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. 

One thing I want to clarify.  You are adjusting the pushrod to be as short as possible while still touching the master cylinder piston, right?

If the pushrod is as long as possible, you are losing that much pedal stroke (assuming that the master cylinder has some sort of stop)

I am running a 7/8" master in my gm (3.9 v6) swapped rx8 with the gm htob.  It feels great!  I had previous run a 3/4 in my racecar with the same setup and had to adjust the pedal linkage to get more pedal travel for it to work properly.

I ised this exact master cylinder.

https://www.amazon.com/gp/aw/d/B016MXDST8?psc=1&ref=ppx_pop_mob_b_asin_title

My first LS swap way back in the day was all OE parts and still needed a hefty slave cylinder spacer to get proper disengagement. Even if you're getting a bigger MC I would pull the trans to measure and make sure you're not wasting travel.

wvumtnbkr said:

One thing I want to clarify.  You are adjusting the pushrod to be as short as possible while still touching the master cylinder piston, right?

If the pushrod is as long as possible, you are losing that much pedal stroke (assuming that the master cylinder has some sort of stop)

I am running a 7/8" master in my gm (3.9 v6) swapped rx8 with the gm htob.  It feels great!  I had previous run a 3/4 in my racecar with the same setup and had to adjust the pedal linkage to get more pedal travel for it to work properly.

For what it's worth, a friend at a Mazda dealership did some scrounging and found that ALL Mazda rear drives use the same clutch master and pedal ratios, just maybe different boltups to the firewall.  All generations of RX-7, RX-8, Miata.  So you also started with a 5/8 master.

In reply to Pete. (l33t FS) :

Interesting!

I never tried the gm htob setup with the stock master.  I wonder if I could have got it to work?

To get the 3/4 one to work, I had to drill a new hole in the clutch pedal "arm" down about 1/4 inch. (Iirc).

Also, is there a build thread for this thing? That's one of my favorite gen civics and I've always thought an LS powerplant would be fantastic.

iansane said:

Also, is there a build thread for this thing? That's one of my favorite gen civics and I've always thought an LS powerplant would be fantastic.

I don't have a build thread. Got a few pictures on my phone, but it really isn't anything special. I hacked apart the front sub-frame wide enough to fit the GM bell housing, but made sure I wasn't removing any mounting. I never even dropped the sub frame. I need to box all of it back in and re-torque the mounting bolts, still.

Then I went to town with a cut off wheel on a 4 1/2" grinder to open up the firewall. Trying to keep anything that I could. Probably cut a lot more than I needed to, but I initially was going to keep the truck intake. I ended up coming across a slightly damaged ls3 intake with fuel rail and injectors.

I stayed between the unibody 'rails' and opened up the location for the transmission. The ar5's shifter is about 2 inches forward from where the factory Honda one was positioned. After I got the transmission where I wanted it I spent some time mocking up the backend. All I've got there is just a late 80's Ranger 8.8. The carrier/center section is offset to one side on them. So, I lopped off what I had to on the long side to reuse another short axle. Did it on a rickety wood bench on jack stands. Used a cut off wheel to make both cuts, hand beveled it with the same grinder and a flap disk, and then tacked it up and tig'd it together. I also welded the axle tubes into the center section with some 309L. Not sure if it was needed, but I came across a few posts where it was recommended. I think the overall axle length axle flange face to axle flange face was 54 and some odd inches all said and done. It was about 8 inches too short, so I've got quite the adapter plate and spacer setup going on at the moment. Went around my ass to get to my elbow. That's what I get for flying with some track width number I'd assumed was close after adjusting for OE wheel offset. I did use some silicon-bronze filler to hold the spider gears together... I'd never had the chance to run the stuff, but man it's fun to braze with the ol' tig. Looks really nice, too. 

The rear axle is mounted with some S-10 triangulated 4-link kit I'd first purchased off of Maxxxpeeding Rods? Wild experience with them. I never got the full kit, not even after they'd repeatedly resent individual parts. The box looked like it was used for target practice when I got it. Someone spent more money on tape then I'd spent on the kit trying to seal it back up. I found another one of the identical kits on eBay for cheaper yet. It came complete at least. I half followed some instruction sheet for the legitimate kit that these people had copied. I'm sure it'll need some components moved or light adjustments, but it seems to go up and down without binding and keeps the pinion angle consistent throughout the range of motion that the Honda will ever see. I was actually able to mount the rear struts directly to the lower arm bracket on the axle. I modified the strut mounting slightly, but I think it'll do what it needs to for now. To make space for the axle I dropped the fuel tank and cut about half of the spare tire well out. That includes the lower control arm cross bar. I don't think it'll really matter that the stamped and spot welded in unibody cross bar is gone, but I guess I'll find that out, too. I was able to use the factory Honda brake lines. Even the rubber ones. Just got some adapters and built a couple of little jumper tubes. Nothing fancy. I'm sure I can have someone build me a braid ss line in the future.

