athoose Posted June 28, 2013 Report Share Posted June 28, 2013 Seems like some people have some and some don't. Miles in service would be helpful. Quote Link to comment
datzenmike Posted June 28, 2013 Report Share Posted June 28, 2013 The 510 and 521/521 were adjustable at the slave pushrod. All others had built in play as long as the pedal had 1/16" of free play. That's travel before resistance is felt with your thumb. Quote Link to comment
athoose Posted June 28, 2013 Author Report Share Posted June 28, 2013 Thanks Mike! So the 510’s/521’s or any Datsun with an adjustable pushrod on the slave cylinder the release bearing should not be in contact with the clutch when the pedal is released. Datsuns with non adjustable slave cylinder rods will have zero clearance between the release bearing and clutch (at all times). Free play at the pedal ensures that the master cylinder is not disengaging the clutch or putting any significant pressure on the release bearing/clutch. Quote Link to comment
datzenmike Posted June 28, 2013 Report Share Posted June 28, 2013 I'll look up the amount of play on the slave push rod tonight but as long as there is some clearance, there isn't any load on the release bearing even if gently touching the PP diaphragm fingers. The adjustable ones also have a spring that pulls the clutch arm away from the clutch at rest Later ones tend to retract away from the PP when released. I'll look into it but it could simply be a spring in the master pulling the piston back which hydraulically pulls the slave and pushrod back as well. I don't know. Quote Link to comment
Silky_Johnson Posted June 28, 2013 Report Share Posted June 28, 2013 FSM says 2mm of play at the pushrod (or 1 3/4 turns of the adjuster away from the clutch fork) for early 510s. Quote Link to comment
banzai510(hainz) Posted June 28, 2013 Report Share Posted June 28, 2013 I run the 510 T/O lever on my 5speed so I can use the adjustable 510 set up(rod and threade half monn nut and Jam nut). So I know I got a good free play. Quote Link to comment
athoose Posted June 28, 2013 Author Report Share Posted June 28, 2013 Yeah my service manual just says adjust height and free play at the pedal nothing about the slave cylinder free play. Does the 510 have adjustment on the pedal/CMC as well? Checking the web yields a hotly contested debate on “air gap” (space between release bearing and clutch) vs. free play (movement of pedal before beginning clutch disengagement) on a variety of makes and models. To further complicate the issue, some mention that the bearings need to be preloaded to a degree (by being in contact with the clutch). No easy answers yet. Quote Link to comment
athoose Posted June 28, 2013 Author Report Share Posted June 28, 2013 From my 73 620 FSM Quote Link to comment
athoose Posted July 1, 2013 Author Report Share Posted July 1, 2013 So I caught this important sentence in my FSM: Play due to piston and piston rod Later ones tend to retract away from the PP when released. I'll look into it but it could simply be a spring in the master pulling the piston back which hydraulically pulls the slave and pushrod back as well. I don't know. I seemed to recall this as well, to some extent. That a hydraulic pull existed. Here is what I think happens ... When the piston it out (pedal disengaged) the reservoir is part of the system allowing fluid to enter the CMC bore, line, slave cylinder. If you push on the release lever at this point, fluid will move up into the reservoir. When the pedal/piston is pushed forward the first piston seal eliminates to reservoir from the system. It is all free play up until this moment and there is no hydraulic push on the release lever until the reservoir is cut from the system. Checking at the release lever it becomes rock solid once the piston seals out the reservoir and the system is pressurized. This is the moment when load is placed on the clutch fingers. Prior to this it's just the gravity of the fluid and the spring in the slave cylinder. In order to have the CMC keep the release bearing off the fingers (due to hydraulics) the reservoir would have to be removed from the system ....or a spring and adjustable rod would have to be added at the slave cylinder. I'm going to let the bearing ride against the fingers and see what happens. (I definitely wouldn't do this if it came with an adjustable slave) Also, if your clevis pin and clevis pin hole are badly worn you might not be adjusting out the play in the CMC(piston and rod). Especially if you stay to factory free play specs. Which may not allow complete disengagement of the clutch. Quote Link to comment
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