Clutch fork throw

[rcv]

The fork is definitely on the right side of sleeve ears, between the ears and that circular retaining spring. 
 

It feels like I’ll have some throw left once the TO bearing contacts the PP springs - the fork isn’t quite bottomed out. Any way to tell if I’m going to have enough travel other than plumbing up the slave cylinder to the master and pressing on the pedal?

This is a picture of the old collar, but I installed the new one the same way. 

[rcv]

Here’s the best pic I have of the pivot ball:

 

[rcv]

I don’t think it has anything to do with the fork either. I used my old style fork with the hole in it because I’ve heard people prefer the adjustable slave cylinder. As far as I can tell, the old and new style forks have the same geometry. 
 

I think I’m going to just forge ahead with installing the engine and pray I have enough travel to actually disengage the clutch when I stomp on that pedal.  Anyone want to talk me out of that?

[Zed Head]

One last thing on your pivot ball.  Is the washer underneath it?  Without the washer it is effectively shorter which would cause some of your problem.  You'd lose the thickness of the washer plus the geometry would change slightly.

Not much else.  Shaving the flywheel would also lose you some, moving the pressure plate away from the pivot ball and throwout bearing.  

Good luck.

[rcv]

Yeah the washer is there.  The flywheel measures 27.5mm thick. As far as I know it’s never been shaved, but I can’t find any specs on what it’s supposed to be. 
 

[rcv]

Hmm looking online I found this longer looking pivot: 

https://www.datsun-garage.com/products/oem-clutch-fork-pivot-ball-1972-83-240z-260z-280z-280zx

I’ve never seen one like this, but it appears to be much longer than the one in my 4-speed (which is the same one in my 80-something 5-speed I have sitting around in the garage).

Maybe that’s worth getting and trying.  I’m getting really antsy to move this project along, but I’m sure gonna regret it if I can’t throw the clutch once everything’s in the car  

 

[Zed Head]

2 hours ago, rcv said:

I don’t think it has anything to do with the fork either. I used my old style fork with the hole in it because I’ve heard people prefer the adjustable slave cylinder. As far as I can tell, the old and new style forks have the same geometry. 

I'd use the newer fork myself.  The pressure plate and slave cylinder and throwout bearing/sleeve/collar will be designed for the newer fork.  The older fork is the one odd piece in your collection of parts.  The pivot ball looks in good shape.  The one you showed is an odd style I haven't seen before.  Might be an aftermarket part.

Plus the wear on the old fork will lose a little bit more travel.

Edited July 12, 2020 by Zed Head

[EuroDat]

I think I would remove the pressure plate and set it up on the bench with the throwout bearing collar. Start doing the math. Measure it all again. You need the 91-92mm measurement. I see you had 86mm. I'm not sure how you measured it, but if you use the same procedure you used on the old pressure plate/collar combination 91mm then something is still not right.

The clutch fork ratio is 120/65. The slave cylinder rod moves 1.85mm to 1mm throw out bearing movement. 92-86 = 6mm. 6 x1.85 = 11mm. You are measuring 135mm. 135 -11 =124. Still a long way off the 115mm bell housing to clutch fork measurement. The 115 is approximate and depends on clutch disc wear. A new clutch could be up around 118mm.

Is the flywheel surfaced. Could that be where you are loosing a couple of mm? 

If you do go ahead with the fork in the 135mm position, there is a good chance your clutch pedal will bottom out before the pedal reaches the floor and the clutch may not be fully disengaged. The other problem you will have is your slave cylinder travel will runout and pop the rubber cup out of the cylinder. You will need to make a longer rod for the slave cylinder the prevent that from happening.

 

[EuroDat]

10 hours ago, rcv said:

Hmm looking online I found this longer looking pivot: 

https://www.datsun-garage.com/products/oem-clutch-fork-pivot-ball-1972-83-240z-260z-280z-280zx

I’ve never seen one like this, but it appears to be much longer than the one in my 4-speed (which is the same one in my 80-something 5-speed I have sitting around in the garage).

Maybe that’s worth getting and trying.  I’m getting really antsy to move this project along, but I’m sure gonna regret it if I can’t throw the clutch once everything’s in the car  

 

That is not the original pivot ball. Looks like one out of the RB engined cars, Skyline R32 etc. P/N:30537-RS581

Yours should look like this. The pivot you have is correct.

Part number: 30537-21010

You should measure 26mm from shoulder to top of ball.

Btw: If you want to buy that pivot ball, you could try this to compensate for not reaching the 91mm measurement. You can use a couple of ID: 10mm washers on the pivot ball thread to extend the pivot ball. That and a spacer ring behind the thrust bearing to increase the length of the collar/throw out bearing combination. To do the thrust bearing you will need to remove the bearing and machine a ring. This is fixing symtoms, not what is causing them, but it could get you on your way.

In the last two photos are my spare fork, throwout bearing and pivot out of a 300ZX. The throw out bearing/collar measure 42mm. That would mean a pressure plate on the bench would need to be 50mm. The 300ZX plus a lot of other datsuns/nissans with the F*71A B C transmissions use the same pivot ball.

 

Edited July 12, 2020 by EuroDat

[rcv]

 

6 hours ago, EuroDat said:

I think I would remove the pressure plate and set it up on the bench with the throwout bearing collar. Start doing the math. Measure it all again. You need the 91-92mm measurement.

 

Took the pressure plate off again this morning and took a final measurement of the stack up. It looks like I’m right on 91mm from my bench to the ears.

That’s 47mm from the TO bearing/collar and 44mm from the pressure plate:

My pivot ball is right on 26mm without the washer, and ~28mm on the washer. 

I suppose it’s possible my flywheel has been dramatically thinned out, but I think it’s unlikely. 
 

So to summarize the story so far, here are the suspects in the lineup:

Unlikely Culprits:

PP/TO stack up: I measure 91mm which seems to be the consensus for the right height.

Pivot ball height: Mine seems like the standard 26mm + 2mm washer. 

Fork geometry: Both my new style and old style forks have identical geometry, which matches those from @EuroDat: 120/65

Possible Culprits:

Flywheel: Possible that it’s too thin. Mine measures 27mm from edge to edge. Anyone know what the spec is? Given the history of the car, I doubt the flywheel has ever been heavily modified.

Localized Non-Euclidean Space/Time Warping: That’s it, I’m out of ideas after this.  I really hope this isn’t my answer.

 

 

Edited July 12, 2020 by rcv

[Zed Head]

Couple more...

Is there a gap between the engine and transmission?  That will move the pivot ball back.  Picture below.

Do you get the same distance with the new fork installed?  It's a lot of work putting it all together to check, but it's the last unknown.  Maybe that older fork is deformed somehow.  It's the actual contact surfaces that matter, you can't really tell from the outer dimensions.  The pivot ball could be "sunk" in to its seat on that older fork.  The fork "tines" have a lot of wear visible.

Edited July 12, 2020 by Zed Head

[rcv]

5 minutes ago, Zed Head said:

Is there a gap between the engine and transmission? 

Hard to tell from the photo, but no there’s no gap. The bolts were torqued down to spec when I took the measurement. 
 

7 minutes ago, Zed Head said:

Do you get the same distance with the new fork installed?  It's a lot of work putting it all together to check

Heh you’re telling me. The worst part is cleaning off all the loctite from the PP bolts/holes. It’s a lot less work than getting this wrong though. 
 

I’m putting it back together now with the new style fork. The upside is that I’m getting pretty fast at this. I’ll update when I’m done.