Can somebody tell me the actual bore diameters of the clutch master & slave cyl? Also are they the same for the 2.8 and 2.5?

Thanks!

there were 2 designs for the clutch MC, 1st gen and 2nd gen i belive the only differance was the location or the resivor

i belive the bores are all the same but dont quote me

as for the slave, they might be differant for each of the 4 styles of trannys

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Im Rich B!tch

AIM: ONE FAST 2M8

Here's what I have saved from a similar search about a year ago, when I was having master/slave cyl troubles. originally posted by ProudGT.

quote The bore size on the OEM 4-Speed Slave Cylinder is 20.6 Millimeters or approximately 13/16 of an Inch. The bore size on the OEM 5-Speed and 85-86 6 Cyl/4-Speed Slave Cylinders is 23.8 Millimeters or approximately 15/16 of an Inch. I have checked the bore sizes on several 4/5-Speed Aftermarket Slave Cylinders and they were the same as the OEM Slave Cylinders. The bore size on the OEM Master Cylinder is 17.8 Millimeters or approximately 7/10 of an Inch. I have checked the bore sizes on several Aftermarket Master Cylinders and some were 17.5 Millimeters or approximately 11/16 of an Inch. Edited to include 85-86 6 Cyl/4-Speed

And from member stugood:

quote slaves Isuzu (13/16 bore) Getrag(15/16 bore)

from where you least expect him--Will:

quote The Fiero master cylinder was unique to the Fiero. The master cylinder has an 11/16" bore The Isuzu slave has a 13/16" bore The Getrag slave has a 15/16" bore The Isuzu slave and Getrag slave are not externally interchangeable.

Last-but not least-from the unshakable Buddy Craigg
(refering to slave cylinders)

quote Kohburn. While it is true that the all the 4 speeds and the isuzu have a 13/16 bore and the getrag has 15/16. The slave cylinder and the mounting bracket is completely different for 84 and would require substantial modification to get the others on.

[This message has been edited by maryjane (edited 08-14-2005).]

Wow, thanks Maryjane. On Archie's website, he says that both master & slave are the same size but he doesn't say what size they are.

Fierostore only shows two masters, (old & new design) but three different salves.

Of course, the service manual doesn't mention the bore diameter of any. I'm trying to do some simple volume calculation of the swept area to see how travel of the master relates to travel in the slave.

Thanks again!

Oh yes, the math...

Assuming the master has a bore of 0.700 and the slave bore is 0.940 then my measured stroke at the master of 1.375 would only be able to produce 0.77 of movement at the slave. Past experience has shown that an inch of movement at the slave is possible (& necessary), therefore I am either not getting enough movement at the master or the slave to master bore ratios are still incorrect.

[This message has been edited by Gordo (edited 08-14-2005).]

You can use the Excel sheet in my brake upgrade article to calulate the area and ratio easily. You'll have to use decimal, not fractional inputs. (The sheet works for metric or inch just fine. Ignore the mm titles on colums) IE...

11/16=0.6875 inch.
13/16=0.8125
15/16=0.9375

I get 1.86:1 for the small slave and 1.397:1 for the bigger slave.

IF you really want to run all the numbers....

Area=Pi*R^2=0.371 sq in

Volume= area * height= .371 * 2 inches of mc travel = 0.742 qubic inches of fluid moved. (I just went with 2 for easy math. Don't know how much the MC actually moves.

All you really need tho is the ratio... That will tell you how much the slave will move for a given MC distance. The trick is accurately measuring the travel of the MC piston.

Anytime you want the bore of a MC or slave cylinder, look up the rebuild kit for the assembly in question. Those nearly always list the diameter.

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Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurasic Park)

The Ogre's Fiero Cave (It's also at the top of every forum page...)

quote Originally posted by Gordo: therefore I am either not getting enough movement at the master

you're kinda being vauge, but the first two post in this thread mights help
https://www.fiero.nl/forum/Forum2/HTML/062105.html

Thanks for the info. I already had the formulas into excel (majored in mechanical engineering in college ). But I really needed the bore diameters to complete the worksheet.

My theories…
If the measured travel of the slave equals the calculated amount based on the travel of the master then the bleeding is proper. If less, then there is still air in the system.

Also, I should be able to calculate the proper amount of travel at the master to give me the desired 1” movement at the slave.

Well if you have hte same ratio's I've got... the ratio gives you that right off. The part that's a bit_h is trying to measure the actual MC travel under there. To get an inch at the slave you'll move the MC 1.86 or 1.397 inch depending on which MC you have. (For everyone's trivia... if you put 400 pounds on the MC you get 744 and 558.8 pounds out of the slave respectively. You get additional leverage added at the trans thru the clutch arm/fork assembly.)

The easiest way may be to unhook the MC from the pedal so you can swing the pedal easily from stop to floor and measure the MC pivot motion as you go. Then you'll know that if the pedal is 1/2 way down the MC has moved X inch.

On a side line... Rodney has pedal bushings that are suposed to tighten the top of the pedal over stock type. I've never looked at the pedal up close so I don't know if they help or even matter. Obviously bad bushings won't help but I have no way to know if alternate bushings help.

Yes... If the slave isn't moving as far as it should for a given MC action, you probably have air or a leak in the system. There isn't really anything else that would cause that.