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Old 04-26-2014, 07:13 AM   #1
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Clutch not fully disengaging - why?

I've determined that the clutch on this 1998 manual transmission is not fully disengaging. That is why, with the car in reverse, and the clutch pushed to floor, that when turning the key to start the engine, the car moves backward a little as the car starts. Further, the clutch action (engaging, disengaging - as little as it does) happens close to the floor.

I've bleed the clutch properly. Upon closer examination of the clutch line, I did find a pinch, not a block, but certainly the flow is impacted. Now, I need a specialist is hydraulics. is the flow just slowed, or is the flow actually less because of the pinch?

My opinion is that the flow is slowed. That a full push of the pedal will push the same amount of fluid through the line, but not a fast because of the smaller diameter of the line at the pinch. But, if I'm wrong, then the lesser amount being pushed may explain why the slave cylinder is not moving its rod enough the fully engage/disengage the clutch. Keep in mind too, I believe there is a power assist to the clutch, just as there is a power assist to the brakes. They do after all, share the same reservoir. Am I correct about the clutch being power (vacuum) assisted?

Certainly there is an Engineering graduate who had hydraulics that has grown up to own a Porsche. Help this commodity trader out.

Thanks,
Joe

Last edited by Xcellr8; 04-26-2014 at 07:17 AM.
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Old 04-26-2014, 07:36 AM   #2
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when holding the pedal to the floor is there a loss of hydraulic pressure (i.e. does the clutch begin to engage more)? this would indicate bad seals in either the clutch master cylinder or slave cylinder. is there an adjustable rod on the slave cylinder? which you can use to apply more pressure to the clutch pivot arm? what is the clutch pedal height? if it is too low it may need to be adjusted to give you full disengagement. last, did you do any work to the system before it began to give you problems? generally the first point of failure on hydraulic clutches is the slave cylinder.
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Old 04-26-2014, 07:37 AM   #3
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If you really think the line is pinched enough to hinder the flow... replace it. Lines are easy to make and all the auto parts stores have them.

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Last edited by healthservices; 04-26-2014 at 09:03 AM.
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Old 04-26-2014, 07:46 AM   #4
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My son's first Miata had this exact symptom, clutch would not fully disengage when clutch pedal was depressed. Turned out to be a leaky slave cylinder. He was actually losing hydraulic fluid though. Our next thing to investigate would have been the clutch master cylinder (shared on the boxster with the brake master cylinder) - if the seals go bad then it can let fluid back into the master that should be used to keep the clutch disengaged.

Are you losing any brake fluid?

If you squeeze the rubber boot on the clutch slave cylinder (the part that flexes when the clutch engages/disengages) does any fluid come out? if so then it is a bad slave cylinder.

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Old 04-26-2014, 08:26 AM   #5
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Really appreciate all the help. To answer some of the questions;
- There is no fluid leaving the system. No drips or puddles.
- The clutch does NOT appear to disengage more as the pedal is held in for an extended time.
- The problem is way more noticeable in reverse than in first, i.e in reverse even with clutch pushed in, the car is moving backwards. In first, when the clutch is pushed in, the car will roll to a stop.
- If there is adjustment on the slave cylinder, I don't know it. How would I do that?
- Similarly, if there is adjustment on the clutch pedal, I don't know that either. How would I do that?
- The only work I have done to the car is to bleed the clutch using Motive pressure bleeder. The car is new to me and was purchased sight unseen through third party so previous owner is not known.
- I would replace the line, or repair the line, if I knew that would fix the problem. But, no engineer in fluid dynamics has convinced me that a pinch in the line is the problem. The idea of repairing the line is a fair suggestion, but this doesn't look like brake line, it appears to be a much larger diameter, so I'm not sure repair parts are as readily available as implied, though to be fair, I have not checked. Anyone know what diameter I would need?

Thanks again,
Keep the ideas coming,
We are at least eliminating some areas.
Joe
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Old 04-26-2014, 08:42 AM   #6
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You need to replace the clutch, and pressure plate at the very least. There is a plastic pivot on the throw out arm that wears overtime the throw out bearing face wears over time, the fingers on the pressure plate wear over time, and in some instances the fingers on the pressure plate bend. All these items add up to not enough travel. A bad clutch and pressure plate do not always mean the clutch slips.
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Old 04-26-2014, 08:54 AM   #7
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Even if the tube is pinched 50% closed. The clutch master cylinder pushes an equivalent volume of fluid to the slave cylinder. If you have no air and you have bled the system, then the slave cylinder receives that fluid. The only change is the fluid runs faster through the pinch point than the rest of the system. The physics of it is under a given pressure a difference in area changes flow velocity at the point of restriction. An ounce of fluid displaced from the master cylinder will still cause an ounce of displacement on the slave cylinder.
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Old 04-26-2014, 09:06 AM   #8
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And I agree with js... I think its going to need a clutch.

