[DeTomaso] Shifting

[B. Seib]

Hey Mike
What an excellent article on the issue at hand.
Please send me a copy of the picture to go with it if you don't mind. I'd
like to add it to my help files.
Thanks
Barry

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MikeLDrew at aol.com MikeLDrew at aol.com
Mon Feb 3 23:45:26 MST 2014
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In a message dated 2/3/14 11 24 22, pcajthaml at gmail.com writes:

> >It will always go into reverse when the engine is off, so turning off
> the engine, shifting into reverse is how I have been getting around the
> problem. Shifting into all other gears is smooth, whether going up or
down.
>
>>>The fact that it goes into reverse with the engine off leads me to
believe that the issue isn't a linkage problem, but rather, a problem with
insufficient clutch disengagement.   An easy way to tell, though, is to
simply
remove the shift gate, and see if that makes any difference.

Pantera vendors sell an aftermarket shift gate which has the same lateral
dimensions as the stock one, but is considerably thicker.   This illustrates
a fundamental lack of understanding of basic geometry.   The thicker
(taller) the shift gate is, the less lateral movement will be allowed before
the
shift lever hits the edge of the gate.   In order to allow equal
side-to-side
movement as a stock gate, the opening has to either be wider, or bevelled to
match the angle of the shift lever--neither of which they do.

So, if you can pull your shift gate off, then cheerfully snick into all the
gears including reverse, the problem is either your shift gate (if it's
aftermarket), or simple (but maddening) adjustment of the linkage.   If you
have a stock shift gate, it may well be that your shift lever isn't
perfectly
centered, and needs to be adjusted ever so slightly to the right.   You want
to have enough throw to the left to get it into reverse, but you don't want
it adjusted so far that 4th and 5th become problematic.

Since removing the gate is an easy test, do that first.   If that fails to
fix things, then the problem is almost assuredly insufficient clutch throw
(disengagement).   The synchros will take a bit of a beating and will allow
shifting up and down the forward gears without 100% disengagement (although
that creates wear, not a good thing) but reverse is normally recalcitrant
unless the clutch releases completely.

A PCNC member was recently struggling with this issue, and like you, he had
replaced his slave cylinder as well as his master cylinder.   In the past,
I've said that the function of the clutch is adjusted exclusively at the
slave cylinder, and the master cylinder pushrod adjustment is only used to
adjust the resting location of the pedal.

While this is true of the early cars, I failed to take into account the
monkey-motion clutch effort reduction linkage which was introduced with the
Pantera L.   While your car is early enough that it wouldn't have had it
from
the factory, mine is too, and yet mine had it, apparently retrofitted at
some
point.

There is a "T"-shaped hoozit that acts as an intermediary between the
clutch pedal shaft, and the pushrod on the master cylinder.   Once you think
about it, it's easy to see that this hoozit needs to be oriented at about a
45-degree angle (towards the rear) at rest; depressing the pedal moves it
through an arc, and it winds up at about a 45-degree angle towards the
front.
This provides maximum stroke of the piston.   (The actual value may be
something other than 45 degrees, but even if it's 30 to the rear, then 30 to
the
front, the point is simply that it needs to be more or less the same).

If the clutch master cylinder pushrod is too short, the arc then causes
movement in the wrong direction.   As the pedal shaft acts on the back of
the
piece, the front of it, rather than (mostly) going forward, instead will
(mostly) go down towards the ground, resulting in measurably less master
cylinder piston movement, with a commensurate lack of movement at the slave
cylinder.

So, first check to see if you have this piece in your system.   A photo of
the system at rest is attached, taken from the perspective of the center of
the car, looking directly outboard.

The gold-colored piece at the bottom is the support for the T-shaped piece,
whose long leg attaches to it.   The two short legs of the T-shaped piece
are attached to the clutch master pushrod, and to a pair of links which are
attached to the shaft which is rotated by movement of the clutch pedal.

(Chuck Melton has a terrific video of this beastie in action, on the
Provamo website.   Perhaps Chuck can post a link?)

The Ford TSB #10, article 89 (page 9) gives the optimum length of the
pushrod going into the master, of 2.91-2.95 inches, from the center of the
eyelet
on the pushrod clevis, to the mounting surface where the master bolts to
the aluminum pedal bracket.

(Article 88 prescribes a length for the slave pushrod of 3.07-3.09 inches,
from the center of the eyelet to the bullet nose of the pushrod, but this is
something that would be adjusted to compensate for clutch wear, different
installed finger heights for different brand clutches, etc.)

If you don't have the effort reduction kit, you can still see how proper
pushrod length is important.   You want as much of the rotational motion of
the clutch shaft as possible to be translated into horizontal motion, which
compresses the master cylinder.

Assuming there is no overt mechanical/adjustment issue, and the seals are
still holding up, then the likely culprit is air in the system.

> <I replaced a bad clutch slave cylinder about 5 years ago with the stock
> OEM unit.  I recently saw that an upgraded stainless steel slave is
> available - would that improve the situation?
>
>>>The material isn't important.   Some aftermarket slave cylinders boast
'long throw' which they achieve by using a smaller-than-stock piston.   This
results in greater extension for a given amount of master cylinder (and
clutch pedal) movement, with the tradeoff being slightly higher effort
required
due to the reduced mechanical advantage.


> > If not, how do I adjust the clutch so it disengages completely when
> hot?  I plan to change the fluid and bleed the system again, but have done
so
> many times before without an improvement.
>
> >>>An important consideration is clutch slave pushrod adjustment.   When
you depress the pedal, does it descend a notable distance with relatively
light pedal effort, before actual clutch action starts to happen?   If so,
then
a percentage of your clutch hydraulic action is being wasted, by moving the
'fingers' of the clutch fork through free space.

Have you ever had your gearbox off to see what it looks like in there?
Here is a drawing from the factory parts book, showing the lever that
attaches
to the slave cylinder, and the shaft that it is attached to; inside the
bellhousing this shaft is pinned to the clutch fork:

http://www.panterasbywilkinson.com/images/final_catalog/gif/ill13a.gif

You want the fingers of this clutch fork to be very close to, but not
touching, the throwout bearing when the clutch is engaged (foot off the
pedal).
When you step on the pedal, you want the fingers to initially pass through
free space, a very short distance (perhaps 1/8 inch or so), and then touch
the throwout bearing; further pedal movement results in the fingers
depressing the bearing which in turn releases the clutch.

If you have too much free travel here, when the clutch master bottoms out
(pedal almost against the carpet) the clutch won't be fully released.   This
can be felt easily enough from behind the wheel, if the clutch engages with
the pedal very close to the carpet.   This also can be felt at the start of
pedal movement, as very gentle initial movement with not much really
happening, followed by greater resistance.   Ideally, you want something
like 1/2
or 3/4 of an inch of clutch pedal movement before clutch things start
happening.

The aforementioned TSB has very poor guidance on establishing the amount of
free play.   It prescribes various amounts of clearance and lengths of this
and that, without really describing what you're trying to achieve, and how
to adjust things in order to get what you want.

Hopefully you can get some relief from this problem.   There is no good
reason for a car to grind going into reverse, much less be impossible to
shift.
  It's just a matter of finding the cause and eliminating it.

Good luck!

Mike