There's a machinist here in town that has a few stacks of old driveshafts laying around. I was able to eyeball an aluminum one with the right u-joints. It's not quite long enough, but it feels solid even without the rear suspension compressed. No play in the slip yoke into the output of the transmission. I need to swing back up there and see if he has another shaft a little longer... 

The fuel system isn't anything special, either. I managed to stuff a wally 450 into the Honda's factory sending unit, but upgraded all of the in-tank wires. Which reminds me I need to build myself a fuel pump rewire kit... I just extended the Honda's fuel pump power wiring. I need to do it with the level sender, too. I plan on retaining as many of the factory gauges as possible. The tank is sittings in the trunk as of right now. It's plumbed to regulator I found on Speedway. Used some field attachable 3/8" fuel line kit from Amazon.

Up front got kinda weird. I was able to swap the front knuckles side to side. That moved the outer tie rod mounting to the front. Which also required a completely different steering rack, but I found a way to reverse the Honda one. I wouldn't recommend it, but I think it's going to be solid. I need to get my tie rod situation figured out, but I think I'm onto something now that I understand tie rod angle should be parallel to lower control arm. At least close, or you create a crazy bump steer situation. Installing the tie rod into the bottom instead of the top has put me very. I was able to flip the castle nut and grab a couple of threads. I promise I won't drive it on a public rode like this haha. 

The steering shaft needed extended. I chopped the splined section off of the steering rack and put it back into the end of the shaft where it originally was at the firewall. Bought myself a Dewalt universal joint, A couple of 1/2" ID PTO shaft bearing kits with the mounting block and wedge ring, found some old 1/2" drive extensions I never use, and melted it all together with hardwire. Doesn't look great, but I haven't been able to twist it apart yet.

The radiator was another Amazon special. 2.5x19x31 is what I believe it is. Came with fans and shroud. I converted it to a dual-pass? Inlet and outlet are on the same side and I split the tank... Seems to cool just fine idling in the garage. Don't have the fans hooked up yet, but I'll use the E38's outputs to control the Honda's relays. Should work fine... Took some more cutoff wheels to make space for it, but it fits. I've got the heater core lines looped for now, too. I'd like to have A/C and heat, but I know there ain't space for a compressor. I see that there are 12v options out there, tho. 

The exhaust manifolds are flipped sides. Built a cross over/y-pipe that comes back over the steering rack and under the starter. Kinda sloppy, but it doesn't leak. I did cut the flanges off of the nasty oem manifolds and replaced them with the more common 3-bolt style.

It was a pain to get the truck throttle body and water pump to work with the car intake manifold. I ended up slipping the truck manifold gaskets under the car manifold. It seems to seal up, and I think I found spacer plates that are meant for this exact thing. We'll see if it pans out. I'm concerned with the job the machine shop did and installing the Melling sleeves. They weren't too confident in their work... 

Sorry for the long message! I wanted a Miata, but didn't want to pay Miata prices. I think I've done worse... 

In reply to wvumtnbkr :

It is actually threaded out. You have a clevis that pins into the pedal up high. There's just one pivot point for the pedal, and it's above the clevis. The clevis threads directly onto the plunger for the master. I have the clevis backed out as far as possible. When you press the pedal in, the rod and clevis move the same direction into the CMC. If that makes sense. 

I think I understand.  I also think you want that rod as short as possible, not as long as possible.

What stops the pedal when pushed down?  Does it hit a physical stop, or the floor?  Or, does it just not go any further?  If it just seemingly doesn't go any further, it's probably bottoming out in the MC.  If it is bottoming out in the MC, then you are loosing a usable volume.

Also, if the MC piston is pushed beyond its fully retracted position, it may not be properly uncovering the ports in the MC and make it impossible to bleed.

Highly recommend if you haven't already measure your air gap on the throw out bearing and shim it as needed. T56 style shims are currently on clearance for about $3 a piece on Holley's website FYI.

I have a pretty cobbled together LS swapped Ram50, the clutch pedal and clutch feel have been the biggest pain point in that whole project.  Look into doing a remote bleeder on the slave cylinder if you haven't already. Mine is long enough I can just dunk it in the master cylinder reservoir and it makes bleeding a breeze.  After you take a look at the pedal and pedal ratio I would also look at sizing up you master.  After playing with a few sizes and a lot of pedal adjustment I've settled on a 7/8" bore AFCO master cylinder, this is the same size bore that Tick sells as an "upgrade" to F-Body and Corvette guys.

You should definitely post some photos up/start a build thread, we are a very visual crowd here and love crazy projects like yours.

In reply to minstmeat :

Sounds bitchin'. I love it.

In reply to wvumtnbkr :

Oh, are you saying I'm adjusted too far out to the point I'm actually into it the stroke already? 

I got the Omni Master installed and I get disengagement. Feels good enough for what it is. Brakes finally stiffened up after I pulled and bled the master as well. I aligned the thing with a tape after I got the car wheel dollies square with the tire. Kept it square cause I'm still getting a fair bit of toe in under compression. She is lowww.