Clutch Fork Adjustment

[M_Dragan]

Hey everyone,

 

Can anyone give me a rundown of how to adjust my clutch fork throw? The transmission is a W58 pulled from a MK3 supra, I can't really find a spec for how much throw the fork should have. I'm running a wildwood 7/8 master cylinder with a new stock slave for the transmission. I don't want to overextend the clutch, so if anyone has a measurement, a place to find the measurement, or could measure their w58 fork throw that would help me a lot.

Edited March 28, 2020 by M_Dragan

[NewZed]

Hydraulic clutches are essentially self-adjusting.  The throw will depend on cylinder travel.  So it's your clutch pedal throw that will determine the hydraulic piston travel.  Anyway, it's not adjustable.  It's designed in to the system.

 

And, the transmission has nothing to do with clutch fork or clutch hydraulics.  The only thing the transmission does is provided a spot to hang the slave cylinder. 

 

Describe your other parts.  Engine, clutch, slave cylinder, etc.  You've probably done it somewhere else but it's not in this post.

[M_Dragan]

17 hours ago, NewZed said:

Hydraulic clutches are essentially self-adjusting.  The throw will depend on cylinder travel.  So it's your clutch pedal throw that will determine the hydraulic piston travel.  Anyway, it's not adjustable.  It's designed in to the system.

 

And, the transmission has nothing to do with clutch fork or clutch hydraulics.  The only thing the transmission does is provided a spot to hang the slave cylinder. 

 

Describe your other parts.  Engine, clutch, slave cylinder, etc.  You've probably done it somewhere else but it's not in this post.

My current setup is a 2JZ GE from an SC300, SC300 Exedy stock clutch kit, stock flywheel, Exedy stock clutch slave, and a 7/8 bore wilwood master cylinder. I believe the stock SC300 system calls for a 5/8 bore master cylinder, I picked up this 7/8 bore master cylinder a while back when I thought I would be installing a completely different motor/transmission combo in the car.

 

Would I need a 5/8 bore or would this 7/8 one work?

 

How does the self adjusting work? I was reading you have to adjust the throw at the clevis where the pedal connects to the master cylinder and that it affects the throw of the clutch fork.

[NewZed]

Self-adjusting just means that the hydraulic cylinder will pull enough fluid in on its backstroke to get a full stroke on the next pedal press.  So, even if you adjust the rod at the slave cylinder it will still push the same distance.

 

The ratio of your clutch pedal would need to be like that of a Supra if you wanted to compare those parts.  But, it might be easier to just find a Supra manual and see what the slave cylinder stroke is supposed to be.  Then do the math on your car to see what slave cylinder stroke you'll get with a 7/8" master.  There's no easy way without digging in to the math, unless you just put it together and measure what happens.

 

There is stuff in the manuals.  Here are some examples, from the 78 280Z FSM.  The pedal picture is probably to scale so you could take measurements and compare to a supra to see if you need the 7/8" cylinder.  If the pedals are the same, Z to Supra, then you probably want a 5/8" master.

 

I'd say, odds are good that you should run the Z parts on the Supra clutch.  They're both Japanese sports cars.  Put the 5/8" master on and forge ahead.

 

[M_Dragan]

On 3/28/2020 at 5:30 PM, NewZed said:

Hydraulic clutches are essentially self-adjusting.  The throw will depend on cylinder travel.  So it's your clutch pedal throw that will determine the hydraulic piston travel.  Anyway, it's not adjustable.  It's designed in to the system.

 

And, the transmission has nothing to do with clutch fork or clutch hydraulics.  The only thing the transmission does is provided a spot to hang the slave cylinder. 

 

Describe your other parts.  Engine, clutch, slave cylinder, etc.  You've probably done it somewhere else but it's not in this post.

I just ordered a 5/8 master for the clutch, you’re right it’s easier to just try to match it because  that linkage looks very similar to the design on the Supra. I’ll have to dig through my stash of FSMs for the 260-280z stuff. 
 

I hope it works lol, if it doesn’t I still have the 7/8 to fall back on.

[JMortensen]

FWIW I had a weird combo of a 3/4" master and a hydraulic throwout and dual disk button clutch. There were no instructions on what size master worked and it wouldn't have been for a Datsun clutch pedal assembly anyway, but there were warnings on not overextending the pressure plate springs. I modded the pedal stop to allow it to engage much farther out, then moved it one turn at a time until the clutch just disengaged and then I think went another 1/2 turn past that. You could do something similar if you're worried about it.

[seattlejester]

What NewZed says is on the spot. Just make sure the pedal is moving for the whole stroke and calculate how much the push rod is moving, not the pedal. Also bench bleed really well to save trouble. At least on the R154 it is also recommended to do a reverse bleed since the nipple sits in an odd spot, unbolt it from the transmission and manually pump the cylinder under the car to push the bubbles up to the top. 

 

JMortensen is also on the money with an adjustable clutch stop. I think you would feel the engagement point and you can adjust the pushrod to locate it towards the bottom, but you can add a stop at the bottom to prevent you from overstroking the slave.