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Ben's Z

Clutch will not disengage: Tried everything

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I have been all over on this problem.

 

1977 280Z 5 Speed L28ET swap is done.

 

Originally I tried to install this trans with the 77 throwout bearing collar, the slave cylinder would not bolt back up to the bell housing, and i was told to get a turbo throwout bearing collar.  I installed that and the clutch would still not disengage.  I bought a new MC and SC, installed and bled.  Got strong stream of fluid out at SC bleeder.  Ended up removing the trans again and found that the pilot bushing had chipped .  I removed the old bushing and installed a new one.  Clutch pilot tool slid nicely into pilot bushing.  Reinstalled transmissions today with fellow Z enthusiast.  Clutch disengaged with car on jack stands and went through gears, tires spun in the air.  I let the car down at the rear, front tires on ramps and now clutch will not disengage again!  Clutch clevis is almost adjusted all the way out and bump stop is not even touching the pedal.  I have between 1/2"-3/4" of travel on the rod at the slave cylinder. Trans was fine before swap.  Even with this travel this MC is still softer than the old MC.

 

I am at a total loss for words on this.  Why in the hell would the car go in and out of gear running in the air but not while on the ground?

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I noticed you said you just put a new pilot bushing in and afterward it did not work. Do you know what material that bushing is made of? We did a ford transmission swap witch needed a new pilot busing. When my father when to the machine shop to get it made he did not specify for the to use acinder bronze / oil light material. witch is a self lubrication busing. They made it out of brass. It worked fine on the jack stand for about a 5 min idle and a few revs until we put it on the road then it seized solid to the transmission shaft. 

Not sure if its that but worth a look. I hope i could have at least eliminated 1 thing. 

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Dom, about 3/4" I'd say. I just got out of the car. It will go into gear with the wheels off the ground, however when I press in the clutch the wheels keep moving. Grinds when I try reverse. This is a brand new exedy stage 1 clutch, new pilot bushing, new master and slave, new collar and throw out bearing and new clutch fork with clevis on mc rod adjusted all the way out.

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Check the total stack height of the clutch + collar.  Should be 92 mm to the tabs the fork touches down to the fly wheel surface.

 

Stop thinking about which "collar do I use?" and start thinking about "how do I get total stack = 92 mm"...  Every clutch out there seems to have a unique height, so there is no "right collar" just "right stack height".

 

Discussed here with pics

 

http://www.classiczcars.com/forums/engine-drivetrain-s30/49985-please-help-id-my-transmission-year-clutch-replacement-gone-sideways.html

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Check the total stack height of the clutch + collar.  Should be 92 mm to the tabs the fork touches down to the fly wheel surface.

 

Stop thinking about which "collar do I use?" and start thinking about "how do I get total stack = 92 mm"...  Every clutch out there seems to have a unique height, so there is no "right collar" just "right stack height".

 

Discussed here with pics

 

http://www.classiczcars.com/forums/engine-drivetrain-s30/49985-please-help-id-my-transmission-year-clutch-replacement-gone-sideways.html

I don't think this will be my issue.  I originally tried reusing my 280z collar and it was taller, I couldn't get the slave cylinder back on the bell housing without putting a prybar on the clutch fork to make enough room for the slave cylinder rod, thus I bought the shorter collar.  Right now I have the perfect amount of wiggle on the slave cylinder rod at rest. Any tighter and the fork would start to be engaged.

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I wouldn't leave any wiggle on the slave rod adjustment. If there is wiggle the initial part of the movement will be to just take up that slack. I would preload it just a little bit. Maybe 1/16" preload. That 1/16' wouldn't be releasing the clutch it would just be tightening up everything before it starts to actually work. 3/4" movement doesn't seem like enough movement for the slave rod to totally disengage the clutch. Either you still have air in the system or the parts aren't matched right. A smaller master cylinder used with a larger slave will cause the slave to not move as far as the master. If you use a larger master than slave, then the slave will move more.

