Clutch fork throw

[rcv]

I put the entire original original clutch setup back on this morning (collar, fork, pressure plate, friction disk) and my measurements are even worse!

I now measure over 140mm from the bellhousing face to the depressed fork, and have less that 10mm between the back of the fork and the back of the fork window. 
 

This means one of two things:

1) This has just always been like this, or at least as far back as anyone remembers. My father-in-law doesn’t remember having any clutch issues, but it’s possible this setup was just barely over the threshold of working. Unfortunately the clutch master seals were dust when I got the car, and it was shortly after replacing the MC that I started down this whole rebuild road so I have nothing to really compare to. 
 

2) I’m doing something deeply wrong with how I’m putting things together, and I’m making the same mistake with the new stack up as I am with the old. I don’t think there’s too much room for error here though, especially with the amount of pictures and videos I’ve been posting. Can anyone think of anything else dumb I might be doing?

 

I made a quick drawing of the dimensions to compare to @EuroDat’s. Interesting that the bell housing edge to nose tip is off by 8mm between out drawings and the bell housing to pivot is off by 13mm. I’m not sure what that means though. 

 

I’m going to try shimming they pivot and installing the new clutch/collar again this afternoon. If that works, then I’ll probably just leave it and move on with the rest of this build. 

[Zed Head]

19 minutes ago, rcv said:

Can anyone think of anything else dumb I might be doing?

 

That's a nice drawing.

Here's something dumb - you're putting the throwout bearing and sleeve on the fork backward.  ???  Don't know.

That 13 mm extra to the pivot ball is a lot.  Don't know how things ever worked originally but that could make a difference.  You might need to find one of those aftermarket adjustable pivots.  Kind of common for cars like Chevys, don't know about Datsun.

Edited July 18, 2020 by Zed Head

[rcv]

15 minutes ago, Zed Head said:

you're putting the throwout bearing and sleeve on the fork backward.

I would just love it if that were the case. Here’s some more media.

[Zed Head]

1 hour ago, rcv said:

I

I put both of the drawings together, for easy study.

I think that there are two puzzles.  How did it ever work before, and how do you make it work now.  Maybe the old setup only needs a few mm of travel.  The clutch discs really do expand when the pressure is released, maybe the old disc doesn't expand much so it released with a just few mm of fork throw.

If it were mine I'd probably just extend that pivot ball, make it work, and let the problem stew in my brain.  An answer would probably come up in a few years.

 

[Patcon]

That is a nice drawing

[Patcon]

Isn't there normally a front bearing cover inside the bell housing? and doesn't the fork ball normally thread into that? That would account for the disparity...

[rcv]

14 minutes ago, Patcon said:

doesn't the fork ball normally thread into that?

It certainly doesn’t look like there’s supposed to be an extra cover there. I’m not sure what it would fasten to, plus the hole that the pivot currently goes into is already threaded. Having two threaded holes on top of each other would be a weird design choice and would likely lead to cross threading/spreading. Remember, this is a monkey motion F4W71A transmission and I believe it’s the lack of that cover that ZedHead pointed out earlier. 

[Patcon]

7 minutes ago, rcv said:

It certainly doesn’t look like there’s supposed to be an extra cover there. I’m not sure what it would fasten to, plus the hole that the pivot currently goes into is already threaded. Having two threaded holes on top of each other would be a weird design choice and would likely lead to cross threading/spreading. Remember, this is a monkey motion F4W71A transmission and I believe it’s the lack of that cover that ZedHead pointed out earlier. 

I wasn't suggesting youre missing the plate. I was thinking the dimensions referenced in the other drawing seem to show the plate. I had forgotten this was the early 4 speed. We dont appear to know that your dimensions are incorrect. We have operated on the presumption they are...

[rcv]

Ok I reinstalled everything with two extra washers under the pivot to give it an extra ~4mm of height. After bolting everything back together (man I’m getting fast at this) the throw feels muuuch better.  I don’t quite have 115mm from the fork to the bellhousing, but I’m getting ~125mm which is good enough for me. 
 

I’m going to call this good for now and try to wrap up the rest of this build. I have plenty of other scary things to figure out so I’m confident I’ll be back soon. I’ll post an update in this thread once the engine is in just to validate that the clutch is actually working and has decent pedal feel with this solution.
 

Thanks for all the help everyone - I hope someday someone can come up with an explanation that makes sense  

 

[rcv]

@Patcon ah sorry I misunderstood. I think you’re right that the 71B has a plate that effectively raises the height of the pivot.  It’s possible that the 71A is just badly designed and always had throw problems, or that it relied on an even taller pressure plate that nobody really remembers.

Edited July 18, 2020 by rcv

[Captain Obvious]

AAAAAAAAAAA!!!!! I am not happy. This is NOT the smoking gun I was waiting for!!!

     

Seriously though. I hope it works and you can move on with the project!!

Edited July 19, 2020 by Captain Obvious

[Zed Head]

Maybe there's a different "PIN-BALL WITH DRAWAL" in the early year model and somebody replaced yours with a later one.  It would be interesting to see the difference at the part number change.  I just considered this and there it is on good old carpartsmanual.com.  Who knows.  Edit - I notice that it says "no interchange".  

http://www.carpartsmanual.com/datsun/Z-1969-1978/power-train/clutch/7

 

Edited July 19, 2020 by Zed Head