Get it done and start having fun with the car again!

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Old 04-26-2014, 11:52 AM   #9
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the slave has no adjustment and it's a cheap part at about $50
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Old 04-26-2014, 04:07 PM   #10
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Quote:
Originally Posted by jsceash View Post
You need to replace the clutch, and pressure plate at the very least. There is a plastic pivot on the throw out arm that wears overtime the throw out bearing face wears over time, the fingers on the pressure plate wear over time, and in some instances the fingers on the pressure plate bend. All these items add up to not enough travel. A bad clutch and pressure plate do not always mean the clutch slips.
+1
Had the same symptoms in my 996 and ended up changing the clutch. Everything was/is fine now.
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Old 04-26-2014, 07:47 PM   #11
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Okay, Okay.

Thanks again for everyone's help. My wife would say since I'm now hearing what I don't want to hear, I'm tuning out. True, I do not want to replace the clutch. That fear however has motivated me to replace the pinched line, and since I'll have the hydraulic system open, the slave cylinder too.

There is an update. I massaged the pinch - a tap here, a squeeze there - trying to open up the line a bit more. Then when test driving the car, the disengage problem was still present and noticeable in reverse. However, once the car was in the street and I turned it off, put it into first, pushed the clutch in, and started it up, I took off and was able to shift into second by double clutching. Never did that before, but I'm not sure I tried it double clutching it before. Could not downshift at all. Double clutching, triple, pushing it five times, could not downshift.

I posted a WTB ad for the clutch line segment that has the pinch. If you have a parts car, send me a PM with a price shipped to Decatur, IL 62526.
Thanks, Joe
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Old 04-26-2014, 08:14 PM   #12
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Just a wild, but basic, thought. Have you checked your motor mount to see if it is dried out, or has cracks in the rubber portion?

That can cause shifting problems, and since you have bled the system, it may be something to consider.

If it's OK, just keep your head in the sand...................

Just sayin'.....................

TO
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Old 06-13-2014, 07:23 AM   #13
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Correct me if you have a theory

Update - having replaced the pinched clutch line and the slave cylinder, there was no difference in shifting (Or should I say lack of shifting.)

Worn out fingers on the pressure plate is moving up the list of possibilities, but I can't reconcile how the car was driven upto this point. Isn't it true that the fingers would have worn out gradually? Which I would think would cause the shifting to become more and more difficult gradually. The condition of the shifting today is so poor that a driver would never have gotten to this point. The car is not drivable in traffic. To downshift you have to shut the motor off, put it into the gear you want, then restart the car. Tony Stewart might be able to do it save gas the last few laps of NASCAR event, but not everyday. I think what happened to this clutch/transmission happened all at once and that does not sound like gradual wear.

Correct me if you have a theory.

Thanks,
Joe
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Old 06-13-2014, 08:57 AM   #14
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Definitely need a new clutch... Any one wanna take bets?

OP- sorry man, must stink since it seems you just got her...
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Old 06-13-2014, 11:36 AM   #15
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this is what i found when i dropped the trans last week.
the clutch was not slipping, but also was not disengaging properly.






slave cilinder was toasted as well.
i guess when the fork bent, the hydraulic pressure pushed it over its limit.
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Old 08-23-2014, 05:51 PM   #16
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Damn I think I might be at this exact same point.

I've bled the clutch and replaced the clutch hydraulics. It seems to work better but not perfectly each time but engaging reverse on flat ground is exactly like the OP states. I've been hoping it's just more air in the system but did a search before I posted anything new.

Looks like I'll be getting to that IMS sooner than I'd planned, but at least I'll have it behind me and know where I stand.
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Old 08-12-2015, 06:19 PM   #17
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I just went through a similar situation and want to document for you guys what happened.

I noticed a leak on the garage floor then the clutch soon begins to not fully return to the up position.

I figure its the slave unit at 122k miles on a 1999.

The mechanic changes the slave and the first one blows off during testing.
Upon checking further the pressure plate is shot and fork bent.

I ended up getting a SACHS clutch kit from fleabay for $345 along with a master and slave unit for less than $450 total for all and Im talking all German OEM not chi-com knock offs.

They polished off the flywheel too.


My IMS was changed out earlier by the first owner so no worries there! Whew!

Got all fresh fluids and seals.

I got the car back and she shifts like a hot knife through butter - WOW!

I got away cheap for this kinda work - if you guys are in ORANGE COUNTY, CA

Definitely check out TOP END OC Motors in Costa Mesa/Irvine off Redhill. Ask for Matt or Eric. They even have loaner cars or rentals at no extra cost.

They let you buy your own parts and will do the work so you can save the most $$$!

Last edited by Specwar; 08-16-2015 at 01:04 PM.
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