Stiffer clutch, Interchanging Master or Slave cylinders?

[1gentalonfan]

I have a spec stage 3 clutch(somewhere around 2200 lb pressure plate i believe), brand new master and slave cylinders, new clutch fork and pivot ball, and my pedal assembly is all tight. My clutch is still the softest clutch ive ever felt, and it has an excessive amount of pedal throw from top rest to floor. My 300zx on the other hand has a nice stiff clutch and about half the travel, and the clutch disengages way faster. My question is are there any master cylinders i can swap in (little modifying is ok) that have bigger piston bore or any slaves that have a smaller piston bore? If you understand hydraulics youd know that this would descrease the travel needed in the pedal to push the tob and pressure plate in, and also require more force to be applied to do so, exactly what i want. Thanks in advance guys.

 

[gofer]

im sure its not the clutch master/slave cylinder if you just got them and they're brand new out of the box. Im not a hydraulics expert but i did do a quick search on tuners and found this http://www.dsmtuners.com/forums/newbie-forum/328747-1g-clutch-pedal-adjustment.html

hopefully this gets you on the right track, it sounds to me like you just need to bleed it a few times and make a few adjustments to the slave cyl. and the clutch pedal engagement problems your having will be cured.

 

[1gentalonfan]

i think you misread my intentions. My clutch disengages fine right now, i just want it stiffer and to disengage faster. The way hydraulics work is the master cylinder is the smaller of the two and the slave is the bigger. When you exert say 10 lbs of pressure on the master, and it has a bore of well say 1.14 inches(thats roughly 1 square inch of surface). thats 10 pounds per square inch, now that same pressure travels through the line since fluids cant be compressed and goes to the bigger cylinder which well say has a bore of 1.8 inches (roughly 2 square inches of surface). Since you doubled the surface area the force exerted on it also doubles going from the 10 originally exerted to 20 on in this case the clutch rod. But since the slave is twice as big it also takes twice the amount of fluid to move 2 inches that the master would need to move 2 resulting in the clutch pedal needing to be moved more. What im looking to do is make it so theres more force required on the master by either making it a bigger diameter or making the slave smaller which effectively makes less travel required to disengage the clutch also.

 

[1gentalonfan]

Well I did some digging of my own through local parts stores books trying to find a car that has a bigger master cylinder or a smaller slave, with the result being that every import car i looked at from japan used a 5/8 master bore with a 3/4 slave bore which is about 15.87mm for the master and 19mm for the slave. However the domestic trucks and such used many different sizes and what i was considering doing is either to bore the master cylinder out if i can(walls may be too thin) and use a rebuild kit from say a GMC Jimmy which has a bore of 18mm, or i found a local place that can actually sleeve my slave cylinder and put a custom made smaller piston in or make the one from the master cylinder work in there. Or i have one more thing to try and thats to relocate where the clevis pin sits on the pedal assembly and see if i can move it lower (further from the pivot point) and not have it hit the sides of the master going in. I'm doubtful on that but oh well.

 

[1gentalonfan]

well I actually ended up finding a slave that almost bolts right on that was a hair smaller than stock. It's off a 3000gt vr-4. They had an 11/16th bore slave instead of the 3/4 like ours. I installed it on my car, and it makes a world of difference. Just thought i'd share the knowledge.

 

[My1GLaser]

Sweet! What did you have to do to get it to bolt up? What year is the 3k VR4? I was just looking into something like this last week. I found out that I had the wrong slave (13/16" 1g N/T) and that was causing my problem. I got a 1g AWD 3/4" and it is much better, but not perfect.

Have you measured how much your fork moves? Mine moves 16mm right now, but I would like a like more stroke if I could get it easily. Before all the stuff I did to fix it, I was only getting about 11-12mm of fork movement and I couldn't get into gear at all.

Do you have any idea how much movement is going to be too much where the PP fingers will hit the clutch disc springs? An unsprung disc shouldn't have an issue, but I am sure there is such a thing as too much fork movement.

 

[1gentalonfan]

no I haven't measured that, but I can feel in the pedal it disengages much quicker now. I dont think it'd be possible to hit the pp on the disc springs. I think the clutch fork would hit the side of the tranny first, but I pushed my all the way in and it was just normal.

As for installing, it mounts on the opposite side of the tabs as the stock one, the holes arent threaded where ours are, and the hydraulic line is on the top and not the bottom. I bought 2 same size bolts that were about 1/4 inch longer with nuts and mounted it that way. As for the line that was just a minor bend in the stock hardline to get it to line up. Also be sure to use our stock slave rod not the 3s one. The one for the 3s is a little shorter and it ends up being too short.

The years for the slave are 92-up. It HAS to be off the awd 3s though, as the fwd version is the same 3/4 bore as ours.