From: John De Armond
Subject: cruise control product review
Date: Tue, 14 Mar 2000 05:59:14 EST
I recently installed a new cruise control on my motorhome. This is
a mini-review of the installation and the product.
My MH, a 1982 Itasca 22 ft Class C, came with a factory-installed
Dana cruise control. It did not work well because the relatively
small engine does not produce enough vacuum to operate the cruise
control's vacuum servo, even with a vacuum reservoir.
A few years ago, Dana spun off their cruise control business to a
new company called Rostra. Rostra makes a wide variety of cruise
controls that are OEMed to other vendors, ranging from many motor
home manufacturers to J.C. Whitney and Penney's. They make both
vacuum-operated units for gas engines and electrically operated
units for diesels and applications where there is insufficient
engine vacuum. I chose the UltraCruise II which is an electrically
operated unit. I bought it from a hotrod supply store. Cost was
The unit consists of a servo box containing an electric
motor-operated throttle actuator and a microprocessor board, a
vehicle speed sensor for the brand of vehicle you specify at the
time of order, a turn signal or dash panel mounted control head and
a bag full of misc hardware. Installation consists of attaching the
actuating cable to the throttle linkage, mounting the servo box
somewhere convenient, setting some switches in the servo for the
application at hand, installing the speed sensor on the speedometer
drive (if needed) mounting the control head and providing power to
The cruise has several inputs. For a gas engine, the inputs are
vehicle speed, tachometer, brake actuation and ignition switch
power. For diesel applications, the inputs are vehicle speed, brake
actuation and if there is a manual transmission, clutch petal
actuation. The latter is necessary to kick the cruise off if you
press the clutch. Otherwise the engine might be over-revved as the
cruise tries to maintain speed.
There are 3 major options for vehicle speed:
* The Vehicle Speed Sensor (VSS) that attaches to the speedometer
cable on vehicles with mechanical speedometers.
* The VSS signal from the chassis control module for vehicles with
electronic speedometers and/or electronic transmissions.
* Magnets attached to the drive shaft. This is for vehicles for
which there is no VSS. This is the older, more traditional method
used for aftermarket cruise control systems. It is reliable if the
magnets are properly attached to the drive shaft.
The UltraCruise II can use any of the above three methods and is
selected via a configuration switch. A "Technical data" booklet
comes with the system that lists where on each late model vehicle
the VSS signal may be tapped. My motorhome uses a mechanical
speedometer so I ordered a VSS for a chevy automatic transmission.
Installation involved nothing more than unscrewing the speedo cable
from the transmission, screwing the VSS sensor to the transmission
and attaching the speedo cable to the VSS sensor. The wire from the
VSS sensor is routed up the fire wall to the servo module.
The tachometer signal is taken either a) from an HEI ignition TACH
terminal, b) a specified lead on the Ford electronic ignition, c)
specified pins on the chassis control module for late model vehicles
or d) a coil terminal for all other types of vehicles. On my
vehicle, I had only to slip a connector onto the HEI's "TACH"
terminal. A tach signal isn't strictly necessary but one loses some
engine protection without it.
Diesels obviously don't have an electronic ignition signal to grab a
tach signal from. Even the electronic diesel engines may not have a
convenient tach signal. This unit is designed to work without a
tach signal. If a tach signal is present, the microprocessor
compares the tach and vehicle speed signal and trips the cruise if
there is too much deviation. With an automatic, such deviation
would mean that the transmission had been put in neutral or the gear
has been changed. For a manual transmission, that would mean the
transmission had been put in neutral or the clutch is slipping. A
"manual/auto" configuration switch sets up how much differential is
tolerated. Almost none for "manual", enough to allow for torque
converter slippage in "auto". If this function isn't present, one
could put the transmission in neutral without the cruise control
knowing it. Seeing the vehicle slowing, it would yank the throttle
open, trying to regain speed. The engine, of course, would be quite
unhappy with this. With this feature, it sees the vehicle slowing
while the engine speed is increasing and so trips the cruise.
