If the rear on the GenIIs is anything like the GenIIIs then changing gears
has zero effect on the speedo because it will auto correct itself for the
new gears. Also, unless they bought a programmer of some sort, or had the
dealer change the pinion factor in the PCM, there would have to be a
correction box wired in to the rear speed sensor to correct the speedo for
different tire sizes.
brian cropp
-----Original Message-----
From: owner-dakota-truck@bent.twistedbits.net
[mailto:owner-dakota-truck@bent.twistedbits.net] On Behalf Of Matt Beazer
Sent: Friday, May 08, 2009 3:14 AM
To: dakota-truck@dakota-truck.net
Subject: Re: DML: Gears
I have no idea. The front airdam is missing, and one of the fenders has
been replaced and repainted with a junkyard one from a '93 Dakota (you
can see the markings from the junkyard on the top of the fender when the
hood is open) and the whole truck has been repainted at least once back
to the factory color. Wouldn't surprise me if someone had enjoyed some
off roading in it at some point, the thing is from Idaho. Not to
mention the chrome wheels are in way too good of condition, no curb
rash, rust pits or anything. Then again it doesn't have any kind of
lift I can see, so I don't know how they'd fit 33's. As you said, 31's
aren't always 31's as well. I need new tires anyway, 10.5" wide tires
wear weird on a 6" wide rim.
If they swapped the rear end they'd have to swap the front end too or it
wouldn't drive in 4wd without ripping itself to bits, and I drove it
around a parking lot at low speed before I bought it in 4wd to make sure
it was ok. 4H pops in easy, though low range is a pain to engage, but
that seems pretty typical for an unsyncro'ed low range on an automatic
tranny truck.
Let's hope the chiropractor can fix my back next Thursday so I can get
under the thing is find out what other surprises are in store for me.
Don't you just LOVE used cars? It's like buying a mystery box!
MattB
jon@dakota-truck.net wrote:
> Matt Beazer <teseract@moparhowto.com> wrote:
> [...]
>
>> Someone has dinked around with
>> this thing since if you assume a stock tire size of 235/75R15 and
>> compare it to a 31x10.5R15 tire, it SHOULD read 56mph when I'm actually
>> doing 60mph rather than what it does now, which is read 64mph when I'm
>> doing 60.
>>
>
>
> Hmmm... Any chance the truck wore 33s in a previous life? If
> someone were to install 33s and correct the speedometer to that tire,
> and then down the road the tires got swapped out to 31s without
> correcting the speedo, 64mph is exactly what your speedometer would
> indicate at 60.
>
> If my calculations are correct, the same basic result could be had
> if the speedo were calibrated correctly for the 31s and the rearend
> gears were swapped from 3.23s to 3.55s or from 3.55s to 3.91s. (64mph
> would be indicated at an actual speed of just over 58mph)
>
> Another (highly unlikely) possibility might be to have the
> speedometer left stock, switch to 31s and swap the stock 3.91 gears
> out for 3.23s. I think this would result in about 67mph indicated at
> an actual 60 though.
>
> Something to keep in mind also is that 31s aren't always 31s. There
> is a huge range of variability out there. You can't actually be sure
> the tires are 31s unless you measure them on the truck, and if you are
> calculating based on 31s when the reality is somwhat different,
> obviously that can throw things off too.
>
> Let us know if you find out what is going on there! Sure seems like
> something got changed somewhere along the line - either the speedo
> gear or the rearend gears, or maybe both. :-)
>
>
>
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