Clutch failure?

[IdahoKidd]

Recently I have installed a 5 speed into my 77 280z. At the time, I put in a new clutch, pressure plate, and throwout bearing. The clutch and pressure plate were new in a plain brown sealed box but were at least 20 years old. (Came with the car with other "spare" parts.) Everything went well now for a couple of months. Recently it has become difficult to shift from neutral into gear and reverse seems to be the worst. The clucth isn't disengaging enough and the tranny wants to grind. Double clutching seems to help when rolling. So, I changed out the clutch master and the slave to be on the safe side. No change. There is about a full inch of movement on the clutch fork from the slave (measured at the slave). The car begins to move the instant the pedal comes off the floor. Much to close to the floor I believe. No adjustments I seem to make make any difference which leads me back to the pressure plate. It is a diaphram style. Is it likely the diaphram is collapsing instead of releasing the pressure on the clutch? I can't come to any other conclusion...

BTW, there is NOT enough room under the pedal assembly for a 230 lb guy laying on his back with feet over the top of the back of the seat AND a teenage kitten that wants to play with the wiring harness while trying to get that pos pin and clip into the linkage. Without the newly relocated and imprisoned cat, it still took nearly an hour to get the pivot pin back in. I was approaching the max depth of the love for the car.........ugh!

[Nigel1943]

I'm assuming you had a 4 speed tranny in before. The most likely cause of your problem is that you have the wrong clutch/throwout collar combination for a 5 speed.

[IdahoKidd]

Correct, I went from 4 to 5 speed. I definately had the wrong one in the first time as the clutch fork wouldn't even move. Took it right back out and changed the fork and bearing. Everything worked fine for a couple of months and then the cluctch sort of faded away making me think the master or the slave wasn't holding pressure or fully depressing the pressure plate. Now I am thinking the springs in the pressure plate are stronger than the "fingers" that leverage them open. (not a true finger pressure plate-not sure what to call the diaphram part). Changing out the clutch is a bit of a PITA so I am trying to be sure I haven't overlooked the obvious.

[Arne]

Changing out the clutch is a bit of a PITA so I am trying to be sure I haven't overlooked the obvious.

Really? I've found that dropping the transmission on my 240Z is probably one of the simplest and easiest cars to do that on that I have ever owned. I can do a clutch in my garage on jackstands in 3-4 hours, tops.

[240Z-Fan]

...Everything worked fine for a couple of months and then the cluctch sort of faded away making me think the master or the slave wasn't holding pressure or fully depressing the pressure plate.

Did the problem change at all when you installed new parts? Did you try rebleeding it?

It is *possible* something in your 20 year old clutch failed. But I kind of doubt it. The friction face could delaminate, but it wouldn't take too long for it to completely fail after that.

Another possibility is that the clutch disc hub is stuck or dragging on the transmission input shaft. If the disc is stuck on the shaft, it can't move away from the flywheel when you unclamp it. Was the shaft rusty when you installed the new clutch? It doesn't take much dirt, debris or rust to cause it to hang up. Greasing the shaft VERY lightly is good. But too much grease on the shaft will act as a dirt magnet too.

Al

[Nigel1943]

Correct, I went from 4 to 5 speed. I definately had the wrong one in the first time as the clutch fork wouldn't even move. Took it right back out and changed the fork and bearing. Everything worked fine for a couple of months and then the cluctch sort of faded away making me think the master or the slave wasn't holding pressure or fully depressing the pressure plate. Now I am thinking the springs in the pressure plate are stronger than the "fingers" that leverage them open. (not a true finger pressure plate-not sure what to call the diaphram part). Changing out the clutch is a bit of a PITA so I am trying to be sure I haven't overlooked the obvious.

So, do you know what clutch/throwout collar you have in now? Is it a 225mm clutch or a 240mm?

[JohnnyO]

I can do a clutch in my garage on jackstands in 3-4 hours, tops.

Why don't you pack up your tools and head to Iowa? Here's the directions:

http://www.mapquest.com/maps?1c=Springfield&1s=OR&1y=US&1l=44.046398&1g=-123.020798&1v=CITY&2c=Moscow&2s=ID&2y=US&2l=46.732498&2g=-116.999199&2v=CITY

Kidd could really use your help!

