I was replacing the clutch master cylinder on my 88 formula yesterday and I got to thinking. The clutch slave has a 15/16 boar and the clutch master has a 13/16 boar. If the master had a 15/16 boar what would be the pro's and con's? Or would there be?

I entertained the thought and came up blank.


Next question. If the pro's outnumbered the con's how could the master be board out and finding the plunger that would work.

Large bore would result in a harder to press clutch, but it would take less distance to disengage.

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86 Fiero GT 4spd - L67 swap: VS cam, GenV. Needs exhaust (ETA 9/13) Build Progress
98 GTP - Some mods

Like mentioned above, increasing the master cylinder bore will increase pedal effort, but reduce travel. Increasing the slave cylinder bore will have the opposite effect (less pedal effort, but more travel).

Instead of boring out the master cylinder, you could swap in a slave cylinder from a Muncie 4-speed or Isuzu 5-speed. They both have a smaller bore than the Getrag slave cylinder, which will have the same effect as boring out the master cylinder.

Might i add to that , on that slave use Rodneys dual o-ring piston.!!! didnt think it would make that much of a diffrence but boy was i wrong!!! I swapped mine and mine shifts like a dream now. its worth the 14 or 15 bucks!!!

quote you could swap in a slave cylinder from a Muncie 4-speed or Isuzu 5-speed. They both have a smaller bore than the Getrag slave cylinder, which will have the same effect as boring out the master cylinder.

Perfect except they have different mounting requirements. Larry

quote Originally posted by trotterlg: Perfect except they have different mounting requirements.

It's an easy mod. I've done it. All you need to do is unscrew the threaded studs from the slave cylinder, then drill out the holes to fit over the studs on the Getrag slave cylinder bracket. Then it's ready to install.

I didn't like the increased pedal effort, so I went back to the Getrag slave. But like they say, whatever floats your boat.

[This message has been edited by Blacktree (edited 08-27-2013).]

quote Originally posted by ironhead.76: I was replacing the clutch master cylinder on my 88 formula yesterday...

I just finished replacing the clutch on my recently acquired '88 Formula. Clutch performance (including disengagement) is now perfect.

Perhaps there's something in my thread Here that might be of some assistance to you.

I've had clutch disengagement problems with other Fieros I've owned, so I know how frustrating it can be.

[This message has been edited by Patrick (edited 08-27-2013).]

I can see a nil increase in the clutch effort. The travel is the thought. Would the travel be drastic? I can see that being a con. It would reduce shift time. And also could a booster be fabbed? This is all for conversion. I have no clutch issues just curious what others thoughts are.

Too much travel will bottom the piston against the end of the bore. Ideally the piston should be at a resting position in the slave bore so that at disk extremes of new and worn out, the piston doesn't bottom out in either end of the slave.