Clutch Master Upgrade

Thought I would kick this off as this issue needs to be addressed and all input is welcome.
The only info I haven't found on the stock 944 Clutch MC is it's stroke. It's bore is 3/4"
I talked with Lee at Mccleod and he said that Tick Performance gets their fittings directly from him and that they use the 3/4" Wilwood for their C5 upgrade.
Also I got these #'s...
3/4" Wilwood has a 1.1" stroke moving the C5 slave .440"
13/16" Wilwood also has 1.1" stroke moving the C5 slave .500"

Lee says that a 7/8" 1.1" stroke MC would be too large for the LS1 clutch and would require too much pedal pressure.

All this leads me to believe that the 3/4" 944 MC may have shorter than the optimum stroke to move the C5 slave volume resulting in some of these swapped cars having clutch disengagement issues...

Please chime in with real world experience and knowlege and lets get this problem solved.
Also he suggested 3/4" Willwood 260-3374 (Tick Performance uses)
and as an upgrade 13/16" Willwood 260-5920 as possibly being optimal choice.
But for the 944 fitment in that area, the new ultra compact MC's are the way to go....
Wilwood 3/4" 260-10372
Wilwood 13/16" 260-10373

I have a theory...

How many people have NEW 944 clutch master cylinders installed?
Not many I bet...

If a 3/4" bore is adequate, a 20 year old hydraulic cylinder (that has been "non-functional" for X years) may not be up to moving the same as-new volume.

I can find the stroke limit of the 944 MC...
Give me ~30 minutes.

I had a new brake mc installed during the swap, but not a new clutch mc

Faster than that...

From mounting flange to end of pushrod @ relaxed piston position = 131 MM
From mounting flange to end of pushrod @ compressed piston position = 98 MM
(This is bottomed out, so actual stroke may be closer to 1.0 IN...)

A difference of 33 MM / 1.27 IN

944 MC bore and stroke are copasetic...
I say replace those ragged MCs.

What would be better wilwood or stock?

I have used both the stock Pcar clutch master as well as a Tilton 7/8. The stock units seem to work fine when new and the clutch is a stock self height adjusting type pressure plate. When using aftermarket clutches they seem to require a little more travel from the master cylinder to make easy engagement into first and reverse. If you track your car you will find the larger master will make quick gear changes more consistent with less chance of the occasional gear grind. Check out the C5 forums regarding the Tick master cylinder that solves C5 clutch engagement issues. The Tick unit is a Tilton that is modified to mount in the vette. My advice is put a 7/8 master in and leave your shifting issues behind. Oh yea the tilton will have to be modified slightly to bolt up to the stock location on the firewall,

I just found this...

"Aluminum cylinders with either a detachable or remote fill reservoirs, or a one-piece integral reservoir version, are available in three bore sizes from .625" to .750" with a full 1.4" of stroke to accommodate short pedal ratios, small brake calipers, and hydraulic clutch actuation on space limited applications."

Tom,

Is there a chance of overtravel of the C5 slave?

I am not really sure on the over travel of the slave but I am sure there is a limit not to mention over traveling the pressure plate. The 7/8" gave me just enough more travel so gear selection is easy. I have a short shift on the trans and it requires a little more pressure for gear engagement and when the clutch drags it can sometimes be a bitch getting into 1st or reverse. The 7/8 really improved the clutch actuation and drive ability.

Thanks Tom,

It helps greatly when someone has "been there" already...
It's been about 5 years since I called you. You were just starting the 968 conversion at the time.

I'm planning on using the C5 BH and slave on an LT1, so travel may (or may not) be an issue with the difference in overall clutch height / depth.

Compact Remote Combination Master Cylinder 7/8" Bore Size
#260-10374

"Wilwood’s Compact Combination Master Cylinders have been designed for limited space applications requiring the output capacity of a full size master cylinder. The ultra short 3.37”compact body provides 2.16” of additional clearance between the mounting flange and the fluid outlet. A full 1.12” of piston stroke meets or exceeds the stroke capacity of most full size cylinders. With 1/8” NPT fluid outlet port located at the top radius of the cylinder bore, reduces the chances for trapped air. The black E-Coated aluminum body resists corrosion and maintains a durable long lasting finish."