A "diesel/gas" configuration switch defeats this function for
diesels and other engines that might not have a convenient tach
signal. It takes some care to protect the engine under these
conditions. Rostra recommends putting a switch on the clutch
pedal. It also suggests hooking to the neutral switch on auto
transmissions. Protection of a manual transmission isn't
conveniently possible unless the transmission has a neutral switch.
Other configuration switches include "gain" to control how tightly
the speed is controlled, "centering" which controls how much initial
throttle is introduced when the unit is actuated, and how fast, and
a diagnostic mode which will allow one to check all sensors without
test equipment. For my rig, I set the gain to "high" and the
centering to "fast". More on that later.
The unit requires two sources of power, battery and switched 12
volts. The battery voltage holds up the CPU's memory - the unit
appears to learn the vehicle's dynamics. The switched 12 volts
turns the unit "on". I grabbed both signals from my MH's chassis
Installing the throttle cable was trivial since my MH already had a
cruise control. Installation involved little more than removing the
old throttle cable and hooking up the new one. The kit comes with a
large selection of brackets and do-whitchets necessary to hook up to
various types of throttles. My experience in installing the Rostra
on other vehicles is that the kit is complete.
Installation of the control head was simple since the previous
installation used the same head. I simply used the old one. It
mounted on a shortened Chevy turn signal. a wide variety of
OEM-type stalks are available. If all else fails, a universal dash
mounted module is available.
After I got all the wires hooked up, the throttle connected and the
servo mounted, there was little else to do other than to check the
configuration switches. The book has a nice worksheet for figuring
out the switch positions but I didn't really need it. I static
tested the unit by hooking a pulse generator up to the VSS input to
simulate a moving vehicle and then activated the system. The servo
yanked the throttle open and then tracked my changes in the pulse
generator frequency. I verified that the various inputs worked.
lacking test equipment, the servo may be put in test mode. An LED
will flash when a VSS pulse is received and when the various inputs
are actuated. In reality, I could have just done a drive test, the
installation was so simple.
Operation involves simply bringing the vehicle to the desired speed
and pushing the "set" button. It grabs the throttle immediately,
though not as fast as the vacuum version. Speed control is
excellent. They appear to have implemented a full PID controller.
With such control, it not only does whatever is possible to maintain
the set speed, it anticipates load changes through derivative
action. When the base of a hill is reached and the very first bit
of incline is encountered, one can feel the throttle yanked very
early and more than one would anticipate. Similarly, when cresting a
hill, the throttle is closed before the peak is reached. Very nice.
The brake signal is taken from the brake light switch on the brake
pedal. This signal trips the cruise control off when the brake
pedal is pressed. A configuration switch on the servo head controls
whether this lead causes a trip on the presence or absence of
voltage. My brake system switches 12 volts to the brake lights so I
selected trip on the presence of voltage.
With the gain set to "high", the control was a bit abrupt. The
throttle would slam shut at the top of a hill. The speed wouldn't
over or undershoot by any significant amount but the sudden change
in acceleration was uncomfortable. I set the gain to "medium" and
all was swell. Speed control is still within a MPH until the
throttle is yanked wide open but the harshness is gone.
I noticed that the control improved after the cruse had been
operated for awhile. That indicated that the CPU was self-tuning
itself to my vehicle's dynamics. I tested this by pulling the
"battery" fuse, clearing its memory. Sure enough, the control
degraded to the as-installed state but quickly improved again.
All in all, this is an impressive package. It controls better than
any OEM cruise I've ever used. The servo stroke and strength is
enough to operate almost any sort of throttle. The installation is
easy - took me about an hour, most of which involved dismantling the
engine cover and removing the old system. System has a 3 year/36000
mile warranty. I've had it for about 6 weeks now and have been on 6
trips. Very pleased with the performance. Highly recommended.
PS: I originally ordered this unit from JC whitney - back in
November. They backordered this "custom" system. They dutifully
sent me postcards telling me the system wasn't ready. Until I
canceled in Feb and ordered elsewhere from a vendor who had it on
the shelf. Autozone sometimes has this system, though they don't
carry the myriad of turn signal stalks. This is a special order
item for them.