At 01:36 PM 3/5/99 -0500, Paul Tegler wrote:
>I agree with Barney's statements concerning cruise controls with 4 bangers
(vacuum limitatons) except for the statement concerning not using the
magnets. According to most instruction sheets, yes this is possible, but
not advisable with a clutch. Any slippage would result in the cruise
control erraticly trying to control speed, possibly surging or completely
dropping out. Using the magnets on the driveshaft, picks up a much more
consistant speed sense, and eliminates the extra wiring and circuits
(inside the cruise control) that would add an electrical load to the to the
coil circuit. In some cases it's also been known to interfer with proper
tachometer operation.
I think Paul may have some of this a little backwards. I believe the
instructions normally recommend using the magnets if you have an automatic
transmission, because the slippage in the torque converter allows a
variation between engine speed and prop shaft speed, so the tach wire on
the coil might not give you a steady speed.
The circuits for both the magnet hookup and the tach wire circuit are
included in the harness and the controls. Using the magnets requires that
you also install the small wire harness from the control unit to the
magnetic pickup (as well as the magnets and a bracket to hold the sensor),
which would be extra complexity and extra work to install. I have
installed several aftermarket cruise controls, and I have never used the
magnet setup with a stick shift car. It works fine without the magnets.
The one tach wire that hooks to the coil is only a sensor wire, draws no
measurable current, has a diode in the circuit, and will not interfere with
anything else in the car. However, there is an admonition not to route the
tach wire too close to high tension spark wires, because the HT surge could
cause an induction error reading on the tach wire. Just don't tie-wrap the
tach wire to the coil HT wire and you'll be fine.
Most (if not all) of the new electronic controlled cruise controls have
over-rev control logic, such that if you depress the clutch and the engine
speeds up, a change of about 15% in engine speed cuts off the cruise
control and releases the throttle immediately. These units do not require
a clutch switch (in direct opposition to what it says in the J.C.Whitney
catalog), and in fact do not even have a circuit to connect a clutch
switch. If anyone wants the clutch switch that I bought (per JCW catalog
instructions) and cannot hook up to my cruise control, they can have it for
$1, which should cover the postage.
The last time I installed a cruise control in my MGA, I mounted it inside
the passenger compartment, just above the driver's shins, attached to a
couple of the master cylinder bracket bolts on the rear side of the
bulkhead. The working end of the pull cable was attached under the heater
shelf and pulling on the throttle pedal arm right where the stock throttle
cable attaches, also inside the passenger compartment. Electrical power
(with included in-line fuse) was picked off the ignition switch, ground was
attached to the body under the dash, and the control panel (operator's
switch panel) was attached to the bottom edge of the dash as the only
visible part inside the car.
Under the bonnet, the only visible clues to the cruise control were a small
vacuum hose from the intake manifold running through the firewall, one wire
to the ignition coil, and two wires to the hydraulic brake light switch.
If you have (or install) a switch on the brake pedal near the driver's
toes, you can keep those two wires inside the passenger compartment as
well. As often as I'm servicing things under the bonnet, it's nice not to
have the added gadgets in the way. The engine bay is less cluttered and
looks more stock without the extra parts in there. And if you really don't
mind the bother, you can hook up the magnetic pickup on the driveshaft and
eliminate the wire in the engine bay going to the coil. Sorry, but I don't
know how to eliminate the vacuum hose with this type of control unit.
If you use a vacuum canister to stabilize the cruise control during heavy
throttle operation, just put the canister anywhere in line between the
intake manifold tap and the cruise control actuator. The canister should
have one check valve in the line between the canister and the intake
manifold to prevent air from flowing from the manifold back into the canister.
Been there, done that, usually a two hour installation, always works great.
Barney Gaylord
1958 MGA with an attitude
http://www.ntsource.com/~barneymg
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