pedal changes completely, gets soft and seems to begin engaging while the pedal is still fully pressed down. I had my wife rev it while engaging and disengaging the clutch, while I watched the slave cylinder and the lever that disengages the clutch on the housing. I wanted to verify that the slave cylinder wasn't retracting while the pedal was held down - it wasn't. I can only conclude that it's something in the clutch housing itself, which makes no sense. The only thing I can think of is the self-adjusting mechanism - but I have no idea how that works and how it differs from a traditional clutch (other than you can't manually adjust the engagement). I'm in the same boat as you...I'm not going to throw down $1800 for a clutch replacement if the dealership can't tell me confidently that it will resolve the issue.

Anyone know any engineers at Honda? = ) This seems to be a common enough issue that it would be nice for Honda to address it. There are several users over on the v6performance.net forums with the same issue. I've also cruised several Acura forums (the V6 Accord borrowed clutch and tranny from the CL-S), and - surprise surprise - same issue. The car shifts and drives great at low RPM's, but that's not why I bought a V6 6-speed.
 

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Discussion Starter #11
It’s a freaking enigma. Is it a vibration issue? If yes, what would vibrate and what would cause the clutch pressure to drop? I am totally clueless.
 

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I've got the factory service manual on order, I'm hoping there's a good exploded view of the flywheel, clutch, and pressure plate assembly, as well as the throw-out assembly. Maybe will give me an idea as to what could be moving, and why it only moves at high rpms. Also, I'm going to hook up a position sensor to the slave cylinder and run the wires to a meter inside the cabin. I want to know for sure that the stupid thing isn't leaking down during those high-rev shifts. Again, it doesn't appear to be when I watched it while wife was holding the revs at 5000 in neutral and holding the clutch pedal down, but I want to be positive.

Don't dealerships have some method of raising technical issues up the chain? I'm getting my timing belt done on Friday, I'll ask them if they've seen this before, or if they have any way of contacting higher-level Honda technical resources.
 

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Discussion Starter #13
I've got the factory service manual on order, I'm hoping there's a good exploded view of the flywheel, clutch, and pressure plate assembly, as well as the throw-out assembly. Maybe will give me an idea as to what could be moving, and why it only moves at high rpms. Also, I'm going to hook up a position sensor to the slave cylinder and run the wires to a meter inside the cabin. I want to know for sure that the stupid thing isn't leaking down during those high-rev shifts. Again, it doesn't appear to be when I watched it while wife was holding the revs at 5000 in neutral and holding the clutch pedal down, but I want to be positive.

Don't dealerships have some method of raising technical issues up the chain? I'm getting my timing belt done on Friday, I'll ask them if they've seen this before, or if they have any way of contacting higher-level Honda technical resources.
I know I am reaching for an explanation, but could vibrations cause the pressure plate to move? If the PP did hypothetically slide a short distance along the shaft, could that in any way cause the clutch pressure to decrease? Would pumping the clutch pedal somehow properly reposition the pressure plate?

Another potential crazy explanation does exits which I have pretty much ruled out 100%. The probability is just way too low. Theoretically, if the Honda engineers ran the clutch’s metal pressure piping very close the exhaust manifold, heat from the exhaust manifold would super heat that section of the metal line and cause the clutch fluid in that immediate area to boil. Once the fluid became a gas, it could compress and cause a pressure decrease. The idea is that high rpm creates an immediate heat surge that instantaneously boils the fluid. Clearly there are far too many flaws in that theory for it to work. If there were a design flaw like that, almost all 6-6’s would have the same symptoms. The clutch issues would become worse after the engine became hot. It would probably be a worse problem in hot climates than in cold winter climates. So I know this is a totally farfetched idea, but at this point I am willing to have an expert consider anything.

As far as raising technical issues up the chain, I thought that shared national data based was supposed help in that respect. Perhaps your Honda service department is more knowledgeable than mine. When you have your timing chain done, please create the clutch symptoms for them. Maybe they’ll know the cause. Thanks.
 

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Service manual arrived today, and I think I have now at least have a decent theory. It explains the self-adjusting function of the clutch pretty well. I quote from the manual:

"On ordinary clutches, the clutch pedal load increases as the clutch disc wears. The self-adjusting clutch is designed so the clutch pedal load will not increase even when the clutch disc wears. This is done by automatically adjusting the fulcrum of the diaphragm spring in accordance with the wear of the clutch disc. The clutch pedal load stays consistent even when the clutch disc is worn."

So basically the diaphragm spring's pivot fulcrum is designed to move further out toward the outer rim of the clutch assembly. This is supposed to be governed by a sensor spring and a compensation sprint, in accordance with clutch disc wear. However, it doesn't seem far-fetched to me that if something were worn or broken in the pressure plate assembly, the fulcrum could be moving improperly. I think this could pretty easily explain why the problem only manifests itself at high rpms, where these moving parts could be overcome by the increased centrifugal force due to the higher rotational speeds.

