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

2644 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!

Save

21 - 31 of 31 Posts

JohnnyK

Discussion Starter · #21 · Mar 6, 2014

haha, no worries on the bad advice, I am somewhat educated, and can also ignore advice if need be.

3/4 for both? You aren't getting any advantage then? You just kind of made a clutch-cable out of fluid!

So yes, I'm using 3/4, 7/8... 1967. I made this kit myself, and I do remember making an angled shim! And I remember it being a REALLLLL pain to install underneath the booster! But I think I did use a lower clutch hole on the pedal, because either I wasn't getting enough travel, OR I didn't like the fact that if the master is angled up, it is NOT parallel through the travel, and starts to bend. I can't remember my reasoning though!

Save

rbtconsultants

· #22 · Mar 6, 2014

1bad68cat said:
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.

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.

Daze cars has a master cylinder rod and an offset rod adapter to let you install the master straight on the firewall and use the original push rod hole on the pedal. I have it. Works great.

Bob

Save

1bad68cat

· #23 · Mar 6, 2014

JohnnyK said:
3/4 for both? You aren't getting any advantage then? You just kind of made a clutch-cable out of fluid!

That's a good analogy. All the advantage is in the pedal ratio. My brother and I chose the same bore size to get a better feel and quicker clutch reaction. In-law's mustang almost feels like pushing air.

JohnnyK said:
So yes, I'm using 3/4, 7/8... 1967. I made this kit myself, and I do remember making an angled shim! And I remember it being a REALLLLL pain to install underneath the booster! But I think I did use a lower clutch hole on the pedal, because either I wasn't getting enough travel, OR I didn't like the fact that if the master is angled up, it is NOT parallel through the travel, and starts to bend. I can't remember my reasoning though!

The lower mounting hole is definitely creating the higher pedal effort by decreasing the amount of leverage you have.

I'm currently using the angled steel master CNC use to make. Now that I know it's installed in a 67 and an idea of the setup, your master is mounted similar to when I use to have the wildwood master and McLeod hydraulic throw out bearing I mentioned earlier. Forgot to mention my brother and in-law have 66 mustangs while I have a 68 cougar. On my cougar, I too had drilled a hole in the pedal 1" lower on the clutch pedal when I didn't know better.

Also, if you decide later you want more room between the master and booster, the standard steel master should give you more room.

rbtconsultants said:
Daze cars has a master cylinder rod and an offset rod adapter to let you install the master straight on the firewall and use the original push rod hole on the pedal. I have it. Works great.
Bob

This looks like a good solution since the angled masters are no longer available.

See less See more

Save

JohnnyK

Discussion Starter · #24 · Mar 6, 2014

Oh, their steel cylinder is physically smaller? Had I known that, I could have raised it up when installing it!

However, looking at a picture of a 67 clutch pedal, I actually think mine is mounted in the original hole, if the original setup mounts to the little bent L tab on the LH side of the clutch pedal. If so, I'm convinced this HD pp is to blame. And also possibly a worn throwout shaft? But that I will have to check when I dig in.

Save

1bad68cat

· #25 · Mar 6, 2014

JohnnyK said:
Oh, their steel cylinder is physically smaller? Had I known that, I could have raised it up when installing it!

I believe the steel version is 1" in diameter and the aluminum version is 1.75" but I will need to double check. I actually have both. I used the aluminum version for brakes.

Save

rbtconsultants

· #26 · Mar 6, 2014

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

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

The one I installed is 1.4" stroke, 13/16 bore.

It feels like it requires more pressure than I'd like, but we haven't driven it yet so we'll see. The Slave is CNC 7/8" bore slave.

http://www.summitracing.com/parts/WIL-260-11972

Pic in my car:

See less See more

Save

slow-poke

· #27 · Mar 7, 2014

rbtconsultants said:
The one I installed is 1.4" stroke, 13/16 bore.

It feels like it requires more pressure than I'd like, but we haven't driven it yet so we'll see. The Slave is CNC 7/8" bore slave.

http://www.summitracing.com/parts/WIL-260-11972

I'm surprised that M/C will provide enough volume to fully disengage the clutch.

Save

rbtconsultants

· #28 · Mar 7, 2014

slow-poke said:
rbtconsultants said:

The one I installed is 1.4" stroke, 13/16 bore.

It feels like it requires more pressure than I'd like, but we haven't driven it yet so we'll see. The Slave is CNC 7/8" bore slave.

http://www.summitracing.com/parts/WIL-260-11972

I'm surprised that M/C will provide enough volume to fully disengage the clutch.[/QUOTE

Why? The daze mc is 3/4" bore, and I don't think it's stroke is as long either.. Math says I get like 1.3"+ stroke at slave, which seems plenty to me. I'll measure on Saturday.

Bob

Click to expand...

Save

slow-poke

· #29 · Mar 7, 2014 (Edited)

A 13/16" master and a 7/8" slave gives a ratio of 0.93, stroke @ M/C = 1.4", stroke @ slave = 1.3"

I'm using a 3/4" Master and a 20mm slave (ratio = 0.95), stroke @ M/C = 1.55", stroke @ slave = 1.4"

With 0.95 and fully bled I have enough stroke (but just enough), works and feels great, however at the drag strip with RPM >6000 the car wants to creep forward.

My M/C is mounted on an angled spacer (outlet side down a few degrees), so if any air gets in the system, the air gravitates to the top and reduces stroke.

When I bled the system I had to put the front on tall jack stands to get all the air out.

If I could find a M/C with say 1.7" of stroke I could do away with the angled spacer.

See less See more

Save

rbtconsultants

· #30 · Mar 7, 2014

Do you have any preload on your clutch fork? my understanding is 1.4" stroke at the slave should be more than enough. Sounds like you have way more experience than me, so I'm relying on what I have researched. I bled with a pressure bleeder from the slave up.

Bob

Save

slow-poke

· #31 · Mar 7, 2014

rbtconsultants said:
Do you have any preload on your clutch fork? my understanding is 1.4" stroke at the slave should be more than enough. Sounds like you have way more experience than me, so I'm relying on what I have researched. I bled with a pressure bleeder from the slave up.

Bob

Yes, some pre-load, I'm using a King Cobra diaphragm style pressure plate.

You might be fine with 1.3" at the slave, I only experience the creeping issue at pretty high rpm, anything under 5000rpm works perfect.

Save

21 - 31 of 31 Posts

This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.

Top Contributors this Month