Recommend me a Clutch Master Cylinder

I've done some research and read a few things, but I still ain't coming up with quite the answer I need. What options are there for clutch master cylinders that will fit in a 1995 Civic, but move the correct volume of fluid to actuate the common GM transmission input shaft mounted slave cylinder? It was in pickups to cars. I want to say your late 90s to early 2k fbody's used them, too. Is there an inline piece that has a stepped cylinder bore and piston to double the fluid volume movement? The Honda is fairly restrictive on space in that area. I'll either end up modifying the strut tower to keep the pedal assembly where it is or come through the firewall and have to modify pedal assembly. I think the Honda pedal setup offers plenty of stroke without modification. Omni does have a 3/4 bore for the civic, but even the f-body guys complain they aren't enough. 

What do you mean by "aren't enough"?

 Not moving enough fluid or too much pedal pressure? I use 3/4" bore masters in cars with aftermarket hydraulic throwout bearing units. A 2001 Camaro with a Manual uses a 3/4" bore master.

Larger bore means more pedal effort. Smaller bore = less effort at the cost of moving less fluid. If the the bearing is shimmed correctly you shouldn't need a large bore master
 

Remember trigonometry from school?  The unit circle?  You have to have a passing familiarity to get good clutch actuation.  It's more than just bore diameters and fluid motion.

Like, if the pushrod/pedal pivot angle is too far away from a right angle at either end of the stroke, you are wasting pedal travel.  This can also be used to advantage if, say, you have a old style clutch that is very stiff when fully disengaged, you can make the travel start out closer to a right angle so you get more mechanical advantage at the end of travel when the pedal arc makes the pushrod go more "up" than "out" for the same motion.  You do lose some throwout travel the more you do this.

YES ITS FIDDLY he grumbled after having to redo a hydraulic conversion three times before the pedal feel was acceptable

In reply to Trent :

Not enough as in the Civic CMC doesn't move the volume of fluid needed to disengage the clutch. I'm adjusted as far out with the clevis as I feel comfortable. Otherwise, the Civic pedal assembly is unchanged. Honda used a 5/8" bore CMC. 

Isn't the shimming needed when mixing and matching aftermarket flywheels and clutches? Or when you reface a flywheel to make up the difference? I'm fairly sure the Luk RepSet and Luk slave were for a '01 Camaro when I ordered them off of Rock Auto. 

I've put an L92 into the Civic. Bolted it up to an AR5 using Fabbot's kit and a 4L60 bell housing. The kit came with a plate to move the slave out about 3/8 of an inch. So, it should be exactly where it needs to be. 

Not sure if it will help you or not, but my RX-7 originally came with a 5/8" clutch master. Back in the '90's I swapped an sbc into the car, also swapped in a hydraulic throw-out bearing.

I've got 5/8", 3/4", 13/16", and 7/8" Wilwood master cyls on hand. I enlarged the hole in the RX-7's firewall so that the Wilwood's could mount flush against the firewall, also re-threaded the RX-7's clevis to fit the Wilwood pushrods. After trying them all, the 13/16" master is where I settled for a conventional 10.5" single disc dual friction diaphragm clutch.

Grant

Wow, 13/16"?  It's amazing how much more fluid travel is needed for those clutch hydraulics.

Here's a close-up of the PN# 260-5920 Wilwood 13/16" master, it's fairly small...

Grant

minstmeat said:

In reply to Trent :

 

Isn't the shimming needed when mixing and matching aftermarket flywheels and clutches? Or when you reface a flywheel to make up the difference? I'm fairly sure the Luk RepSet and Luk slave were for a '01 Camaro when I ordered them off of Rock Auto. 

 

I typically install the Tilton 6000 series in Tremec transmissions (TKO, T56, ect) but have used aftermarket replacement throwouts from the parts store. The instructions state to shim the unit so that the bearing is around 0.120" from the pressure plate contact point on installation. I have never not had to shim one.

If you have more clearance than specified, you will waste a lot of pedal stroke just getting the bearing to the pressure plate and it will seem like you need to move more fluid.

That *might* be your issue. If you have a 5/8" currently a step to 3/4" would probably be wise.

hard to diagnose over the internet.

weedburner said:

Not sure if it will help you or not, but my RX-7 originally came with a 5/8" clutch master. Back in the '90's I swapped an sbc into the car, also swapped in a hydraulic throw-out bearing.

