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Old 11-27-2019, 07:22 AM   #1
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Slave cylinder, maybe more?

Greetings,

I purchased a 1999 Boxster a few months, but have been having a consistent issue.

Car history is largely unknown so I am assuming the worst and working to address any issues we find or known concerns. It is a rust free California based (formerly) car and is in generally good condition with 130k miles.

My issue is that the slave cylinder has blown 3 times in the past <200 miles. Obviously,

1) I have found two straight "bad" slave cylinders (not terribly likely)
2) I was doing something incorrectly installing them
3) Something else is also an issue or is causing the failure of the slaves

The "original to me" slave cylinder broke in less than 100 miles after we obtained the car. It popped after starting from a light in first gear. Car was warm and clutch went to the floor and stayed.

The second slave cylinder broke in a similar manner when starting the car after one trip of about 20 miles.

The third broke after an even shorter trip from a mechanic who changed the cylinder, again when starting the car.

General observations are limited since the car is new to me, but the clutch seems a bit heavier than I would expect, but seemed to run smooth. The clutch pressure decreased a bit with both of the new slave cylinders, but only slightly.

I am unsure what other information may be helpful, but can offer any responses possible with the limited experience with this particular car.

Please let me know if anything else may be the issue.

Thank you.

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Bill

1999 Boxster with manual trans used daily driver and HPDE
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Old 11-27-2019, 08:53 AM   #2
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sounds like the issue is elsewhere. If you can confirm that the fluid system pressure is normal (not sure how), then it might be that you have a bad pressure plate or issues with the throwout bearing or arm it resides on. I haven't heard much about master cylinder failures but is suppose if something is wrong there it could cause problems.

Does the clutch disengage smoohtly/easily?
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Old 11-27-2019, 09:06 AM   #3
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The clutch seems to operate smoothly and engage well. I haven't had a chance to use it as much as i would like (lol) and not a lot of experience in that car unfortunately.
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Old 11-27-2019, 09:11 AM   #4
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In what manner are they failing? you used the word "pop"?
I think the failure can only be caused by two things, really: Over-Pressure blowing seals, or over-extension pushing the ram/piston out of the cylinder.

I think over-pressure is unlikely, given the little I know about hydraulic systems. I'm leaning to over-extending. I wonder if it's possible that the arm holding the T/O bearing is off it's fulcrum, and this is allowing the piston to just keep traveling well beyond its design?

I dunno..... I'm making this up, since I've never run into this before.

I guess the third possibility is that you DO, in fact, have multiple bad units. Are you switching brands? Or are you using the same brand over and over? if so: WHAT brand?
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Old 11-27-2019, 09:17 AM   #5
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The slave cylinder is bursting/leaking, which leads to the clutch pedal going to the floor and staying there.

I was wondering (along the same lines) if the "starter switch" at the bottom of the clutch is too far and maybe leading to the issue. Not sure if that is possible and/or adjustable, but it has come to mind.

I am not sure what brand the slave cylinders are, but will check in the garage when i get back tonight.

Thanks again for all the help.
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Old 11-27-2019, 09:52 AM   #6
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Quote:
Originally Posted by maytag View Post
In what manner are they failing? you used the word "pop"?
One time on a recently installed gearbox the slave wen't "pop" and the pedal went to the floor getting the brand new clutch disc completely wet on hydraulic fluid...

It seems that I failed to fully seat the 'plunger' from the slave into the cavity of the fork and as soon as I pushed the pedal it went down..a real mess and everything had to come apart again.

But if you managed to drive a few miles before the failure occur then most likely you got NOS (new old stock) slave that had dried rubber seals that failed under pressure.. that would be my guess
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Old 11-27-2019, 10:10 AM   #7
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Thank you. Hopefully, that is true. I feel like we are causing a local stock out condition on Boxster slave cylinders in our area. Its almost like the weatherman said its going to snow and everyone went out and got their bread, milk, and eggs, and slave cylinders.
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1999 Boxster with manual trans used daily driver and HPDE
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Old 11-29-2019, 01:20 PM   #8
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If you're blowing the end out of the slaves, I would guess that the piston is over extending. This can be caused by a problem with the clutch release fork being bent or misaligned. Take a peek with endoscope or an inspection mirror to verify that the dimple in the fork is aligned with the centre of the mounting hole. If not, then you'll have to pull the transmission and check the fork retaining clip (pivot) and other parts. I discuss this in my video on my YouTube channel: https://www.youtube.com/watch?v=mfqpCgDGJhk&t=3s
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Old 11-29-2019, 02:53 PM   #9
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Quote:
Originally Posted by NewArt View Post
If you're blowing the end out of the slaves, I would guess that the piston is over extending. This can be caused by a problem with the clutch release fork being bent or misaligned. Take a peek with endoscope or an inspection mirror to verify that the dimple in the fork is aligned with the centre of the mounting hole. If not, then you'll have to pull the transmission and check the fork retaining clip (pivot) and other parts. I discuss this in my video on my YouTube channel: https://www.youtube.com/watch?v=mfqpCgDGJhk&t=3s
Yup, this is exactly what I was getting at too.... you explained it much better. ;-)



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Old 12-02-2019, 09:35 AM   #10
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Thank you for the explanation. At least I have a few more things to look at now as opposed to potentially replacing the slave and hoping it doesn't break, again.

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