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Clutch Master and Shackle

D danieljonesMember
I had finished setting timing and installing the wide-band O2 last night and
wanted to take the Pantera for a drive to get some baseline air-fuel mixture
readings. I'd made it to the interstate when the clutch got very stiff at
the top of it's travel (engaged, foot off the pedal). I gave it a strong push
and suddenly I had no pedal. I was maybe 20 miles from home with a
bunch of lights and stop signs along the way. 30 years ago when I was
learning to drive, my dad had the foresight to not only teach me how to
drive a manual transmission but also how to shift without using clutch.
That came in handy last night. I managed to make it home only once having
to start the car in gear at a light. They've started to install walk/no walk
lights with timers that count down to when the lights change which was nice
for timing the lights.

When I got it home, I crawled under the dash and found out what went wrong.
The previous owner had installed a CNC clutch master. It had a fair bit of
free play before any resistance was felt and I found out why. It appears
the shackle was only threaded one or two turns (threading it all the way
down would have taken up the free play) and it stripped out.

Several questions:

1. Is the CNC clutch master metric or SAE? It appears the fitting on
the hydraulic line was replaced so I wonder if that was to convert
from metric to SAE and a second 90 degree fitting added. If the fitting
on the CNC is SAE, then is the stud also SAE? Perhaps a thread
mis-match was why the shackle was only retained by a thread? If I
re-flare the line to install an original clutch master, what
fitting do I need
and what is the flare angle?

2. What is the thread size of the shackle (would be the same as the
stud on the back of the original clutch master)? I can thread a
7x100 metric bolt several turns but the threads in the shackle
appear more coarse. Perhaps the previous owner ran an SAE tap
through the shackle?

Getting the clevis back in looks like it's going to be treat.
Does anything keep the stud from rotating on the clutch master
(maybe just friction from the piston)?

Dan Jones
Original Post

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D danieljonesMember
The fact that the shackle (called a clevis in the parts book) was held by
only one thread and the clutch pedal still had to travel a couple of inches
before encountering any resistence makes me suspect the pushrod is too short.
In the parts book there are two different shackle lengths and pushrod lengths.
I've got a '74L with the effort reduction kit. It lists the length as 60mm
for the pushrod and 30mm shackle. Does anyone know if the the CNC master
comes with its own pushrod or do you re-use the existing pushrod? Also,
can I simply pull the pushrod through the boot to remove?

Thanks,
Dan Jones
D danieljonesMember
I went through the box of used parts from the previous owner and found the
original clutch master cylinder. It still had the original pushrod which
is approximately twice the length of the shackle or about 60mm (2.36").
Also there was a new much longer pushrod, approximately 3 1/2 inches.
I assume the CNC master came with a short and a long pushrod and the long
pushrod is for a Pantera without the clutch effort reduction kit.

Dan Jones
joulesjoules"Racing is Life, anything before or after is just waiting" - Steve McQueen
Dan,

We had a similar incident and roadside fix for someone on the way home from Vegas. This was a CNC M/C too and the pushrod locknut had worked loose allowing the pushrod to work itself undone. I can confirm it was metric thread, but not what size.

It's a tight fit up under there to get it all together. I actullay pulled the master cylinder away from the firewall and had someone hold the pushrod from outside while I worked under the dash.
D danieljonesMember
> I can confirm it was metric thread, but not what size.

It's an 8mm x 1.25.

> the pushrod locknut had worked loose allowing the pushrod to work itself
> undone.

I've got it back together now but have not tightened the locknut.

The CNC masters are typically provided with a short and long pushrod.
The short pushrod is for the cars equipped with a clutch effort reduction
kit and the long is for the cars without. I searched through a box of
parts provided by the previous owner and found the long pushrod. The
short pushrod is in the CNC master. The previous owner purchased the
parts from PPC, so I called them. The lady on the phone said Dennis
couldn't be disturbed but she measured the two pushrods they provide.
The long one was the same length as mine. If she measured the short
one properly at 2", it is shorter than the OEM pushrod (which I measured
at 2.36" or 600mm). With the slave pushrod at the length indicated in
the TSB's, there was a bunch a freeplay and not enough stroke to properly
disengage the clutch. By lengthening the slave pushrod, I was able to
take up enough of the pedal slack tht it's working pretty well now.
I had to go to 3.8" on the slave pushrod length. A turn shorter and
it was releasing too low and a turn longer and it would engage at the
top of the pedal stroke.

Thanks,
Dan Jones
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