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When you say it goes (went) into gear with the wheels in the air but not on the ground does that mean the rear wheels are stationary with the transmission in gear, engine running, and the clutch pedal on the floor?

 

It sounds like you need a longer push rod for the clutch master. The pedal needs to be all the way up when released to get the full pedal stoke. There should be a little free play in the pedal before the push rod starts moving the master. Read the FACTORY service manual. It has the adjustment procedure, correct pedal height, and free play specification. If you cannot get the pedal set per this procedure you have the wrong push rod.

 

There should not be any free play at the slave. The pressure plate pushes it back until the clutch is fully engaged. At this point the piston and seal in the master should have opened the vent hole to the reservoir and all presusre is released from the slave. A light spring and friction hold the slave piston in place and keeps the rod engaged into the piston and release fork sockets. If it gets loose it could fall out of place.

 

If the slave piston extends out of the cylinder bore when you push the clutch (pull back the boot and look) you have a short throw out bearing collar.

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When you say it goes (went) into gear with the wheels in the air but not on the ground does that mean the rear wheels are stationary with the transmission in gear, engine running, and the clutch pedal on the floor?

 

It sounds like you need a longer push rod for the clutch master. The pedal needs to be all the way up when released to get the full pedal stoke. There should be a little free play in the pedal before the push rod starts moving the master. Read the FACTORY service manual. It has the adjustment procedure, correct pedal height, and free play specification. If you cannot get the pedal set per this procedure you have the wrong push rod.

 

There should not be any free play at the slave. The pressure plate pushes it back until the clutch is fully engaged. At this point the piston and seal in the master should have opened the vent hole to the reservoir and all presusre is released from the slave. A light spring and friction hold the slave piston in place and keeps the rod engaged into the piston and release fork sockets. If it gets loose it could fall out of place.

 

If the slave piston extends out of the cylinder bore when you push the clutch (pull back the boot and look) you have a short throw out bearing collar.

My old MC worked fine before the motor swap and my new MC has the same length rod as the old one.  The later S30's do not have a return spring on the SC. My old collar was too long.

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My old MC worked fine before the motor swap and my new MC has the same length rod as the old one.  The later S30's do not have a return spring on the SC. My old collar was too long.

 

Right.So why did you replace the master if it was still good? The spring I mentioned is not a return spring, it is inside the slave and pushes the piston out toward the release arm to keep a little pressure on the rod to prevent it from falling out when the clutch is engaged.

 

You need to separate the diagnostics to the various systems involved.

 

First: Verify the clutch pedal and push rod are in good condition and adjusted correctly. Read the manual for details.

Second: Verify the hydraulic system working. Does the slave move in response to actuating the master? Does the slave stay extended if you hold the pedal down, or does it slowly return on its own?

Third: Verify the slave and release arm are in the correct position. Where is the piston when the clutch released (pedal down)? Is it half out of cylinder bore? Where is the piston when the clutch is engaged (pedal up)? Is it fully bottomed in the bore and there is still pressure on the push rod and release arm (can you move the arm by hand?)

 

It still sounds to me like you have a short collar for the throw-out bearing. Having a short collar will result in a very soft pedal and no clutch release, which is what you have described.

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Update: Still will not disengage.  I got another clutch from my supplier and did the 92mm bench test.  I put the pressure plate from the new kit on my bench. I put the collar and bearing together and put it on the clutch fingers.  It was 92mm exactly WITH THE NA 77 280Z COLLAR, NOT THE TURBO COLLAR I HAVE IN THERE AND WAS TOLD TO USE. I took my trans back out and installed the 77 collar because it gave me the 92mm.  I put it all back together and it still will not disengage.  I have no slack at the slave cylinder and I re-bled my master and slave, and got a strong stream out of the bleeder.

 

I AM ONLY GETTING 3/8" OF ROD TRAVEL AT THE SLAVE CYLINDER.  WHAT IS NORMAL?

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