Pressure plate failure?

[mmendes]

I recently went to replace the clutch slave cylinder on my 1972 240z with a 4 spd transmission becasue the clutch was slipping on the street. By slipping I mean that with the pedal fully depressed the car would still try to lurch forward when in gear. Neutral was fine. Ive only put about 1200 miles on the car since ive had it but its always been difficult to shift.

I bled the clutch slave cylinder that was already installed and tried adjusting the slave cylinder rod with no improvement in the clutch engagement, both feel or physically disengaging the clutch all the way. The fluid coming out of the old system was pretty black so I decided to replace the slave thinking there was a bad seal, it was super cheap and already apart.

 

After removing the old slave cylinder and testing out the clutch release fork I found very little resistance and I could easily move the fork through, what looks to be, the full range of its travel with just my hand. Video attached, im thinking I need a new pressure plate. OR the PO has an aftermarket clutch installed and did not use the longer throw out bearing I've read you need for a centerforce

 

https://youtu.be/keKrmlkZRxk

[NewZed]

You have a couple of things backward.  What you describe isn't "slipping" it's lack of disengagement.  The opposite of slipping.  And you're moving the fork in the wrong direction in your video.  But it still looks a lot like a short throwout bearing collar.  The fork is very close to the end of travel before it would even start moving the pressure plate.  From what I've seen the fork is about centered in the hole when it's sitting on the pressure plate fingers, on a proper system.  Yours is way back, close to hitting the edge of the hole.  I actually have a measurement somewhere, I'll see if I can dig it up.

 

You probably need to take the transmission out and get a longer collar.  MSA has them.  Type "clutch collar" in the search box.

 

http://www.thezstore.com/store/merchant.mvc?Screen=SRCHM

[NewZed]

Here it is.  This is with the clutch fork just about to move the pressure plate.  The bolt head is the one on the slave cylinder.

 

 

[mmendes]

I suppose dragging may be the better term? Regardless you nailed the symptom I was referring to. 

 

I will take some measurements when I get home.I think you confirmed what I suspected though. You have a boot covering yours in the pic, in the video I can move the clutch fork against each side of the hole in the casting without feeling ANY resistance. So I also have a L28E and 4spd in the barn, would the throw out bearing from that work? I read that a few others have used OEM nissan parts as well.

 

Man I was really hoping to save some money for some dampers that actually work at my ride height.

But while im in there.... Any recommendations on trans fluid or any other seals, bearings I should replace? The history of the drivetrain is unknown so ill also probably take the time to figure out what parts it was built with. Thanks for the help.

[NewZed]

There is a variety of sleeves/collars out there, to match the various pressure plates.  That's the key, the pressure plate and sleeve need to work together.  The bearing fits in the sleeve and is replaceable.  

 

Many of us have found that a distance of about 92 mm from the surface of the flywheel to the surface the fork rides on, the two ears on the sleeve, when the parts are stacked, will always work.  You'll find advice on mixing and matching by year of car and/or transmission but once the clutch has been replaced you're basically starting from scratch.  Most new pressure plates are the short ones that require a long sleeve.  Somebody probably kept the old 240Z sleeve with a new short pressure plate on yours.

 

You could get the barn parts ready to swap on, then just do the sleeve if you find that it will work.  Use the L28E fork also, with a newer type slave and rod.  You still have the old adjustable type slave and fork.

 

Attached a picture.  Not exact but gives the concept.

 

[mmendes]

Hmmmm so I couldnt get a picture with just my two hands but I am at roughly the same distance from the salve as I begin to see pressure. From the nut I start to feel pressure by hand at 6.35mm, yours looks dead on 6mm. I grabbed my crowbar to get some leverage on it and could feel some actuation. I could move it a little more than half an inch with maybe another 3/16 to go to the end of the hole

 

Think I can make up the distance with a new slave, bled properly and an adjustment on the pedal? im going to need all the travel though? Uggh it might not be RIGHT but it does sound better than pulling the motor in the cold, when its just about to sit for 5 months... 

[NewZed]

Actually, that's 6 cm.  60 mm.  You could adjust the rod out as far is it will go or even make a new one from an old bolt.  People have done it before.  Worth a shot.  Or put a spacer between the rod end and the fork just for a short experiment.  If it disengages you'll know there's hope.

[mmendes]

Ya. gotta stop updating while im staring at things at work. Feel like such a newbie with this car, first time I've really had to fix anything. I will report back whether 6.36cm is not enough travel for someone down the road who might have the same problem.

 

Thanks for your help.

Edited November 12, 2016 by mmendes