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Thank you:
I knew that there wasn't a speedo gear in my 98 but even the local
dealer says that there is.
Do you know what gear ratios we can use and still be able to get the
speedo current???
I would like to go to a 4.10 if I can.
Thanks for clearing all of this up.
Colin H.
Eric wrote:
> Hi everyone, Sense I'm working @ a Dodge dealer as a technician, I
> checked out this issue about tire sizes and speedometer readings.Here
> is what Chrysler is writing on there MDS II computer. "1997 and older
> Dakota.The instrument cluster circuitry calculates the proper gauge
> pointer position based upon a vehicle speed message received from the
> Powertrain Control Module (PCM) on the Chrysler Collision Detection
> (CCD) data bus. The PCM uses an input from the Vehicle Speed Sensor
> (VSS) and internal programming to decide what vehicle speed message is
> required. The PCM then sends the proper message to the instrument
> cluster on the CCD data bus. The VSS is a hall-effect sensor that is
> installed in the transmission (two-wheel drive) or transfer case
> (four-wheel drive), and is driven by the output shaft through a
> speedometer pinion gear. Incorrect tire size, incorrect axle ratio, a
> faulty or incorrect speedometer pinion gear, or a faulty VSS can each
> result in inaccurate speedometer readings." In other words, on -97 and
> older you can change the gear in the tranny to compensate for bigger
> or smaller tires. We can NOT calibrate speedometer with DRB III. 1998
> and newer Dakota.The instrument cluster circuitry calculates the
> proper gauge pointer position based upon a vehicle speed message
> received from the Powertrain Control Module (PCM) on the Chrysler
> Collision Detection (CCD) data bus. The PCM uses a speed pulse input
> received from the Controller Anti-lock Brake (CAB) and internal
> programming to decide what vehicle speed and distance message are
> required. The PCM then sends the proper message to the instrument
> cluster circuitry on the CCD data bus. The CAB uses an input from the
> rear wheel speed sensor and internal programming, which includes a
> programmable pinion factor to compensate for different axle gear
> ratios and tire sizes, to determine what speed pulse output is
> required. The CAB then sends the proper speed pulse to the PCM on a
> hard wired circuit. In other words, there is no tranny gear to replace
> on newer trucks. And with the DRB III you can only program the
> computer for 2 different tire sizes and I think 3 different axle
> ratio. By the way I'm new to this list. I moved to the states last
> year from Sweden, and I really like it here.I'm waiting for my new -99
> Dakota R/T 5,9 Black CC Fully loaded. Hopefully I get it before this
> week is over. The Swede/
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Thank you:
I knew that there wasn't a speedo gear in my 98 but even the local
dealer says that there is.
Do you know what gear ratios we can use and still be able to get the
speedo current???
I would like to go to a 4.10 if I can.
Thanks for clearing all of this up.
Colin H.
Eric wrote:
<BLOCKQUOTE TYPE=CITE> <FONT COLOR="#000000"><FONT SIZE=-1>Hi everyone,</FONT></FONT> <FONT SIZE=-1><FONT COLOR="#000000">Sense
</FONT>I'm working @ a Dodge dealer as a technician, I checked out this
issue about tire sizes and speedometer readings.</FONT><FONT SIZE=-1>Here
is what Chrysler is writing on there MDS II computer.</FONT> <B><I><FONT SIZE=-1>"1997
and older Dakota.</FONT></I></B><I><FONT SIZE=-1>The instrument cluster
circuitry calculates the proper gauge pointer position based upon a vehicle
speed message received from the Powertrain Control Module (PCM) on the
Chrysler Collision Detection (CCD) data bus.</FONT></I> <I><FONT SIZE=-1>The
PCM uses an input from the Vehicle Speed Sensor (VSS) and internal programming
to decide what vehicle speed message is required. The PCM then sends the
proper message to the instrument cluster on the CCD data bus.</FONT></I> <I><FONT SIZE=-1>The
VSS is a hall-effect sensor that is installed in the transmission (two-wheel
drive) or transfer case (four-wheel drive), and is driven by the output
shaft through a speedometer pinion gear. Incorrect tire size, incorrect
axle ratio, a faulty or incorrect speedometer pinion gear, or a faulty
VSS can each result in inaccurate speedometer readings."</FONT></I> <FONT SIZE=-1>In
other words, on -97 and older you can change the gear in the tranny to
compensate for bigger or smaller tires. We can NOT calibrate speedometer
with DRB III.</FONT> <B><I><FONT SIZE=-1>1998 and newer Dakota.</FONT></I></B><I><FONT SIZE=-1>The
instrument cluster circuitry calculates the proper gauge pointer position
based upon a vehicle speed message received from the Powertrain Control
Module (PCM) on the Chrysler Collision Detection (CCD) data bus.</FONT></I> <I><FONT SIZE=-1>The
PCM uses a speed pulse input received from the Controller Anti-lock Brake
(CAB) and internal programming to decide what vehicle speed and distance
message are required. The PCM then sends the proper message to the instrument
cluster circuitry on the CCD data bus. The CAB uses an input from the rear
wheel speed sensor and internal programming, which includes a programmable
pinion factor to compensate for different axle gear ratios and tire sizes,
to determine what speed pulse output is required. The CAB then sends the
proper speed pulse to the PCM on a hard wired circuit.</FONT></I> <FONT SIZE=-1>In
other words, there is no tranny gear to replace on newer trucks. And with
the DRB III you can only program the computer for 2 different tire sizes
and I think 3 different axle ratio.</FONT> <FONT SIZE=-1>By the way
I'm new to this list. I moved to the states last year from Sweden, and
I really like it here.</FONT><FONT SIZE=-1>I'm waiting for my new -99 Dakota
R/T 5,9 Black CC Fully loaded. Hopefully I get it before this week is over.</FONT> <FONT SIZE=-1>The
Swede/</FONT> </BLOCKQUOTE>
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