The ****y part of all this is there's no way to find out without the cost of a clutch replacement. Its the best explanation I've seen so far though. I guess at the very least I'd recommend that anyone having a clutch replaced due to slipping should ALWAYS have the pressure plate, disc, and flywheel replaced as a set, even if the pressure plate passes the inspection and is deemed suitable for continued use. I've read through the section on inspecting the pressure plate assembly, and it only mentions checking for bent or broken diaphragm spring fingers, and problems on the pressure plate surface. No mention of checking the self-adjustment components.

To anyone who's experienced this problem after a clutch replacement: did you replace all components (flywheel, disc, pressure plate), or just the disc?
 

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Discussion Starter #15
Service manual arrived today, and I think I have now at least have a decent theory. It explains the self-adjusting function of the clutch pretty well. I quote from the manual:

"On ordinary clutches, the clutch pedal load increases as the clutch disc wears. The self-adjusting clutch is designed so the clutch pedal load will not increase even when the clutch disc wears. This is done by automatically adjusting the fulcrum of the diaphragm spring in accordance with the wear of the clutch disc. The clutch pedal load stays consistent even when the clutch disc is worn."

So basically the diaphragm spring's pivot fulcrum is designed to move further out toward the outer rim of the clutch assembly. This is supposed to be governed by a sensor spring and a compensation sprint, in accordance with clutch disc wear. However, it doesn't seem far-fetched to me that if something were worn or broken in the pressure plate assembly, the fulcrum could be moving improperly. I think this could pretty easily explain why the problem only manifests itself at high rpms, where these moving parts could be overcome by the increased centrifugal force due to the higher rotational speeds.

The ****y part of all this is there's no way to find out without the cost of a clutch replacement. Its the best explanation I've seen so far though. I guess at the very least I'd recommend that anyone having a clutch replaced due to slipping should ALWAYS have the pressure plate, disc, and flywheel replaced as a set, even if the pressure plate passes the inspection and is deemed suitable for continued use. I've read through the section on inspecting the pressure plate assembly, and it only mentions checking for bent or broken diaphragm spring fingers, and problems on the pressure plate surface. No mention of checking the self-adjustment components.

To anyone who's experienced this problem after a clutch replacement: did you replace all components (flywheel, disc, pressure plate), or just the disc?
Hi Stevie. Interesting theory. I suppose it is plausible. I wish I could better understand the link between the fulcrum and loss of pressure. Also, this makes me wonder how much this fulcrum must move to explain the degree of clutch movement I experience. And why would pumping the pedal return it to normal? What exactly resets? I tend to agree this is the best explanation yet. Good work!
 

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Sounds like a legit possibility to this issue. If the pressure loss isn't coming from the slave or leak, pressure loss has to be coming elsewhere the spring mentioned in the theory above sounds reasonable to consider.
 

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Well, I have no experience with Honda clutches, but I have lots of experience with hydraulic operated clutches and clutches in general. First thing, vibration may make something come lose, but it won't tighten it back up again. So if it came lose it was leaking and all it could do after that is come loser, and leak faster.. Every time you used the clutch you were effectively pumping it back up, and also squirting out just a little more fluid. Sooner or later you were going to run out. If someone pushes in the clutch pedal and the slave cylinder does not respond it means one of three things. First is that fluid is leaking past the seal in the master cylinder and so no (or very little) line pressure is being created. Two, there is a break somewhere in the line between the master cylinder and the slave cylinder, or; three; that fluid is leaking past the seal in the slave cylinder. Those are the only things that can be going wrong.

As to the question about "self adjusting clutches", well, all hydraulicly operated clutches are self adjusting. It is just like disk brakes, as the contact material wears down (and clutch linings and brake pad linings are exactly the same stuff) the activating parts have to move farther. What happens is the piston in the slave cylinder moves farther down its bore, or the piston in the caliper moves farther out its hole, and that is how the adjustment takes place. Its why you have to put a C-clamp on the piston of the caliper to push it back in when you put new pads on. Well, the slave cylinder on the clutch does the same thing as the clutch wears.

As to the problem of the clutch hanging up after prolonged high RPM, I think that is a symptom of an old clutch who's diaphragm spring is losing its ability to return to its formed shaped. It was a common problem with old GM clutches, back in the day, as they say. The design of the clutches hasn't changed a bit since then.
 

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White on Black AV6-6
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I replaced my clutch and flywheel and all issues went away.
Clutchmasters fx350 stage 3.5 with solid lightweight aluminum flywheel

Cost me around $1300 for this and I paid my friend mechanic $400 to help me so if you are willing to spend the money ditch the OEM replacement and upgrade. No issues with the Single Mass Flywheel.
 
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