fl327 Posted January 13, 2004 Share Posted January 13, 2004 I posted a while back about using the 240sx rear brake line as a clutch hose, works good, used a goodridge line off one of my sets of rear calipers. I initially didnt bleed the clutch very well, looking back the line had air in it for months, causing my pedal settings to be inaccurate. Once I finally bled the thing right, three clutch pumps and puke---overextended the pushrod. Got my spare oem out, adjusted pedal back down to stock height- "crunchy" clutch engagement. Begin to adjust pedal higher, and I find that either it is very hard to go into gear from a stop or that when it is shifting nicely from a stop, sooner or later I blow out the slave cylinder pushrod? Finally I get really upset, jump in my other car and rush the junkyards- taking every rwd nissan slave cylinder I can find. There was a 280z there so I would grab two or three of them, and bolt them up to the z tranny to check fit- 84-89 non turbo 300zx use identical slave to 70-8zcar 3/4 bore, grabbed three of those for backups, one of them was brand new! Maxima with L6 same thing. I grabbed two oddball slave cylinders from a 200sx, 11/16 bore, or .64 I did some math to calculate how much more throw I would get out of the smaller bore slave. Just about every rwd nissan/dats slave cylinder I pulled bolted straight up to the z tranny, I was happier than a clam about that one! 3/4=stock 11/16-200sx .64/.75 and I got .850 I am wondering if this means that the 11/16 slave cylinder will have 15% more throw at the same pedal height assuming the mc is still stock bore? I installed the 11/16 slave in car and put pedal back down to stock height and freeplay, and it engages a little crunchy from a stop, but goes into gear where the 3/4 setup would not go into gear. Im scared of throwing another pushrod on the floor and just want to see if Im doing this right, kinda bugs me I guess. Pedal stiffness went up a little, but way lighter than a puck clutch still. With the tiniest bit of adjustment to this slave I think I will finally have the pedal im looking for, a nice engagement close to the floor but not on the floor, and a little firmer pedal. Clutch is SPEC 240mm turbo stage 2 kevlar disk with a heavy duty pressure plate, an extremely light pedal feel so far but its holding up fine, when installed I changed pilot bearing, clutch fork, and used a new 2+2 throwout bearing mounting hub so I left these out of the equation for the weird engagement. I did a search on mechanical advantage and slave cylinder and couldnt find relevant results, so Im wondering if any of the autox gurus knew the equation so I can put together a worryfree, slave cylinder friendly, clutch setup. ****update*** bled clutch again, didnt need to but hey. raised pedal 1.1mm and adjusted freeplay, and took it for a spin. I made sure to shift as many times as possible under load, if the pushrod was going to fly out I made sure to do it close to home, and we're good! Both times the two stock bore slaves went out it was after a ride like I just took, where I get on and off the gas and try shifting it underload and from a stop, pumping the living begeezus out of the pedal. Made sure to put some load on it Pedal pressure is slightly stiffer than stock, pedal engages like stock, and best of all, it shifts nice and smooth both rolling and stationary. slave cylinder is a 1984 200sx na 11/16. Got it from the jy, after a few more days of testing im gonna get a new one. HAPPY! Quote Link to comment Share on other sites More sharing options...
blueovalz Posted January 13, 2004 Share Posted January 13, 2004 Your rational of comparing the bores is correct. The first thing I noticed as I read your post was that one SC would work in disengaging the clutch, and the other did not with only 15% stroke difference. I would think that a 15% difference in stroke would not be a factor here unless the smaller SC was just barely small enough (meaning a smaller one may be more desirable). If both SCs were correctly bled and operating well, then I'd consider a move to perhaps a 5/8" bore SC being it seems that pedal pressure is still "light" as you say. Or a slightly larger MC bore, either way will provide a longer stroke, but firmer pedal. Anyway, the total mechanical advantage is a compilation of pedal leverage X hydraulic leverage (MC bore/SC bore) X the throw-out bearing arm leverage. Then, as you said, you also must include the pressure plate leverage as well. Quote Link to comment Share on other sites More sharing options...
