Re: 3.91 gears ???

From: Andy Levy (andylevy@yahoo.com)
Date: Wed Jun 12 2002 - 22:36:16 EDT


Neither, Tim.

On '98s and newer, the speed sensor is located "after" the rear-end
gears. At that point, the only thing between the sensor and the road is
the wheels.

Think of the speed sensor as being on the rear axle (it's physically
clsoe enough for us to make this assumption). At 70 MPH, the axle is
always turning the same speed, regardless of the axle ratio, given the
same tire size.

On '97s and older, the speed pickup is on the transmission output shaft,
so changing the gear ratio will change the speed sent to the computer.

Tim Althoff wrote:
> ok so all this talk has me all messed up! does it make your Speedo fast or
> slower? simple answers...
>
> Tim Althoff
> 99 V6 RC 5-speed SY
> http://www.yllwdkta.com
> http://go.to/ohiomeet
>
>
> -----Original Message-----
> From: owner-dakota-truck@dakota-truck.net
> [mailto:owner-dakota-truck@dakota-truck.net]On Behalf Of Ronald Wong
> Sent: Wednesday, June 12, 2002 10:09 PM
> To: dakota-truck@dakota-truck.net
> Subject: RE: DML: 3.91 gears ???
>
>
>
> You're mistaken. The RWSS (rear wheel speed sensor) sends the signal to the
> CABS (computer anti-lock brake system) which gets the tire size entry from
> the PCM for the speedo calculation. If everything you said was true, then
> you would be right, however, the rwss sits between the differential and the
> rear wheels. That means the rwss picks up the rotation of the wheels but
> has no idea of the difference between the ring and pinion gear. You're also
> limited in the size of wheel you choose for your Dak. The table in the PCM
> contains approx. five entries. Those are the wheel size it came with plus
> four other pretty much standard size wheels (tires and rims combined). If
> you get a size that is out of the ordinary your speedo will be off if you
> get to the nearest setting to the correct one. Before anyone asks, the
> changing of the entry that your PCM will pick requires a flash to the PCM
> from the dealer. Depending on how well you know your dealer, or vice versa,
> that flash can cost up to $75 USD.
>
> Ron
> 00 PB SLT QC 4X2 5.9 46RE 3.92 LSD
> For modifications see my DML Profile (URL follows)
> http://www.twistedbits.net/WWWProfile/dakota/Kw9pV1EkFeOYY
>
>
> -----Original Message-----
> From: owner-dakota-truck@dakota-truck.net
> [mailto:owner-dakota-truck@dakota-truck.net]On Behalf Of Jon N. Benignus
> Sent: Wednesday, June 12, 2002 6:49 PM
> To: dakota-truck@dakota-truck.net;
> dakota-truck-moderator@bent.twistedbits.net
> Subject: Re: DML: 3.91 gears ???
>
>
>
>
>>Only a tire
>>size change will affect your speedometer.
>
> I don't think so.
> A taller tire is in effect raising the gear ratio, therefore the axles and
> driveshaft turn slower. Going to a taller gear does the same thing.
> The sensor measures pulses on the axle or driveshaft depending on the speed
> they turn, right? Lower gear, axles, driveshaft and engine spin faster gor a
> given speed, therefore more pulses, higher speedo reading.
> Correct me if I'm mistaken.
>
> Jon
> STL MO

-- 
-andy
andylevy@yahoo.com
Maintainer, DML FAQ - http://www.dakota-truck.net/faq/
http://home.twcny.rr.com/andylevy/dakota/
'99 CC 4x4 318 auto



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