[Fot] Spitfire Slave Cylinder Vexing Me

[Duncan Charlton]

Mike,

A friend discovered silly putty-like gunk in his brake hydraulics after using
a borrowed can of silicone fluid to refill reservoir on his brake system
(previously filled with DOT 4 -- probably very old DOT 4, at that) as a
get-it-home measure.

I assume you reused the same clutch and pressure plate, so travel of the
throwout bearing should remain the same.  Have you already checked to make
sure that you haven't used all of the available travel in the slave cylinder?
If so, lengthening the pushrod would seem to be the solution.  Is there a
spring that withdraws the throwout arm?  If it pulls back too far, some of
your pedal travel will be eaten up when taking up the slack, i.e.: when moving
the throwout bearing against the pressure plate.  If there is a spring and you
don't want to remove it (letting the bearing ride against the pressure plate)
you could make a stop that holds the arm from retreating too far.

I can think of several explanations for the symptoms you describe but it
sounds like you've already looked at them -- 1) different "grabbiness" of the
friction material, causing some drag on the pressure plate or flywheel, 2) bad
pilot bearing dragging the gearbox input shaft,  3) air in the system, 4) a
soft hydraulic hose that balloons out, eating up some of your pedal travel, or
5) the throwout arm not properly on its pivot point.

If it persists, is there a way to alter the leverage on the clutch release
lever or the clutch pedal to cause more travel at the throwout bearing?  It's
been a long time since I looked closely at the Spit setup.

Duncan

On Jan 19, 2014, at 10:57 AM, Mike Jankowski <mikeragtopeditor at gmail.com>
wrote:

> Ok, here we go.
>
> The flywheel, etc, were all taken off the 78 engine. There is no crank float
on the replacement engine. In fact, it still had machine shop rebuild paint
and a date that was the same as the last year the car it came from ran. The
master and slave as well as line and disc were all replaced in April 2010. We
can't find any leaks.
>
> When I pump the pedal, it makes no difference. However, sometimes
downshifting is flawless, sometimes it grinds, sometimes it just is notchy. I
always double clutch downshifting anyway, so that may help. However, in
reading a few of the responses here, I think all that was on hand when the
engine was first swapped and I discovered a nearly dry master was silicone
fluid. I've flushed the system 3 times already, but am now wondering if the
combo of fluids caused this. Also, the fluid was dark and had some residue. I
blew out the line and master, but still same shifting issues.
>
> I left the transmission alone save for spinning the throwout bearing to
check it, but I'm now thinking of pulling the transmission to check the
pivots, etc.
>
> Mike
>
>
> On Sun, Jan 19, 2014 at 9:58 AM, Duncan Charlton
<duncan.charlton54 at gmail.com> wrote:
> Mike,
> No sign of leakage in the slave cylinder?  Do you have means to
reverse-bleed?
>
> I have had a slave cylinder that was very hard to bleed the air out of
completely.  You might try removing the slave from its mount, pointing the
bleeder screw upward, and using a clamp to hold the piston in the bore, and
then bleeding.  Even better, raise the slave cylinder above the master to make
sure any trapped air bubbles have chance to rise.
>
> Duncan
> (just down the road in Elgin, TX)
>
> On Jan 18, 2014, at 11:09 AM, Mike Jankowski <mikeragtopeditor at gmail.com>
wrote:
>
> > Hi Everyone,
> > I've hit the end of my rope on a problem with a Spitfire slave cylinder.
> > Here's the facts:
> >
> > Car shifted perfectly until I swapped engines.
> > Replaced 78 engine with a 76.
> > Left trans in car, never touched it.
> > Test drive after swap was good except shifting was notchy and reverse
> > ground some.
> > Opened clutch master, reservoir almost empty.
> > Topped off with fluid, shifting still bad.
> > Bled clutch, no real improvement.
> > Double checked slave cylinder to make sure it didn't get loose, made sure
> > it was all the way forward.
> > Shifting was better but progressively worsened as driven.
> > On the move shifting was ok, but hard to get into 1st, ore reverse, and
at
> > stoplight car would creep forward with clutch pedal to floor.
> > Bled 2 more times, no real change. Had to doubleclutch up and
downshifting.
> > Pulled slave cylinder, put 1964 penny as spacer.
> > Car shifted like new on test drive, and subsequent drive to grocery
store.
> > On return from store, as soon as started car could tell again not fully
> > releasing.
> > Notchiness, though not as bad, is there again.
> > Slave cylinder is 4 years and 47,000 miles old. (I drive my Spit quite a
> > bit as well as autocross it.)
> > Also, at grocery store looked at clutch master and fluid had gone past
the
> > lid, but I suspect it was slightly overfull when we left home.
> >
> > Do I just replace all the slave cylinder bits? Not really sure what to do
> > here.
> > Thanks,
> > Mike
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