[Zed Head]

If you could watch the clutch fork while you press the pedal (a mirror beside the car maybe?), or have someone watch it, or film it, or put an indicator on it - then you could isolate the the hydraulic side of the clutch system from the mechanical side (inside the bell housing).

Then you would know if it's the clutch disc or pressure plate vs. the master or slave cylinders.

More - if the fork moves but it doesn't release, it's pressure plate or disc. If it doesn't move, cylinders or pedal mechanism

More #2 - or you might be able to get under the car, lever the clutch fork with a wrench or some pliers and see if it disengages. A wheel or two would need to be off the ground and the car in gear, while you moved the clutch fork and turned the drive shaft at the same time. Yoga.

Edited February 11, 2010 by Zed Head
More #2

[IdahoKidd]

Jack stands are for kids. I actually have a rotary lift in my garage;) The PITA part is that I don't have a right shoulder rotator cuff so lifting anything much above my knees isn't much fun. BTW, with a friend to help with the lifting, I can have the tranny in and out in less than an hour. (three Z's makes for lots of practice). It is waiting for an unsuspecting friend to show up that is the hassle.

The slave moves that arm about an inch when the pedal is depressed. I'd have thought that was enough. I actually built a longer rod for the slave as I could push the piston in about 3/8 of an inch. I figured more throw would release the pressure plate. No change. As mentioned, changing the slave and the master didn't help either.

It is the 225 clutch. Not sure why that would matter except for the amount of pressure on the disc I guess.

I am pretty sure there is something amiss with the pressure plate. I can't drive the car after next thursday for 3 months nor can I fix it til then either (surgery on the shoulder). Had hoped to get to it tonight but no such luck.

[Zed Head]

I don't think that a longer rod gives you more throw. Piston movement determines throw. A longer rod might actually use up some throw by preloading or setting a short starting position for the slave cylinder piston.

Might be that you just need to bleed the system, with the original rod, adjusted to the proper amount of play. Air bubbles in the system would use up throw (piston travel) and cause your symptoms.

I think the clutch is very easy to bleed, compared to the brakes.

Just some thoughts, as to how I understand the hydraulic clutch system. Anyway, good luck.

[Nigel1943]

Jack stands are for kids. I actually have a rotary lift in my garage;) The PITA part is that I don't have a right shoulder rotator cuff so lifting anything much above my knees isn't much fun. BTW, with a friend to help with the lifting, I can have the tranny in and out in less than an hour. (three Z's makes for lots of practice). It is waiting for an unsuspecting friend to show up that is the hassle.

The slave moves that arm about an inch when the pedal is depressed. I'd have thought that was enough. I actually built a longer rod for the slave as I could push the piston in about 3/8 of an inch. I figured more throw would release the pressure plate. No change. As mentioned, changing the slave and the master didn't help either.

It is the 225 clutch. Not sure why that would matter except for the amount of pressure on the disc I guess.

I am pretty sure there is something amiss with the pressure plate. I can't drive the car after next thursday for 3 months nor can I fix it til then either (surgery on the shoulder). Had hoped to get to it tonight but no such luck.

Check out thread posted by louisf on 5-17-2007, "why is 77 4 speed collar longer than 5 speed"

[IdahoKidd]

Zed, the longer rod will only work because there is some room in the slave for the piston to move back about a half inch. That half inch isn't being used right now and I would think I would gain that extra travel. I already have the piece made and will try it before dropping it all out.

Nigel, thanks for the lead. His problem is the exact opposite of the problem I have but much of the info is very relivent. I don't know which collar came with which clutch so it may be that I will have to set down and do some math to find the correct one. The catch in all of this is that it was working well for a while. I am confident/certain it isn't in the hydraulics. I think I am going to order a complete and known matching set and start again once the doc says I can move that shoulder. I am going to have to take it all apart either way it looks like. And, I probably should follow my own advice to my clients as a contractor... "which is cheaper, doing it right the first time or doing it over again?"