280z Auto to 5 Speed swap-- Clutch pedal height

[sboy79]

I'm back with more questions.

I installed the pedals for my auto to 5 speed swap (just swapping pedals into original pedal box). I have a 280z master cylinder and the clevis is adjusted all the way out. My pedal is sitting at about 6.5-6.75" from the floor while the manual is calling for almost 9". 

When stroking the pedal, I bottom out on the floor before I bottom out on the master cylinder.  I was told these pedals were from a 77 or 78 280z but have no way to know for sure. Any idea what might be going on here? I'm guessing maybe a wrong pedal (are clutch pedals different over the years/models?) or the wrong master cylinder. Got the master cylinder from Rock Auto and have never had problems with wrong parts before.

Any guidance would be greatly appreciated.

[sboy79]

Well, unless you guys can convince me this is a terrible idea I think I solved my problem. I added about 1/4" of length to the master cylinder rod and now I'm sitting at 8.5" pedal height. Strokes quite a bit further but still doesn't bottom out the master cylinder. I think I'll add a floor clutch pedal stop and call this good.

[Captain Obvious]

I just went through this exact same situation. Couple comments...

First, there is supposed to be a rubber bumper stop to limit the "up" position of the clutch pedal. It appears to be missing on your assembly. That bumper is important so you aren't relying on the integrity of the little retainer clip that holds the actuator rod into the master cylinder to establish the up-stop.

Second, I found the same as you that the down position was not even close to bottoming out the master cylinder, even when the pedal was all the way down. And that's good... You don't want to bottom out the master.

Third, I had three masters here, and all three had different length rods. A Luk aftermarket replacement (same as what you have) was the longest.

So for me, I adjusted the up-stop such that the clutch was the same height off the floor as the brake. It's less than 8.5 inches, but it matches my brake pedal. And between having the pedal at that height and having the push rod adjusted to it's maximum, mine lined up OK.

[sboy79]

27 minutes ago, Captain Obvious said:

First, there is supposed to be a rubber bumper stop to limit the "up" position of the clutch pedal. It appears to be missing on your assembly. That bumper is important so you aren't relying on the integrity of the little retainer clip that holds the actuator rod into the master cylinder to establish the up-stop.

I have that part, it was just not installed when I took the pic. I was talking about adding a pedal stop to the floor.  Seems wrong to just bottom out on the trim-- but maybe that's just because this car was an automatic.

Honestly your post makes me feel much better.  Both the brake and clutch are about 8.5" off the floor.  I'm guessing whatever weirdness you experienced is the exact same thing I'm seeing. Gotta be a combination of pedal boxes and pedals and/or aftermarket master cylinders.

Thanks for the feedback! I'll keep working through the rest of the swap.

[Captain Obvious]

Glad to help. And I agree, it's probably a combination of all the parts involved.

My 280 has a "down stop" rubber pad on the firewall, and I think that's a good idea. Hopefully you can figure out a relatively easy way to incorporate something like that.. 

I had one other complication aggravating my situation... I was working on an early 240, and I think my clutch pedal was bent a little. Rotated towards the brake pedal, if that makes any sense. The result of that twist was the foot pad portion of the pedal was closer to the floor than it should have been, and the hole for the clevis pin to the clutch push rod was too far from the floor. Both of those helped make my push rod "too short".

I believe that is a known issue on early 240's, but I believe they stiffened the clutch pedal significantly by the time they got to the 280.

[cgsheen1]

2 hours ago, Captain Obvious said:

... but I believe they stiffened the clutch pedal significantly by the time they got to the 280.

They certainly did and you can tell from his picture above that he has a 260/280 style clutch pedal. The 240Z clutch pedal was thinner metal and had a curve from top to bottom to give it strength. Then you can talk about the changes in the pedal boxes from series one on as the brake booster changed dimensions...

[grannyknot]

@sboy79, I hope I can jump in here for a related question, for some reason the clutch pedal of a 71/240 I'm working on is engaging right at the top of the pedal sweep.

I swapped out the new push rod for the old push rod so the pedal action would be the same as before but I'm not sure what to adjust to get the clutch to engage closer to the bottom of the sweep, open to suggestions.

Thanks

[Captain Obvious]

Granny, Are you using an older "non-auto adjusting" slave with the threaded rod, or are you using the newer self adjusting style?

Old style:

New style:

 

[Namerow]

These three photos may provide some additional insights... although they may just add to the confusion.  I have four master cylinders and two Mastervacs in my parts collection.  I've discovered that these have provided me with three different pushrod designs and three different clevis designs (although I can't say for certain whether they're all Nissan OE parts).  Mixing them up creates the potential for 9 different geometries...

 

[grannyknot]

Old style,

 

[grannyknot]

And now that I look at my own pic of the slave I think if I adjust the pivot ball backward toward the slave cylinder that should make it engage later?

[sboy79]

Granny- Pouring over old posts I think I can sum up the clutch adjustment like this. The threaded master cylinder rod is only used for adjusting pedal height. The only problem you can have with pedal height is if the pedal is too low. With a low pedal you may not have enough swing of the pedal to completely disengage the clutch making for tough shifts.
 

Clutch engagement is controlled by adjusting the slave cylinder rod and it seems the best way to adjust that is to extend the rod until you have zero free play then back it off a smidge to ensure you are not riding the clutch all the time. 
 

So how I understand it a clutch pedal engaging too low is most likely a misadjusted slave cylinder (too much free play) which could be exasperated by a low clutch pedal (not enough swing of the pedal). So basically your initial movement of the clutch pedal just takes up all the free play but doesn’t actually disengage the clutch until the free play is gone. With a pedal that sits too low by the time you’ve taken up the free play and the clutch is actually beginning to disengage you’ve run out of pedal travel to completely disengage the clutch. 
 

Air in the system acts like excessive slave cylinder free play. You have to compress the air before you start moving the fluid and disengaging the clutch. Again, too much air and you run out of pedal swing. 
 

One more possibility is failing master or slave cylinders. If the internal seals are failing you’re pushing fluid past the seals instead of moving the cylinder and, again, you run out of pedal swing to take up all the “smoosh” of the air or fluid sneaking past the seals. 
 

So to sum up:

1. Make sure you have good master/slave cylinders (not sure? Just replace them— they’re cheap)

2. Bleed the air completely!

3. Use the threaded rod on the master cylinder to set the pedal height, preferably even with the brake pedal and somewhere around 8-9” from the floor

4. Adjust the slave cylinder until there is zero free play then back it off a bit and you should be good