Hi - Just bought a used 2006 RAM 2500 4x4. I am not sure what axle is
in the truck and was wondering if anyone out there can identify it
from the VIN (below). I know there's no LSD but I'm wondering what
LSD/locker options I have but I'm not sure which axle it is and what
ratio. This is the gas engine, not the CTD.
Many thanks in advance!
You've got the AAM 10.5" rear axle. Can't tell the ratio from the VIN - it
may be stamped on a tag on the rear differential cover.
To guestimate your axle ratio, lock out overdrive, or if it's a manual, run
it in 5th gear, at 60MPH, and note your RPMs.
Calculate the diameter of your tires as such:
If you have a 245/75R17, take the width (in this case, 245mm) and divide it
by 25.4 (converts to inches). Multiply by the aspect ratio (75 in this
case, so multiply by .75). Double the number, then add the rim diameter
(17"). So, 245/25.4*.75*2+17 is 31.46. Multiply by Pi (3.1416) to
calculate the circumference - in this case, 98.86". Divide 63360 (number of
inches in a mile) by your tire circumference - getting 640.9. That's your
axle RPM at 60MPH (1 mile per minute).
Divide your engine RPMs at 60MPH (when the transmission is in 1:1 ratio) by
your axle RPMs, and you'll have your axle gear ratio.
If you're turning 2400RPM at 60MPH, that's a 3.74 ratio. The closest gear
ratio offered is a 3.73, so that would be your gearset.
A sinpler way it to jack up one rear tire and rotate it one turn and
count drive shaft revs and multiply by two and you have axle ratio. If
it is a 4x4 you can do it with front axle because it is never
disconneted from differentail and there is no LSD up front to interfer
with this. One more thing, just for the record, the 10.5 AAM used in
that dodge is not to be confused with a 10.5 AAM that GM uses and has
for many years as none of the parts interchange (GM uses a older and
sturdier straddle mount pinion design and Dodge's AAM does not. Both
Dodge and GM do use the same 11.5 AAM axle in 8.1, Dmax and CTD
trucks. GM since 2001 and Dodge since around 2003.
An even more sinpler way might be to raise the hood and look up for a
sticker. My '99 has one there that lists all the "hardware" specifics. I
don't think they'd do away with something that convenient no matter what the
manufacturer's cost saving might be.
your way is just too easy Ken...sorry (not to mention it takes like 3
seconds and is completely accurate) *big grin*
SnoMan's way just has me getting too dirty, as i have to dig around and
get the jack out, get down on the ground and count drive shaft rotations
while i turn a wheel and you know how nasty tires get your hands. (did i
mention being on the ground? in the dirt?)
now, Tom's way...well its a lot of math, but lets face it...that's just a
cool formula, I can take my rpm number on the way to town, work, just
cruising around (who can afford that anymore?) or what ever. then next
time I'm here at the desk.....punch away on a calculator (I'd use the one
on the computer as i can never find my calculator on the desk, i have 3)
On Thu, 10 May 2007 01:50:42 -0400, Chris Thompson
Not sure where you drive but my tires are not nasty and yours are
likely not either unless you just drove through mud or oil and such.
As far as a jack, if you work on your car from time to time you should
have a extra jack or two around so not need to get yours out. You can
simply lay on a rug or such and stay clean too. It can be done start
to finish in maybe 5 minutes tops and is very accurate and in some
ways more accurate than option codes because I have seen a few that
were wrong a few times though it is rare. The speedo formula way it
prone to maybe error to because of speedo errors as I have seen them
off 10% and more which would through off axle ratio but then you could
use GPS to verify true speed and then a OBD2 scanner to varify RPM too
or just us my method if a label is lacking and be done with it while
others are still trying to do the math and check the accuracy.
Well, I just checked my '03.... nothing under the hood. However, there's
this nice little sticker on the inside of the glove compartment door, and
one of the lines reads, "Axle Ratio - 3.73".
At least you can use my method to confirm the veracity of the info. printed
on that sticker :)
(Who frequently chooses to do things the harder way)
I just bought a 2006 Dodge 2500 4x4 with the Cummins and thought the
axle ration would be in the glove box too! But not for 2006. My
salesman told me that if the window sticker doesn't show 4.10 axle
ratio, it is by default the 3.73. Just to be sure I sent an email to
Dodge with the VIN and they informed me that I had the 3.73 LSD.
I did it from home email account. I'll try to remember to check the
email address when I get home tonight. But it was through the Dodge
Website, under the "For Owners" section. Very quick and friendly
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