Nissan 370Z Forum - View Single Post

turbodog · 12-20-2010, 10:00 AM

Please excuse the length of the following post.

Well, considering that there are now at LEAST 11 pages of posts on this topic, it is clear something is not as good as one might expect in a modern sports car. While I had adapted to the clutch quirks in this car, I am not one to settle for what the factory provided if I don't like it. So, I investigated and made some changes and am 100% happier. My investigation revealed 2 flaws:

1. (as others also have noted) the engagement point is too high off the floor, causing one to have to modulate at the engagement point with one's knee up in the air. Not optimum. Can it be driven this way? Sure. Would ANY race driver (not that I am) worth his/her salt NOT change it in order to improve overall performance? No.

2. The return spring on the pedal is not a simple affair. It is a linkage to a spring unit which is oriented 90 degrees away from what you might expect (for space considerations, I'm sure). The relationship between pedal motion and spring compression is not linear. It is a sinusoidal relationship. A sine function 'rate of change' (slope of curve; energy needed to move the pedal) passes through zero and 'infinity' (changing from positive to negative at each of these points) as the input (clutch pedal position) changes. This friggin linkage goes through the 'infinity' point in the relationship right about at the engagement point.

If anyone does the adjustment detailed in the other clutch thread, they can experience this first hand. With the clutch push-rod disconnected from the pedal, move the pedal through it's range of motion, starting at the pedal fully 'up' position. Push, resistance, push, resistance, push SNAP the pedal goes to the floor and stays there. You have to pull it back up (with the master cyl push-rod attached, the clutch spring, fed back thru the hydraulics, pushes the pedal back up). Pull, resistance, pull, resistance, pull SNAP the pedal snaps up to the fully 'up' position. The SNAP occurs where? Right at the stock engagement point. Maybe this was on purpose... the pedal 'helping' inexperienced drivers to get their foot off the clutch pedal once the thing is engaged.

The net result is a distinct change in pedal response, right where I least want it. What to do? Well - fortunately- when the push-rod linkage is adjusted, the relationship of pedal-position-to-engagement-point is changed, and the spring snap-over occurs well past the engagement point, as I am taking my foot off the pedal.

As discussed above, a good driver can compensate for a lot of faults in the car (Fernando Alonzo in a 2009-spec Renault F1 car comes to mind as a possible pinnacle of that!), but don't overlook the fact that many faults (such as the clutch action in our 370Z) CAN be fixed.

12-20-2010, 10:00 AM	#99 (permalink)
turbodog Base Member Join Date: Sep 2010 Location: Dallas, TX Posts: 129 Drives: 370Z Rep Power: 15	Please excuse the length of the following post. Well, considering that there are now at LEAST 11 pages of posts on this topic, it is clear something is not as good as one might expect in a modern sports car. While I had adapted to the clutch quirks in this car, I am not one to settle for what the factory provided if I don't like it. So, I investigated and made some changes and am 100% happier. My investigation revealed 2 flaws: 1. (as others also have noted) the engagement point is too high off the floor, causing one to have to modulate at the engagement point with one's knee up in the air. Not optimum. Can it be driven this way? Sure. Would ANY race driver (not that I am) worth his/her salt NOT change it in order to improve overall performance? No. 2. The return spring on the pedal is not a simple affair. It is a linkage to a spring unit which is oriented 90 degrees away from what you might expect (for space considerations, I'm sure). The relationship between pedal motion and spring compression is not linear. It is a sinusoidal relationship. A sine function 'rate of change' (slope of curve; energy needed to move the pedal) passes through zero and 'infinity' (changing from positive to negative at each of these points) as the input (clutch pedal position) changes. This friggin linkage goes through the 'infinity' point in the relationship right about at the engagement point. If anyone does the adjustment detailed in the other clutch thread, they can experience this first hand. With the clutch push-rod disconnected from the pedal, move the pedal through it's range of motion, starting at the pedal fully 'up' position. Push, resistance, push, resistance, push SNAP the pedal goes to the floor and stays there. You have to pull it back up (with the master cyl push-rod attached, the clutch spring, fed back thru the hydraulics, pushes the pedal back up). Pull, resistance, pull, resistance, pull SNAP the pedal snaps up to the fully 'up' position. The SNAP occurs where? Right at the stock engagement point. Maybe this was on purpose... the pedal 'helping' inexperienced drivers to get their foot off the clutch pedal once the thing is engaged. The net result is a distinct change in pedal response, right where I least want it. What to do? Well - fortunately- when the push-rod linkage is adjusted, the relationship of pedal-position-to-engagement-point is changed, and the spring snap-over occurs well past the engagement point, as I am taking my foot off the pedal. As discussed above, a good driver can compensate for a lot of faults in the car (Fernando Alonzo in a 2009-spec Renault F1 car comes to mind as a possible pinnacle of that!), but don't overlook the fact that many faults (such as the clutch action in our 370Z) CAN be fixed. Last edited by turbodog; 12-20-2010 at 10:06 AM.