Replaced the clutch accumulator

[Chuck Jones]

There have been some posts on the forums about a high frequency vibration in the clutch pedal as you barely push on it. No one has come up with a good answer to the source of the vibration....but the consensus seems to be the fingers on the clutch mechanism will vibrate at a certain rpm...nothing to worry about. I thought it was either my clutch slave or the accumulator.

Well, finally, my accumulator went out and I replaced it today...it's up inside the drivers side front of the engine and is a black cylindrical object....you can access it from underneath. I thought that perhaps that was the source of the high frequency buzz in the clutch pedal.....but it's not....so I'm back to accepting the "fingers" theory. I've spoken to a number of turbo owners as well as owners of other high end sports cars, and some report the same feeling. I've decided to adopt a "not to worry" attitude.

[wross996TT]

Come on Chuck, get that GT3RS clutch package and LWFW....no vibration here.

[Chuck Jones]

Now that I've been led down the primrose path with a flash and upgraded wastegates, (which I said I wasn't going to do)I'm afraid that the clutch will be the next item....insofar as the light flywheel goes.....I'm really not sold on that since I dont' track and really dont need that instantaneous spoolup. The flash and wastegates along with the other upgrades I've already done will hold me over.

You guys are like Fritos salesmen....becha' can't have jes' one. Ok...maybe it's not Fritos.....

[wross996TT]

That would be lays potato chips

[Chuck Jones]

OK Wild Bill:

You threw down the gauntlet....since you indicated that the correct product was "lays" rather that Fritos....I would point out that since Lays is a proper noun which references a patented and specific product name, the correct way of presenting it is with a capital "L" rather than lower case....hence, it's Lays....

I rest my case, and retreat to the recesses of cyber space.

[wross996TT]

i don'T capitalize aNything beCauSe oF the RuLES

Cheers cHUCK

Edited July 31, 2008 by wross996TT

[jpflip]

I cannot believe it Chuck but I replace both unit yesterday and now I got this strange pedal vibration when I am depressing the clutch. I did not have this symptom with the previous slave or accumulator. I will do a longer test drive later this week and probably will try a deeper bleeding of the system.

[Chuck Jones]

JP: That's interesting becasue you never had it before the replacement. I'm going to be following your comments closely becasue this vibration issue seems to be fairly common....but no one has been able to put their finger on it. The usual comment or assessment is that it's the fingers on the clutch that vibrate at a certain rpm. Do you get it at a certain rpm, or is it constant?

I sure wish someone could track it down becasue there are quite a few of us who have it...and a good number who don't. When you say vibration....is it just as you depress the clutch pedal at the top of the throw? Just as you start putting pressure on it to push down the pedal? You should feel the buzzz...sort of a very high frequency vibration in the ball of your foot as you start to press the pedal.

Very curious indeed...and somewhat annoying really.

[jpflip]

I have split the accumulator in half to found out what can fail in this simple reservoir. The rubber seems to be of a good quality but in my case it split at the joint between the top bell portion and the base. It is a bladder type accumulator and I guess there was previously pressure on the other side of this bladder but before cutting it in half I have drill a small hole to release the pressure and nothing came out so I am sure the accu was at fault in my case...On aircraft accumulator you can recharge the nitrogen side but as soon you open the pressure valve and you got hydraulic comming out you know the bladder failed....

The bell is cut in half and I also cut the bladder or diaphram.

Now you see my failure on the joint portion the rubber is completely off at the base or the split and cut at several places...Weaken by the hydraulic ??? May be...

[RFM]

Chuck

As you know turbo pressure plates are different in construction as the water cooled Carrera's, they looks and use approx. the same system as the former air cooled engines ( the pressure plate is pulled by the bearing, bearing is spring loaded installed in the middle of the plate at the end of the diaphragm fingers, and not pushed )

I noticed during the years, that in most cases of vibrations in the clutch pedal, both fingers ends of the release lever that grabs the release bearing get a small different thickness by use which result in vibrations. If you replace the bearing and the lever on a clutch job as well, you never will have a vibration problem.

