My old gal left me stranded today...

[epsark]

I had the problem twice of going out and having no clutch pedal pressure. The first time there was no obvious puddle under the slave, so I figured since I just got the car, maybe it had been on the low side I hadn't noticed. So filled the reservoir up, and bled the system with my mini-vac, great for one person. Next time, there was a puddle. So I needed to replace it. I just replaced the slave and it has worked out fine. The master shows no signs of degrading faster because of just replacing the slave. So, if you don't have the time/money/space/etc to replace the MC, I wouldn't sweat it for now. Wait until the time is right.

Eric

[Jeff G 78]

Forgive me, but I have heard that this is not a good idea.

If you replace the slave, you should replace the master as well at around the same time.

What I have heard is that the increased 'freshness' and boost in pressure on your hydraulic system, as a result of the new slave and fluid, can accelerate the wear on an already (presumably) failing master.

No personal experience to back this up -- just what I've been told by a few sources. I replaced both the master and slave cyls on my Bimmer in a similar fashion, for similar reasons (don't ask me about working on german cars, it was not a fun experience) ...

Maybe true in theory, but I've never had a MC go bad after replacing a slave. I've done it on at least six different Zs. It would be no different than saying you need to replace the brake MC after replacing calipers. Nobody does that.

[Zedyone_kenobi]

UPDATE:

I got up waay to early this morning and carefully got the slave and rubber hose off with it. Happy to report all fittings yeilded with no drama. When I laid the slave that came off the car (original to the car as far as my notes and receipts show) next to the one I purchased from courtesy, also an OEM unit, they were some interesting differences...

Here is the picture:

They are both NABCO units with Japan stamped in them. But the unit on the car has 11/16 stamped into it, and the replacement had 3/4. Making the logical jump that these are ID measurements, the replacement unit is slightly larger inside. This would mean more pedal travel and less pedal pressure from inside the car. I really do not mind this as my clutch as always been a bit particular. It always engaged in the first 1.5 inches of clutch pedal stroke. The last 7 inches really did not matter. So this larger volume may help get the pedal to use more of its stroke.

also of note, I pulled the push rod from both of the units...this is curious..

the push rod on top is the one off the car and has a nice hemisphere on the end to push the clutch lever. The new shiny cad one was with the replacement unit.

Obviously some part swapping will have to happen, as I do not think that replacement will work in its present state. More to come as it goes back together

[epsark]

The difference in length of the push rod may explain why your clutch would engage with so little travel. I remember replacing mine and ran into a similar situation. I wondered if the new one would need a parts swap. I went with the all new one and had no problems. Hopefully yours will do the same.

[Jeff G 78]

I am going from at least 25 year old memory here from when I did my slave swap, so...

From what I remember, the adjustable pushrod was replaced in production at some point in the 240Z years. The mating clutch fork has a hole to accomodate the threaded rod, so you cannot simply swap the pushrods as it will go right through the hole. You have to use the old adjustable rod.

As for the bore diameter difference, I cannot recall, but you might need the right bore to get the right pedal feel and stroke. A larger slave bore will cause the pushrod to move less than usual. Here's how the system works - You push the pedal, the pedal pushes the MC piston and fluid is pushed through the line. The larger the slave piston, the less the pushrod moves since the area of the bore is larger. The smaller the piston, the more it moves. The ranges are very small in the clutch system, so you might have an issue with travel.

[Zedyone_kenobi]

I think the this larger diameter will be the ticket for me. I would really like more pedal travel in my clutch, I think the extra 1/16" of ID will help me out tremendously. The rod is threaded so I should be able to adjust it out accordingly.

I plan on using the old threaded rod with the new slave.

[Jeff G 78]

You should be fine then.

[mlc240z]

You might also want to look at your clutch pedal pivot point. On my '71 the hole is oblong from wear, not round as it should be. Takes a little more travel than it should before actually engaging. Still works but I plan on either putting in a bushing or having it filled with a weld and re-drilling.

[Zedyone_kenobi]

I have not checked the FSM yet, but is there a rule of thumb on how to adjust the hemisphere on the pushrod that engages the clutch arm? How much slack should there be? I have mine tightened down to the point where the clutch arm gets too hard to move by hand. I was just thinking that if I tighten it down too much I would be riding the throwout bearing the whole time.

[lmcguffin]

Stephen,

According to the parts fiche the 11/16 slave (either Nabco or Tomico) was used until 6/72; then the slave was changed to 3/4. The p/n for the withdrawl arm changed at the same time, however drawings in the fiches show adjustable push rods for all the S30 model years. The slave p/n changed again in 7/75, but remained 3/4.

[Zedyone_kenobi]

So that sort of reaffirms what I thought that the slave I removed was the original one. Great bit of research LMCguffin! I have the clutch working now, I used my mityvac and bled the system thoroughly with much success. I sat back in the car and the pedal felt limp as heck right up until the last inch or so where it felt normal.

Looking at the 72 FSM I got from Xenon on line it shows the exact slave I received. One thing of note. My 71 slave cylinder has a hole for the spring to attach cast into the body of the slave, which the one I got from Courtesy does not have. Meaning they sent me the wrong part.

rock auto sells this part, which appears to be a Nabco sold under the beck/arnley name that not only has the ear tab for the spring, but has the proper pushrod, and it sells for about 20 bucks. While the courtesy part cost me over 50 with tax. DRAT.. I may have to order this one so I can have the proper slave as right now my spring is hooked to my bleeder screw.

Meanwhile....

I crawled up underneath and noticed I could move the clutch arm with my hand about 1/2 inch until it got to hard to budge. I used the double lock nut on the pushrod and tightened it up to that point. Now my pedal feels like it has some good resistance and the clutch works fine.

I just wonder if I have it adjusted too tight.

Edited April 29, 2010 by Zedyone_kenobi

[Jeff G 78]

The FSM shows how much slack the pedal should have. Be sure that the pushrod has some clearance for sure. If it's tight without pushing the pedal, you will quickly wear the throwout bearing and the clutch.