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73 240Z Slave Cylinder - Hyperextends, Pushes Out of Cylinder


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#1 Mitchell

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Posted 24 November 2017 - 02:55 PM

Anybody had the following problem with slave cylinders on a s30 73 240Z. I've had this car 30 years and have replaced slave cylinders many times. I hadn't been driving my car for about 3 years. I was test driving the car with the slave cylinder which had been used for a few years before the car was parked for the 3 year rest. While shifting into 1st gear the slave 'hyperextextended' or pushed out too far causing the piston in the slave to wedge at an angle between the slave body and fork. I was able to loosen the slave bolts and put the slave piston back into the slave cylinder. But it did the same thing again. I replaced from Rock Auto the Clutch Master and Clutch Slave together. Both parts look the same, 5/8" bore master the same as the old master as well as the slave looks identical. It's still doing the same thing with the new Master and Slave, just as the system is completed being bled. In other words the piston hyperextends to the point where it wedges at an angle with the rod between the fork and slave cylinder body. Could the shifter fork cracked or broke inside the tranny, however, it doesn't rattle or feel loose? I can pump the system by hand using the fork against the pushrod. I've tried in both directions, the old rod, the new rod, with the new slave reversing the attachment of the bleeder screw and hose fitting. No difference. This is and has always been the Non Hole, non threaded push rod late style S30 setup. Could really use some help. Thanks, Mitchell



#2 Roadster-ka

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Posted 24 November 2017 - 03:12 PM

If you're positive the slave is correct, you need to pull the transmission and inspect all related parts that disengage the clutch. It may be the clutch arm itself or the pivot ball.

#3 Mitchell

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Posted 24 November 2017 - 03:18 PM

Thanks for the quick reply, not the best news I hoped for.... I'll let everyone know once this gets resolved.



#4 Mitchell

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Posted 24 November 2017 - 03:31 PM

Would you know the amount of space or if It's possible to access the pivot ball and the clutch arm, separating the engine from the transmission without taking the transmission and motor out?



#5 datzenmike

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Posted 24 November 2017 - 05:00 PM

Carefully peel the shift arm boot out of the transmission and slide it out on the clutch arm. With a flashlight you should be able to look in on the rear side of the arm and see where the ball rests inside the arm.
 
By what I read this was working just fine and the only thing that's happened is it has sat for an extended time. Then it was taken out and driven. I assume it worked then as well but then stopped working?
 
If the piston came all the way out then the arm just had to have over extended to allow this also. So what would cause that? The clutch arm is like a teeter totter. As the slave pushes outward to the rear the release bearing pushes forward against the clutch diaphragm fingers.
 

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See the two ends of the fork? The two shiny patches are where it bears against the release collar.

 

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 They clip to the back of the release bearing collar with a simple wire spring. Now if that wasn't installed properly and slipped off, or the wire clip broke, the fork could slip off and move forward unopposed and the slave piston would easily over extend and fall out.


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#6 Mitchell

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Posted 24 November 2017 - 05:52 PM

Mike, Wow, you really now these cars, that sounds exactly like what it is, very likely to me. You read this right, all was well before the car was put up. Problem began during the most recent test/exercise drive 3 years later. Looks like I'll need to look at renting or buying a crane to get the motor and transmission out to check the wire clip situation and deal with it outside of the car, not like working on the 620.

 

Thanks Very Much for the insight...

 

I'll let you know once I get it apart and post a few pics.

 

Best Regards,

 

Mitchell



#7 datzenmike

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Posted 24 November 2017 - 06:55 PM

Hey it's just a guess. :lol:

 

Again if you take the boot out you may be able to confirm this by looking with a flashlight and wiggling the arm. If it is off I wonder if it could be put right with a long screwdriver.


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#8 Mitchell

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Posted 24 November 2017 - 07:38 PM

Between all of the tries, must have bled 2 quarts of brake fluid through the system in all of the attempts. You're right I should try to inspect at least before rushing to get the crane. 



#9 compression

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Posted 23 April 2018 - 08:48 PM

One a car project years ago (240sx) I made a longer push rod shaft for my slave cylinder. I cut the shaft of an old cheap screwdriver to the length I needed then rounded the ends with a grinder and it worked well!

Not sure if it applies here, just something I remember doing.  I believe it was due to an afermarket HKS flywheel, that had been re-faced a few times.


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