[jpflip]

Chuck

As you know turbo pressure plates are different in construction as the water cooled Carrera's, they looks and use approx. the same system as the former air cooled engines ( the pressure plate is pulled by the bearing, bearing is spring loaded installed in the middle of the plate at the end of the diaphragm fingers, and not pushed )

I noticed during the years, that in most cases of vibrations in the clutch pedal, both fingers ends of the release lever that grabs the release bearing get a small different thickness by use which result in vibrations. If you replace the bearing and the lever on a clutch job as well, you never will have a vibration problem.

I realized the post is not for me but...I didn't know about that thanks for the info but how can you explain that suddenly after replacing the slave + accu I got this vibration. May be it is because I got more space between the piston end and the fork itself... I am talking about millimeters here...I did not compare both slave before installation. I should measure the total length of both before installation. Toooo bad....

Edited August 2, 2008 by jpflip

[Chuck Jones]

At this point, I'm just going to live with the slight "buzz" on the clutch pedal till I eventually need a clutch...and with the new UMW tune, that might be sooner than I anticipate....there have been a lot of threads on this issue...and most folks seem to say that it won't hurt anything and just drive it.....but I'm a guy who watches gauges and is constantly in touch with the sounds and feel of the car...so a vibration is something that puts me on alert...and it just shouldn't be there in a finely tuned Porsche even if the P car dealership says it's no big deal...

[dragonvision]

There have been some posts on the forums about a high frequency vibration in the clutch pedal as you barely push on it. No one has come up with a good answer to the source of the vibration....but the consensus seems to be the fingers on the clutch mechanism will vibrate at a certain rpm...nothing to worry about. I thought it was either my clutch slave or the accumulator.

Well, finally, my accumulator went out and I replaced it today...it's up inside the drivers side front of the engine and is a black cylindrical object....you can access it from underneath. I thought that perhaps that was the source of the high frequency buzz in the clutch pedal.....but it's not....so I'm back to accepting the "fingers" theory. I've spoken to a number of turbo owners as well as owners of other high end sports cars, and some report the same feeling. I've decided to adopt a "not to worry" attitude.

Say Chuck, where is the accumulator? Mine is leaking - 996 2002 turbo.

thanks,

kerry

[contigo]

I am doing the Evoms Gt2 kit next week , do I need to put the engine and gear box down to do the work or just by lowering it a little?

[benaslan]

I have my car in the shop for my transmission (other post) and they noticed this sound as well with the clutch pedal depressed. They said the cause is the valve in a hydrolic hose (do not remember exactly) but I just sent the service guy an email asking what is being done. and can repost if you wish. I remember him saying that it is a big deal as it can lead to other bigger problems if unattended to.

[Loren]

I have my car in the shop for my transmission (other post) and they noticed this sound as well with the clutch pedal depressed. They said the cause is the valve in a hydrolic hose (do not remember exactly) but I just sent the service guy an email asking what is being done. and can repost if you wish. I remember him saying that it is a big deal as it can lead to other bigger problems if unattended to.

There are stories of the power steering hose fitting breaking and spraying Pentosin on the hot exhaust starting a fire.

There a fellow on Rennlist about a year ago that had that happen to his Speed Yellow 996TT. The pictures were not pretty.

[Chuck Jones]

Loren is right about the hydraulic hose to the power steering....this appears to be a more common failure than we'd like to see...and is something you don't want to mess with. There have been a number of unfortunate car fires as a result of that hydraulic fitting failing (usually accompanied by a high pitched whine) spraying Pentosin around and it it highly flammable....resulting in an engine fire.

With regard to the vibration in the clutch pedal, I believe jpflip is right. If you find a picture of a clutch setup, you'll see that the pressure plate has a number of "fingers" on it that engage when you depress the clutch. I think that some cars pick up that slight vibration of these little fingers more readily than others. I did eventually run out of clutch and installed the UMW replacement, and the vibration "almost" went away....it's much less noticeable, but because I'm really tuned into it, I can detect just the slightest hint of it still there.....I believe it's the fingers on the pressure plate and nothing to fret about. Sometimes we Porsche folks have a tendency to make much ado about little or nothing.

[jpflip]

I am doing the Evoms Gt2 kit next week , do I need to put the engine and gear box down to do the work or just by lowering it a little?

I hope you got all the PDF"s files for the installation of the kit. No you don't have to lower the engine or the gear box according to the files....