fl327 Posted January 13, 2004 Author Share Posted January 13, 2004 thanx, yeah I would like the pedal a little firmer. Couldnt find a sc smaller than 11/16 out of the cars, I will try the trucks next maybe ill luck out. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted January 13, 2004 Share Posted January 13, 2004 One thing to keep in mind is the possibility of damaging the fork. I've seen a few split at the ball pivot with heavier pressure plates. I would think that having more throw would make this failure more likely. Jon Quote Link to comment Share on other sites More sharing options...
blueovalz Posted January 13, 2004 Share Posted January 13, 2004 One thing to keep in mind is the possibility of damaging the fork. I've seen a few split at the ball pivot with heavier pressure plates. I would think that having more throw would make this failure more likely. True. Some styles of PP increase pedal pressure the further they are engaged, and some maintain a linear pressure, and some have a centrifugal assist. For the most part, I believe that the pressure plate pressure is the sole factor in this regards, and that this stress on the fork is the same, regardless of the mechanical advantages (or disadvantages) upstream in the clutch system. Know the characteristics of your PP will help in this regard. Quote Link to comment Share on other sites More sharing options...
fl327 Posted January 13, 2004 Author Share Posted January 13, 2004 couldnt find any info on pp online, i just drove the car around this morning to feel it out. Pedal is only marginally stiffer, before it felt like air, now it feels like a clutch-if that makes any sense. Basically pedal isnt dramatically getting stiffer, which I dont know if that is good or not, but I do know at same pedal height the smaller sc is better at engaging and disengaging clutch. Clutch and pp are rated for 450ft/lbs, yes im pretty optimistic It feels like a stock clutch basically. I am going to raise the pedal 1mm at a time until it feels right. Shouldnt be too much higher its already pretty good. Quote Link to comment Share on other sites More sharing options...
BayAreaZT Posted January 13, 2004 Share Posted January 13, 2004 I tried a pathfinder slave which is also 11/16" but after it still wouldn't disengage the clutch and blowing out the slave piston I pulled the tranny. Clutch fork was completely split at the pivot. I ended up using the stock slave for now because with the pathfinder slave I would have to use a spacer. I thought a bigger MC later on would be a better solution but if the 200sx slave bolts right up that would be an easier fix. I want to reduce my pedal height but I'm worried about how much stiffer it will get. You already know how my pedal feels. Quote Link to comment Share on other sites More sharing options...
fl327 Posted January 13, 2004 Author Share Posted January 13, 2004 Yeah, your clutch is stiff! So far the 200sx slave works well, bolts on. The stock one would work, but the pedal would be too high, and if i went lower, it would be crunchy. So far this slave is doing me david justice. Im going to adjust it again and see how it does. Its engaging right at the floor at a pedal height where the stock one wouldnt let me put it into gear, thats a good sign I think. Quote Link to comment Share on other sites More sharing options...
CU Zcar Posted January 14, 2004 Share Posted January 14, 2004 Nitpicking here, but to compare the throw of the smaller slave cylinder you'd want to use the areas of the bores rather than just the diameter. Just to show how little it matters, my math says that the new one should provide 19% more throw Guess that just makes it better for you huh? Quote Link to comment Share on other sites More sharing options...
fl327 Posted January 15, 2004 Author Share Posted January 15, 2004 Nitpicking here, but to compare the throw of the smaller slave cylinder you'd want to use the areas of the bores rather than just the diameter. Just to show how little it matters, my math says that the new one should provide 19% more throw Guess that just makes it better for you huh? Well hey thats better than the 15% I had calculated before, we'll go with yours 8) . Yes, Clutch grabs at an oem pedal height and shifts with the greatest of ease, FINALLY Quote Link to comment Share on other sites More sharing options...
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