B&M 70235 TRANSPAK - Manual (Page 12)

THROTTLE VALVE MECHANISM
The purpose of the TH700-R4 Throttle
Valve (T.V.) and it’s mechanical link-
age is to control both the shift feel and
shift timing as a function of vehicle
speed and load conditions. As the
accelerator pedal is depressed and the
throttle opens, the T.V. mechanical
linkage relays the motion to the throttle
plunger in the valve body by way of the
T.V. cable. In factory installations of
the TH700-R4 the geometric relation-
ship between the T.V. cable and throttle
shaft bellcrank produces the required
T.V. cable extension (pull) to throttle
opening for the transmission to func-
tion properly. In custom installations
the correct T.V. cable mounting ge-
ometry must be accurately determined
if the transmission is to function prop-
erly. It cannot be overstated that for the
TH700-R4, proper T.V. cable installa-
tion and adjustment are paramount to
proper transmission function and life.
The following procedure will help you
design a custom T.V. Cable installa-
tion that works. The main objective is
to accurately position the T.V. cable
mounting bracket in relation to the
throttle shaft axis to obtain the proper
T.V. cable extension (PULL) to throttle
OPENING relationship.
STEP 1. Measure your T.V. cable to
establish it’s particular mounting di-
mension (there are several lengths in
use.) as follows (See Fig. 15). Retract
the slider by depressing the lock tab
then pull the cable housing until the
flats on the slider are flush with the end
of the adjuster housing then fully ex-
tend the cable by pulling the cable end
fitting out (slider must remain retracted)
until it stops. Holding the end fitting
out, measure the dimension from the
face on the adjuster housing that regis-
ters with the mounting bracket to the
center of the cable end connector.
STEP 2. Add 3/16" (0.19 in.) to the
measurement obtained in Step 1, this
is the perpendicular measurement from
the REAR FACE of the T.V. cable
mounting bracket to the WIDE OPEN
THROTTLE position of the T.V. cable
connector pin on the throttle bellcrank
(See Fig. 16).
STEP 3. The T.V. cable bellcrank must
be perpendicular (90 degrees) to the
T.V. cable when the throttle is 25
percent (1/4) open (See Fig. 16), this
geometric relationship is critical to
insure that the T.V. mechanism moves
in the correct proportion to the throttle
opening. The mounting location for the
T.V. cable connector pin will have to be
established on the throttle bellcrank at
a radius of 1.094 / 1.125 in. There may
a suitable existing hole at the correct
radius on the throttle bellcrank,
otherwise you will have to fabricate an
attachment to the bellcrank that will
properly locate the connector pin. Diagrams of several typical factory in-
stallations are shown for reference (See
Fig. 17), notice the geometric relation-
ship between the T.V. cable bellcrank
and mounting bracket.
Several things should be kept in
mind during this stage of the design:
1. The proper location of the T.V. cable
mounting bracket is determined by
the angular and radial position of
the T. V. cable connector pin on the
throttle bellcrank.
2. Make sure that all of the cables or
rods that will be attached to the
throttle bellcrank do not interfere
with each other when the throttle is
advanced from idle to wide open.
3. Mount the T.V. cable adjuster
housing so that the locktab is readily
accessible and not blocked by other
cables, rods, brackets or
accessories.
STEP 4. Fabricate T.V. cable bracket
using 0.090 - 0.125 in. sheet metal
(See Figure 18) for the adjuster hous-
ing cutout dimensions. If you use the
thicker stock a chamfer will be required
on two sides of the cable mounting
cutout to allow the lock tabs to expand
properly. The T.V. cable adjuster re-
quires a pull of about 18 lbs. to ratchet
out, so try to make the mounting bracket
as rigid as possible. If the mounting
bracket flexes the T.V. pressure will
not be consistent.
Figure 15
12
Measure this dimension
(with other end attached
to linkage)