Okay, took me a while but I got it together. As mentioned earlier I did the clutch adjustment today. Itís a huge improvement, and I made sure there wouldnít be any issues with insufficient disengagement or re-engagement of the clutch. Also, I formulated a theory as to whatís causing the problems.
Make sure you fully read the instructions and study the pictures and diagrams to ensure you fully understand the process before starting.
Please note: I put these directions together based on my personal experiences. I am not a mechanic and do not have any professional certification. If you try this, you do so at your own risk and release me from any liability, damage, injury, etc. You assume all responsibility!
Hereís the How To, with some explanations and diagrams to avoid mis-adjusting the clutch:
12mm crescent (open ended) wrench
Light source (I used a head mounted light to put light where I was looking and keep both hands free)
10mm crescent wrench for clutch cylinder actuator rod (not really needed and actually very difficult to use, but just in case you want to try)
Permanent marker such as Sharpie or Staedtler
1. Turn off the engine!! Donít do this while the car is running!! Obvious but you never know.
2. Move the driverís seat all the way back to give you room to work.
3. Slide in head first on your back and get under the dashboard. Identify the clutch pedal arm stop bolt. It will look like this:
4. Mark the bolt with a dot or line at one side with the Sharpie. This will give you a reference point. When turning the bolt keep track of how many turns you did and you can easily reverse it back to original.
5. Identify the clutch cylinder piston actuator rod. Itís further up the clutch arm from the stop bolt and looks like this:
6. Mark one of the flats on the actuator rod as well. Itís tight in there so do what you can. As long as you can clearly identify your mark youíll be able to keep track of itís position. However, itís not really critical to keep track of it as youíll see later on.
7. While youíre down there, press the clutch pedal slightly while watching the actuator rod and piston (see diagram above). You should be able to feel and see some free play before the actuator rod actually starts to engage the piston. This is normal and necessary, as this means the clutch cylinder piston is fully released, ensuring the clutch is fully engaged.
8. If you want to keep the amount of free play the same, pay attention to how much it is now, so that you can duplicate it later after making the adjustments.
9. Use the 12mm wrench to loosen off both lock nuts (theyíre both 12mm)
10. Push on the clutch pedal to take tension off the stop bolt and you should be able to turn it in. Turn it in (CW) about 2 full turns to start. My final adjustment was about 2.5 turns in. Refer back to the pic of the upper stop bolt.
11. Tighten up the lock nut to set the position of the bolt.
12. Now, check the position of the clutch cylinder actuation rod. You should find that itís depressing the clutch cylinder piston in partly now. Back off the actuation rod by turning it (screw in towards the pedal). Itís still CW rotation if youíre looking at it from the firewall, but youíll be upside down looking up from the floor, so experiment.
13. Adjust the rod until itís clear off the piston, and there is a slight bit of freeplay (I set mine up with just a pubic hair of play).
14. Tighten up the locknut with the 12mm wrench. The rod will rotate a bit CW due to friction of the threads but this just increases the free play so itís okay. Compensate for it by not rotating the actuator rod quite as far as you actually wanted to, so that when you tighten the lock nut it will rotate into the desired position.
15. Eyeball your handiwork, make sure the locknuts are tight, then take it for a drive. This is important Ė test and adjust, test and adjust.
I went through 4 adjustment cycles until I was satisfied the clutch was disengaging and engaging properly while giving the best action. I was learning as I was going so it may only take you 2 or 3 cycles.
16. To test the adjustment. Stop on level ground and fully depress the clutch while in gear. Release the brake and see if there is any sense of the car creeping forward. If so, youíve adjusted the pedal too far in, so that itís not pushing the cylinder piston in far enough to fully disengage the clutch. This is not good, and youíll know because when you change gears youíll grind the syncros. Iím not sure this is actually possible with the amount of adjustment available, and I didnít experience it myself because I advanced it cautiously, but youíve been warned! If this happens, back out that stop bolt a bit!!
17. You shouldnít have any problems with making sure the clutch is fully engaged if you make sure there is some free play between the actuator rod and the piston. Unfortunately there is no easy test for this, except for maybe clutch slippage under hard acceleration or going uphill. More probably the mis-adjustment will be minor and result in premature failure of the throw out bearing, but you don't want to find out! Again take this as a big warning!
18. Repeat the above steps until youíre satisfied with the feel of the clutch, while ensuring that it fully engages and disengages.
One more time: Make sure you adjust the actuator rod so that there is a bit of free play before engaging the piston to ensure the clutch fully engages!!
Hereís a diagram of the parts in rough relation to each other:
Note that the actuator rod is above the stop bolt and only connected to the pedal arm (not below and connected to the piston, as shown in a previous diagram Ė note: it was a valuable diagram and inspired me to do this, so even if it wasnít quite correct it was still appreciated). BTW, I noticed that I put the fixing point for the spring to the car frame in the wrong spot to try to illustrate the possible spring action. Move it to the left of the pedal arm instead of to the right. Now, try visualizing what the body of the spring will do when the top of the pedal arm moves to the left. The body of the spring will "shift", introducing non-linearities.
Now, to my theory and possible clues to identify differences in clutches. Look at this following picture.
Iíve identified the big coil spring that is used to return the clutch pedal. Itís mounted to the top of the arm. The arm pivots below where the spring mounts (see diagram above). Note my spring has white paint on it. Painting springs is a standard way of identifying springs of different strengths.
I believe, from looking at the system, that the big coil spring plays a major role in the spring rate we feel at the clutch pedal. Itís an easy part to change during assembly and itís possible Mazda did a running production change due to negative feedback.
It would be interesting to get everybody to take a look up at their spring to see what color it is. If there are different colors, then it means that different rates are being used, accounting for the differing experiences. After this has been posted for a while maybe Iíll start a survey to see what color spring everybody has.
Now, hereís my analysis and hypothesis of why the clutch feels the way it did (but not anymore on my car):
After looking at the spring/pedal arm/pivot and pushing on the pedal with my hand while watching the coil spring, I came to the conclusion that due to the way the whole system of spring, spring fixing points on frame and pedal arm interacts, part of the motion is non-linear. This is due to the fact that the body of the spring will actually shift as the clutch arm moves and tries to wind it up. If there was a rod through the body of the spring this would not happen and the spring would be linear and act purely as a torsion spring, but the shifting of the body introduces a hump in the spring tension, making it non-linear in a portion of the clutch pedalís travel.
I put together three diagrams plotting spring tension vs clutch travel. This is just my guess and is based solely on conjecture. The spring rate curve is pure fabricaton based on my guess at what the spring rate might look like, but I hope it serves to convey what Iím talking about.
The first diagram shows what the stock settings look like. Note that the clutch engagement range is smack dab in the non-linear region of the curve, just where it ramps up quickly and then tapers off just as quickly.
The second diagrams show what it looks like after doing the adjustments described in the steps above. Note that by moving the pedal arm closer to the firewall itís pushed the spring into the more linear region of itís curve, and then readjusting the actuator rod to compensate moves the whole engagement range into the more linear part of the curve.
The third diagram is the one you must AVOID doing, where the stop bolt is moved in but the actuator rod has not been backed off to compensate. Youíve effectively and permanently set the clutch up as if you were ďridingĒ it, or in other words, resting your foot on the pedal so that itís partially depressing the pedal resulting in reduced clamping force on the clutch disc. DO NOT DO THIS!!
Whew, I hope this helps. This took me a while to put together, so apologies for any typos, etc, etc. Again, Iím posting this for informational purposes only, and do not make any claims as to how this may work for you. You accept all responsibility for whatever happens if you try this out.