I've got 5/8", 3/4", 13/16", and 7/8" Wilwood master cyls on hand. I enlarged the hole in the RX-7's firewall so that the Wilwood's could mount flush against the firewall, also re-threaded the RX-7's clevis to fit the Wilwood pushrods. After trying them all, the 13/16" master is where I settled for a conventional 10.5" single disc dual friction diaphragm clutch. 

Thanks Grant. That's where I figured I might end up landing. You were able to stay with Mazdas pedal assembly without modifying any of the geometry? So your "stroke" was unchanged? Beautiful car. 

I should have checked that clearance when I assembled them. I watched a tick or wildwood video about the shimming. I figured since I was replacing everything new with OEM style parts that I'd be within the ballpark. The junkyard bell housing don't quite have the inspection holes a guy needs ha. 

I'm getting limited to one post an hour since I'm new. Here's a couple of pictures. This is very diy backyard stuff. Might give y'all some anxiety. I've got around 6k in it with the purchase of the car. 3.2k went to the machine shop to install melling sleeves in the block. One was cracked. Pretty common on the aluminum block 6.2's, otherwise I've done everything on my own. This forum is a terrible time through the web on my cell .

Just because it's OE parts doesn't mean it fits correctly, especially when mixing and matching and going off of an assumption that the part you are using has the same dimensions as the part that they used to make the adaptors.

You may be in the ballpark but just not quite enough travel, but it does sound like you'll be needing a larger master too.  Getting the shimming wrong just means that you run out of travel hydraulically and either hit a stop, or the slave cylinder comes apart.

In reply to minstmeat :

Welcome to GRM. Love to see more pictures of this adventure once you get past the spammer guardrails. 

minstmeat said:

weedburner said:

Not sure if it will help you or not, but my RX-7 originally came with a 5/8" clutch master. Back in the '90's I swapped an sbc into the car, also swapped in a hydraulic throw-out bearing.

I've got 5/8", 3/4", 13/16", and 7/8" Wilwood master cyls on hand. I enlarged the hole in the RX-7's firewall so that the Wilwood's could mount flush against the firewall, also re-threaded the RX-7's clevis to fit the Wilwood pushrods. After trying them all, the 13/16" master is where I settled for a conventional 10.5" single disc dual friction diaphragm clutch. 

Thanks Grant. That's where I figured I might end up landing. You were able to stay with Mazdas pedal assembly without modifying any of the geometry? So your "stroke" was unchanged? Beautiful car. 

I should have checked that clearance when I assembled them. I watched a tick or wildwood video about the shimming. I figured since I was replacing everything new with OEM style parts that I'd be within the ballpark. The junkyard bell housing don't quite have the inspection holes a guy needs ha. 

Thanks for the compliment! The RX-7's pedal and pedal box is not modified at all, completely stock.

The clearance between the bearing and clutch fingers is necessary because the clutch fingers move back as the disc wears. Basically you need a little clearance, but too much un-necessarily increases the pedal travel required to dis-engage the clutch.

Grant

In reply to Pete. (l33t FS) :

Yes, I understand that. It feels like I'm 'hitting' pressure plate right after the 1" or so free play at the pedal that's still there even though it's completely adjusted out. I might try tackin' a nut on the clevis to see if I can't pop the end off of the cmc. I came across a 3/4 bore CMC that is offered by a company called OMNI. Hopefully I won't stroke it out, too. Looks like they also make the MAP sensors everyone likes to use...? At least from what I remember back when I thought DSM's were cool. 

If I quickly pop the clutch in it sorta seems like I get disengagement... So, I'm going to let this thing sit over night with the extended bleeder hose cracked level with the reservoir. I've seen a ton of people complain about how much of a PITA these can be to bleed. I slowly pumped and circulated fluid for quite a while, too. With the extended bleeder I can loop right into the reservoir. 

I'm also fighting the brakes and air in the system. So, maybe it's just me. Now I'm questioning my own abilities...   

At least I was able to get some sort of exhaust put together today. I just chopped apart what came on the car. Glued it together with some hardwire and extra mild steel tubing I'd found on Amazon for cheap. Sounds like your typical straight piped 350, but maybe even worse. Plenty of space for improvement. 

I'd like to drive it around the block a couple of times before I start nitpicking at it. I picked the car up a year ago in November. Pulled and sold the drivetrain for a few hundred while I gathered all of the junkyard parts. I slowed down quite a bit when I found out that the L92 had a cracked sleeve, but I came around finally and made my first cut into the firewall early July.