CNC Clutch setup leaking at master already? Less than 1K miles.

2643 Views 30 Replies 7 Participants Last post by slow-poke, Mar 7, 2014

JohnnyK

Discussion Starter · Feb 27, 2014

I was digging around under my pedals, and I felt some fluid around the MC. It's a CNC, 3/4" if I recall (And it's been about 5 years). I believe the slave to be 7/8?

This is on a T5. I am unsure of what clutch is in there (I remember it being FRPP, but beyond that, no idea). VERY hard to push down.

Anyone had a CNC brand master failure? It hasn't failed yet, but... I do not recall if I got the aluminum or the steel version. But the aluminum one would be sleeved I imagine, so is there a strength difference? (And of course, there are rebuild kits).

1000ish miles, but an extremely hard clutch pedal.. I have to dig into the clutch, one day.. Hopefully not this summer!

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22GT

· #2 · Feb 27, 2014

Strange. Sounds like a premature failure to me.

As for hard pedal, a stone-stock mechanical linkage with a roller pedal conversion is easy enough for a child to press. What sort of pedal pivot do you have?

JohnnyK

Discussion Starter · #3 · Feb 27, 2014

I put bearings in.

Something is either up with the pressure plate, or I have that FMS HD clutch.. And I remember seeing the FFRP logo when I installed the clutch.. I just don't remember which one it was. Moot point though, not digging into that yet.

Woodchuck

· #4 · Feb 27, 2014

Quite possible the M/C can't take the excess pressure needed to push the slave and blew out the seals, or maybe it's being depressed too far and bottoming out. Aluminum is probably NOT sleeved.

rbtconsultants

· #5 · Feb 28, 2014

Bartl - Can you ruin a master cylinder by pushing it too far? We have our hydraulic clutch installed but haven't driven it yet. It appears to work fine but the master definitely bottoms out before the pedal hits the floor. Should that be a concern? Is there a way to prevent that?

Thanks,

Bob

JohnnyK

Discussion Starter · #6 · Feb 28, 2014

bartl: I think it's definitely both those things in combination. So firstly, I have to figure out which clutch is in there now.

But let's assume it is the evil HD FMS clutch, and I swap to a lighter clutch. Would this leak then be inconsequential on a MC? Or would the 'damage already have been done'..

Not a big leak at the moment, mind you, I just noticed what appears to be a bit of fluid around it inside the car.

CNC, Inc. - Master Cylinder

I THINK it was this one I bought, so it says steel sleeve.

And their stainless one CNC, Inc. - Master Cylinder says "High strength design"..

But if the aluminum is sleeved, why would their be a difference in strength?

I will start a second thread about a clutch pedal stop.

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slow-poke

· #7 · Feb 28, 2014 (Edited)

I don't see how bottoming out the M/C would do any harm. The exit side of the piston has a small nub that sits in the return spring. If you fully compress the piston it simply bottoms out against the spring.

I considered removing one turn from the spring to get a wee bit more stroke.

I'm using the 3/4" CNC, no leaks so far, pedal pressure is manly but not excessive with a Motorsport King Cobra PP.

What slave are you using?

22GT

· #8 · Feb 28, 2014

Strange that it would be stiff. Are you using the assist spring? My clutch linkage is stone-stock, my clutch is BOSS 302, and it's not difficult at all.

JohnnyK

Discussion Starter · #9 · Feb 28, 2014

As I said, I have to check what clutch I'm using 22GT, but if it's the HD, there is my answer.

slow-poke: I'm using a 7/8 I believe slave.. Hopefully I'll have news on what PP I'm using.. I hope it's the HD, for the sake of eliminating the problem.

22GT

· #10 · Mar 1, 2014

JohnnyK said:
As I said, I have to check what clutch I'm using 22GT, but if it's the HD, there is my answer.

slow-poke: I'm using a 7/8 I believe slave.. Hopefully I'll have news on what PP I'm using.. I hope it's the HD, for the sake of eliminating the problem.

Do you have the assist spring installed?

Lemondrop

· #11 · Mar 1, 2014

slow-poke said:
I don't see how bottoming out the M/C would do any harm. The exit side of the piston has a small nub that sits in the return spring. If you fully compress the piston it simply bottoms out against the spring.

I considered removing one turn from the spring to get a wee bit more stroke.

I'm using the 3/4" CNC, no leaks so far, pedal pressure is manly but not excessive with a Motorsport King Cobra PP.

What slave are you using?

Quite a few stock masters will get damaged from bottoming them so I would think the aftermarket ones could also. If you stroked it all the way and then kept pushing, something has to give.

Woodchuck

· #12 · Mar 1, 2014

I guess the materials used would have a lot to do with whether it could be damaged by bottoming out. If the piston is a soft material and could be bent slightly that could certainly do it. As far as pedal effort, I didn't think about the assist spring.... what I'd be looking at first, is the relationship of the slave cylinder to the clutch release fork...the closer in to the bellhousing the less leverage and the more effort. If you can get adequate throw and have the lever point as far out as possible that would reduce effort.

JohnnyK

Discussion Starter · #13 · Mar 1, 2014

Oh yeah, that was all taken care of it when I installed it.. I guess my first plan of action before pressing the clutch anymore, is to figure out what clutch is in there, somehow.. No idea how, but somehow.

