Gray Vs Blue slave cylinders and cylinder bore size - 3000GT/Stealth International Message Center

Forest Gump · 11-10-2009, 01:55 PM

Looking at the search results it isn't really clear which slave cylinder has what bore. Here is what I've found.

The blue very early AWD and FWD slaves are 3/4" bore.

The later AWD slaves (part #MB670290) are 11/16" bore.

From the search results I thought that the gray slave was the better one, but it is the smaller bore.

My question is why did they reduce the bore size? The only thing I can think of is they wanted more throwout bearing travel. Since the master cylinder is going to displace the same amount of fluid no matter what slave is attached to it the slave cylinder with the smaller bore is going to move farther.

I was hoping to reduce my clutch effort and ordered an oem gray slave, but since it is 11/16" bore I do not think it will help anything.

Has anyone intentionally run the FWD slave on an AWD car? I'm concerned about clutch release and would rather have a slightly stiffer pedal than have a clutch that doesn't disengage.

soccermania688 · 11-11-2009, 11:16 AM

I have a fwd slave on my car now. I've had a disengaging problem since i put it on. I tried adjusting the pedal and couldn't get it right. But it just went out on me so i don't know if it was bad from the beginning. I will be getting the right one now though, I'll see what kind of difference it makes.

mattc28 · 11-11-2009, 03:31 PM

I have a fwd master and slave on mine... why? because i am using a fwd chassis and didnt feel like making new mounting holes for the master in the firewall. I didnt want to put the booster and all that crap on. I cut out and mounted rear strut towers and rear subframe mounts from an awd, and have all the wiring harnesses, motor, trans and everything from a vr4. Sometimes my leg is tired in traffic, but i don't have any clutch problems. Hope that helps.

Boostaddict · 11-11-2009, 07:18 PM

The blue slave is superior if you need a slightly larger clutch engagement point (race clutch). For stock-clutch cars you won't notice a real difference.

SHiVeR-91VR4 · 11-12-2009, 10:05 AM

Quote:

Originally Posted by Boostaddict

The blue slave is superior if you need a slightly larger clutch engagement point (race clutch). For stock-clutch cars you won't notice a real difference.

Exactly.

I've tried several of them, the blue does make a small difference if your clutch pedal is stiff.

The thing is though your clutch shouldn't be that stiff if everything is working correctly and you have stock cams.

In my situation I have race cams and have almost no vac at idle (so basically no clutch booster). That coupled with the rps c/c and it's a tough combination to slip, but the pedal pressure still wasn't insane.

Hell, even with the booster not working (I had a pinched line) the clutch pedal wasn't that bad...I measured it with a scale and it took ~50lbs to push it in. With the new slave it took ~45lbs of pressure. With the booster actually working it took 25lbs of pressure.

So if you have problems, FIX the booster! It will make way more of a difference.

jackhammer · 11-12-2009, 11:04 AM

Quote:

Originally Posted by SHiVeR-91VR4

So if you have problems, FIX the booster! It will make way more of a difference.

Thats what i was thinking

Forest Gump · 11-12-2009, 11:22 AM

thanks for the info guys, my booster works fine and does make a big difference.

I am just replacing the clutch and figured I'd replace the slave was I was at it. The 2900 lb RPS pressure plate is just a little heavy and anyway I can reduce that, even just a little is worth it to me.

The cylinder area increase is about 18%, but if I can only get 10% less pedal force that is still worth having imho.

Plus the blue slave cylinders cost virtually nothing, so it is worth a try. I got one from rockauto for $9.50.

I just wish I hadn't shelled out $70 getting a slave in from mitsu.

Boostaddict · 11-12-2009, 01:22 PM

Switching to a blue slave shouldn't make a noticeable difference in pedal effort. All its going to do is shorten the slave throw for the same amount of pedal travel (making it easier to modulate an on/off clutch).

Forest Gump · 11-12-2009, 01:35 PM

Quote:

Originally Posted by Boostaddict

Switching to a blue slave shouldn't make a noticeable difference in pedal effort. All its going to do is shorten the slave throw for the same amount of pedal travel (making it easier to modulate an on/off clutch).

shortening the slave throw is in effect like "gear reduction" and will make the pedal easier to push as shiver's scale test demonstrated.

By increasing the pedal travel to slave cylinder travel ratio you are increasing your mechanical advantage, just like having a longer wrench.

Boostaddict · 11-12-2009, 01:38 PM

Quote:

Originally Posted by Forest Gump

shortening the slave throw is in effect like "gear reduction" and will make the pedal easier to push as shiver's scale test demonstrated.

By increasing the pedal travel to slave cylinder travel ratio you are increasing your mechanical advantage, just like having a longer wrench.

I'm aware of the theory (I am an engineer)... I'm talking from actual experience. I installed blues on both my TT's and the effort change was unnoticeable. Race clutches are certainly easier to modulate though.