Which master cylinder?

[evilmiata]

Short version: I need the bores, exterior dimensions, pictures, etc of master cylinders.

My clutch experiment didn't work. I hoped that a stock Miata master cylinder would motivate a Camaro slave. While I get slave motion when pushing the clutch, its not enough to free up the clutch plate or break the plastic retaining strap around the piston. I've done a little research:

Bore area, assuming a circular piston, is
(D/2)(D/2)(22/7) I don't know a better way to write Area=Pi 'R' squared.

Miata/X is the amount of travel the slave will travel if pumped with the same amount of fluid needed to push a Miata slave 1".

Slave cylinder`````bore``bore area``Miata/X
F-body 3.4/5.7```````1"````.786"````.562"
Fiero 2.8````````15/16"````.691"````.691"
Miata 1.6``````````3/4"````.442"```````1"

(Sorry about the ```. The forum deletes my extra spaces)

So it looks like my Miata master is only 1/2 as efficient vs. the F-body slave.

The only info I can get about master cylinders is that the Fiero uses a 7/10" bore and has a .385" bore area. I'm considering the fiero master since it looks to be a similar size to the Miata. The F-body master is too large to fit without serious firewall/wheel well modification.

Assuming that a Fiero master stroked 1" displaces .385"cu.in. of fluid, that fluid would move the Fiero slave .557". The same master would move the F-body slave .490". Thats only .067" difference, or just over 1/16".

Do you think its safe to try this clutch master with a 1/16" or 6.7% deficiency?

I also see that a '90 cavalier has a 1 1/4" bore slave and a reasonable-looking master cylinder. While I can't find the bore on this one, it could have potential if someone can get me info/pics.

[Quinky]

What are you doing? whats the application? Are you positive all the air is out of the system? How much free play is there on the throw out beering?

[evilmiata]

3.4 RWD engine and drivetrain into a Miata. I don't know how much play is in the throw out bearing. I imagine there isn't any since I can't pull the fork (or what I can grab) back. I *think* all the air is out. I lifted the master cylinder so there were no high spots in the line and pumped the slave until I couldn't see anymore bubbles. Who the heck thought of designing a slave without a bleeder?

[Quinky]

It's becoming more commen on newier vehicals..

To properly bleed that system remove the slave from the transmission.. with the cap off the master have it 1/2 - 3/4 full..
Have someone very slowly push the slave in.. if bubbles come out be ready to poor a little bit of extra fluid in the master while your friend alowes the slave to extend back out... repeat this untill you see no more air.. After that replace the cap, pump the master a few times and see if things have improved..

Having no play the throw out bearing is a good sign.. you shouldn't have any with a hydrolic system.. generaly with a hydrolic system the throw out bearing rides lightly on the pressure plate at all times.. the only free play you will feel is going to be between the push rod going into the back of the master.. and there should be a slight bit.. about an 1/8" when pushing the clutch peddle down..

the overall bore area doesn't matter with your master.. What counts is the size of the piston and how far it travels.. You have to becarefull though.. you don't want something that'll go to far and push the piston in the slave right out..

[evilmiata]

Quinky,
I already bled the system as you described. I said I "think" because I don't trust or like the Mickey Mouse clutch design. Furthermore, I doubt newer cars are coming out with bleeder-less slaves. Take, for example, our very own 3.4 Camaro. It shares the same clutch system with the 5.7l. In '96, GM upgraded to a 3.8l and a bleeder slave. In '98, the 5.7l received a bleeder.

You're on the right track with the master cylinder. What really counts is master displacement vs. slave displacement, so bore and stroke count. Obviously, my stock master is out of juice. I want a master cylinder designed to move a slave similar to the Camaro. I don't want to use the Camaro because of its length. My stock master isn't more than 4 inches long and is pretty well nestled between the firewall and the wheel well. That's why I'm looking for bores and exterior dimensions.

[hamondale]

Re: Which master cylinder?

[quote="evilmiata"]I hoped that a stock Miata master cylinder would motivate a Camaro slave.

This might be a long shot, but one way might be to have your Miata MC bored out to accept a larger piston if there is enough meat there to bore. Then maybe fit the piston from one of the larger ones. There is a company out there, Sierra Specialty at http://www.brakecylinder.com/ that bores out and resleeves MCs. No reason why they couldn't bore to an oversize if the cylinder wall was thick enough. They did my brake MC for my Sprite and it was excellent. Everybody else on another forum I'm on also swears by them. This may require some additional engineering to make or modify a piston to work, but from what I've seen of your web site, you're certainly up to it. Maybe Sierra does that as well.

[Quinky]

Some modles are coming out stock with out bleeders.. even some of the crappier aftermarket stuff doesn't have bleeder screws.. A stock Jbody slave doesn't have a bleeder screw and depending on the aftermarket one you get it may or may not have a bleeder screw.. Auto makers are getting really stupid these days with there designs..

Hamondale has a point with having your master bored out to accept a larger piston.. that might be an idea.. I am not sure if a miata master is plastic or aluminum though.. you'd have to watch out for that..

Another thing..to check is just make sure you have the right amount of free play at the clutch peddle..

maybe look at an rx7 master.. or just a different mazda masters..see if you can rig up a different combination..

[hamondale]

[quote="Quinky"] I am not sure if a miata master is plastic or aluminum though.. quote]
I didn't know anybody made MCs in something other than cast iron. Mine has plastic reservoir like lots of others but is CI. The company I mentioned, Sierra, puts a brass sleeve into the bore, more resistant to pitting from corrosion when a little water gets into the fluid. If there are MCs of aluminum, I'm not sure that's compatible with brass.

[evilmiata]

Hamondale, I'm glad you posted! Just 20 minutes ago I thought "hey, I'll bore out a Fiero master!" Its probably short enough to fit between the firewall and the wheel well. I'll have to check out yoru link. Thanks!

Quinky, I'm investigating other Mazda parts as well. Unfortunately, its tough and tedious to uncover bore and stroke specs.

[Quinky]

Most newer MC are either plastic or aluminum...

second gen J body has a plastic MC..

[RidgeRunner]

second gen J body has a plastic MC..

Sure about that? I'm pretty sure mine's aluminium.

[Quinky]

My 90 is plastic... and I don't recall changing a 2nd gen that wasn't..

The last 2 rangers we had in my shop were both plastic..