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Shorter than the 944 master, by .31 inches...

I'm having a friend do a little research today to see if there is an OEM "upgrade" (i.e. Audi, Porsche, BMW) that will be a true bolt on and not require an adapter or any modifications...I'll post anything he finds. My gut tells me there should be a 7/8 bore MC out there with the same flange.

Anything but the 3 german builders..... That's sacrilegious to a hybrider's code of ethics!

OK, we're also looking into a Studebaker retro fit as well...

Any progress on finding a direct fit 7/8" master or just replace with the factory unit?

I have used CNC products before (they're mostly roundy-round stuff):
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The bolt spacing might be a little different, but then again that might solve some of the punch-through issues people were having....

It was warm enough to go play on the beast outside. Took apart the clutch MC from the firewall....
First things first how the #$^# do you get the Fuse box out after unscrewing the 2 tabs? It feels like it is still spring loaded from underneath!
Anyways long story short.... after mocking up the 5/8" MC I had on hand, The 944 firewall studs are 8mm and 50mm C2C... The wilwood/Tiltons are 57mm C2C... What this means is the Wilwood bolt holes have plenty of meat to be slotted the 3.5mm on each side and it slips right in the 944 firewall.... no adapter required... The remote reservoir cap even clears the Tilton Dual brake setup when it is on it's side and this positions the 1/8 NPT output end of the MC for even more connection clearance... The pushrod will have to be worked out when the Willwood shows up. I will be able to confirm if the stock 944 Clutch pushrod can just be turned down on the lathe or a new longer one made from scratch.....
So good news again....The 7/8" Wilwood 260-10374 is on its way

First things first how the #$^# do you get the Fuse box out after unscrewing the 2 tabs?

There are like 500 wires (well alot anyway) under the fuse panel that are curled and if its cold out, the panel is near impossible to pull up. But no, theres nothing under there that is holding it down. When you do get it to pull up, it only comes up about 5-6 inches unless you really get it warm inside the car in which case you can get it up quite a bit.

xschop,
You will also need to mill the body of the master cylinder so the nuts will have room to clear and allow room for a socket to tighten them. The stock push rod was too short when I did mine but I can't remember by how much but no more than an inch.

Cut some zip-ties free...
Half a dozen or so hold the harness in place.

I was able to move the fuse panel completely to the outside of the mounting location, and didn't have to disconnect anything. Gained about a foot of freedom with a little "snip_snip"...

968ls1 wrote:The stock push rod was too short when I did mine but I can't remember by how much but no more than an inch.

The drawing I posted adds 25 MM to the stock length, so without the .25" plate, the pushrod drawing should be what you need, as it is adjustable by ~30 MM.

The distance from the pedal to the Tilton/Willwood master is longer than the stock unit; the stock unit extends farther into the passenger compartment. I also have a reinforcing plate on my firewall to add strength and that made my push rod longer as well.

968ls1 wrote:The distance from the pedal to the Tilton/Willwood master is longer than the stock unit; the stock unit extends farther into the passenger compartment. I also have a reinforcing plate on my firewall to add strength and that made my push rod longer as well.

How did you handle the difference?
Thanks, Gene

No Milling required....I have some low profile m8 x 1.25 nuts and an open end wrench for that.
There may be enough room to make a pushrod adapter that just screws onto the Wilwood assembled pushrod. If not the Wilwood can be disassembled and the factory rod removed.

I removed the Tilton push rod and spliced (welded) it to the factory push rod. I put a sleeve between the two peices for some overlap and welded it in place. It would probably be best to make an new one like xschop but the day I did mine I did not any bar stock to make a new one.

The full spec...

(Edit in progress...)

This should be squeaky-close, without actually mocking it up on the firewall, and without
using the firewall plate. Add the thickness of the plate if reinforcing the firewall...

Test-fit may prove a slight length adjustment, but the adjustability of ~30MM should
get it PD close.