But if the aluminum master is sleeved, any reason it would be weaker? I can't see how, but... ANd nobody has had a CNC fail eh?

edit: No assist spring. Hydraulic setup.

slow-poke

· #14 · Mar 1, 2014

My experience on a 66 with a hydraulic setup is that there is a trade off between pedal pressure and obtaining enough stroke.

If the bore of the M/C is greater than the slave, you will have plenty of stroke but excessive pedal pressure.

If the bore of the M/C is less than the slave, you will have a nice pedal but not enough stroke.

Typically the master and slave share the same bore size. The clutch fork typically needs to move about 1.2", and when the M/C is mounted in the original clutch rod hole, the pedal will give about 1.2-1.4" of stroke.

Most of these cylinders are also limited to about 1.2" of travel. I have some pre-load and from what I have read its fairly common to have to pre-load the release bearing slightly to get enough stroke at the clutch end for most of the after market kits.

A M/C with slightly more stroke (about 1.5-1.7") would be better suited, but I have not found one.

95 Chevy truck slave has a 20mm bore and a healthy 2" of stroke.

If Tilton, Wilwood, CNC were to offer a M/C with more stroke, I would buy one tomorrow.

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JohnnyK

Discussion Starter · #15 · Mar 5, 2014

Problem found (but not solved). Peeked through the clutch fork hole, and saw A302 on the pressure plate.. I suppose I didn't know what "really stiff pedal" meant when I put it in. Googling it, apparently it has QUITE the stiff pedal.. So I should probably rectify this before the spring!

1bad68cat

· #16 · Mar 5, 2014 (Edited)

JohnnyK said:
Problem found (but not solved). Peeked through the clutch fork hole, and saw A302 on the pressure plate.. I suppose I didn't know what "really stiff pedal" meant when I put it in. Googling it, apparently it has QUITE the stiff pedal.. So I should probably rectify this before the spring!

I believe the A302 clutch is the King Cobra clutch from ford racing. My brother, brother-in-law and I have the same clutch in our cars, but we don't feel it's stiff by any means, although that is relative. All 3 of us have CNC masters and slaves in our cars. Just curious how the clutch master is mounted. Would you have a picture? What are you using to actuate the clutch, slave cylinder or hydraulic throwout bearing? If you mount the pushrod lower than the factory clutch rod on the pedal, that usually results in higher pedal pressure.

JohnnyK

Discussion Starter · #17 · Mar 5, 2014

I think the C302 is the King Cobra (Not sure about kit part numbers, I mean just the PN of the pressure plate).

HEAVY DUTY 10.5" CLUTCH KIT | Part Details for M-7560-E302 | Ford Racing Performance Parts

Everything I have read has people stating the HD is QUITE stiff (While the KC is not).

1bad68cat

· #18 · Mar 5, 2014

JohnnyK said:
I think the C302 is the King Cobra (Not sure about kit part numbers, I mean just the PN of the pressure plate).

HEAVY DUTY 10.5" CLUTCH KIT | Part Details for M-7560-E302 | Ford Racing Performance Parts

Everything I have read has people stating the HD is QUITE stiff (While the KC is not).

You maybe right. From what I read on Ford Racing's website it indicates that pedal effort is approximately 10% more for the HD. Not sure what that equates to pedal effort wise since it's a feel thing, but I can't see 10% blowing out seals. I'm still really curious as to the setup. Do you mind posting pictures how you mounted the master cylinder?

JohnnyK

Discussion Starter · #19 · Mar 6, 2014

I can post pics a bit later, not sure when I'll be able to get in there.

But I'm iffy on that 10%.. Some sites say the KC is 10% less effort than the HD.

But some say it's 10% less than stock, due to revised PP geometry. Either way, mine gives you a rubbery leg after a few miles in stop and go!

I CAN tell you the height of my MC is such that you can just slide a piece of paper between the Bendix booster, and the MC, with the MC being slightly LH of the pedal.

1bad68cat

· #20 · Mar 6, 2014

JohnnyK said:
Either way, mine gives you a rubbery leg after a few miles in stop and go!

I know the feeling. I use to have a clutch that was an on/off switch. Wilwood master w/ McLeod hydraulic bearing. Definitely not fun.

JohnnyK said:
I can post pics a bit later, not sure when I'll be able to get in there.

I CAN tell you the height of my MC is such that you can just slide a piece of paper between the Bendix booster, and the MC, with the MC being slightly LH of the pedal.

Back to the question at hand. So I made one bad assumption and hope I'm not making another. I reread which master cylinder you used. I had assumed you used the master CNC supplied to JMC. The next assumption I'm making is that this is installed in a 65-6. Is that correct? If so, did you use the part below with the master you bought from CNC to angle it up towards the original clutch rod hole in the pedal? I'm thinking if not, you had to drill a hole in the clutch pedal 1" lower than where the factory clutch rod goes and that would definitely increase pedal effort. The size master you chose seems to be correct for the application. My brother-in-law's clutch kit is 3/4 master, 7/8 slave (nice easy pedal) whereas my brother and I have 3/4 for both (little more feedback). Another thing is the masters can be temperamental if the pushrod travel is not parallel with the bore through the full stroke. I'll wait to see the picture(s) so I don't give bad advice.

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