I'm still working the problems from my last post reguarding the cruise,
front end alignment and vibrations. I'm getting ther, but need advice on new
gear ratios. I went from stock 245/70 17s to 35x12.5 17s. This threw the
computer way off in the truck and the dealer has been trying to aviod
helping me out. The cruise issue apparantly can't be fixed with out new
gears.They set the cruise to work up to 61 MPH. Whay this number I have no
idea, I don't think the know - because no one can explain it to me.
Anyway, I was planning on installing 4.10 gears to help with big tires and
towing, but now I'm being told that shorter gears may be better? It seems my
only options are 4.10 and 4.56 - with aftermarket gears for this truck. Whic
one will help me most..I pull a 3k # trailer on ocassion and would like to
run at ~70-75 MPH with it.
Lets put it this way, a 4.56 with 35's is not much better than a 3.73
with 30's and a 4.10 would be equal to about a 3.42 to 3.55 with stock
tires. What does this mean? You want at least a 4.56 here especailly
if you want to tow anything (there is more than just effective gear
ratio here as extra lift and tire ad more drag too) A 4.88 would be
better as it would about equal 4.10's with stock tires which is not
deep at all (though some think it is) in a 4x4 truck with OD. Also,
4.88 gears are made for your axles by Yukon and you want to use Yukon
or Precision gears here.
Not when used in a Dodge. There's a listing for 4.88's in a GM 9.25", but
that's not going to help you.
4.56 is the best you're going to do, and it'll be fine. You'll have almost
the same final drive ratio as you had with your 3.92's and stock tires (just
a hair shorter, which means you'll be turning about 50 more RPMs at 65MPH
with the 4.56/35" combo compared to the 3.92/30.5" combo)
First a 1500 likely does not have a 9.25 front axle but even if it
does, "Tom" should know the a 9.25 AAM front axle made for dodge uses
the exact same ring and pinion as the GM 9.25IFS. (this was done to
limit production costs for axle) so you can use GM gears in it. There
are not two different sets or styles of 9.25 gears made as it would
not be cost productive at all. Just like Dodge started using the AAM
11.5 in rear of some trucks that uses same ring and pinion as GM app.
No different than D44's or D60's used in Fords, dodges or GM's, there
are the same unless they are reverse rotation. ALso the D50 used by
Ford in some apps uses D44 gears.
One more thing, while you comparison is close with gears, you leave
out that truck does not work in a vacum on steel wheels and it will
not give 3.92 like perfomance with 4.56's because of increased rolling
resistance and drag from big tires and lifted truck. The RPM may match
but performance will not yet so many like yourself seem stuck on the
RPM thing as being the solution. If he wants 3.92 with stock tire like
performance he needs at least a 4.88 becaice of extra drag that most
ignore. with 4.56's it will feel like maybe a 3.73 at most performance
wise and hurt towing at serious weight.
My truck uses the AAM 8" IFS and the 9.25 rear. There are NO 4.88s that will
fit in the front. Also I have 3.55 gears now, and had 245/70s from the
factory. That set up pulled my trailer just fine. I think with the added
drag of 35's the 4.56 gears should be the ticket.
Now I am scared that the dealer can't program my computer to get the cruise
and speedo correct after I change the gears. I have been there 3x since
adding the tires and the cruise only works up to 61MPH and the speedo is off
by 4 MPH once I get up to about 65. I assume this is due to the tire specs
being slightly off and stating they rotate 598 times per mile.
Guess again clueless. AAM does not make a 8.0 IFS axle. They make a
8.25 one that dodge uses too (they make a cast iron pig and alum pig
version) Again dribble from you. The blind leading the blind. Dodge
may call it a 8.0 but it is a 8.25 and uses the same gears as a GM
8.25 to keep costs down.
YG GM8.25-488R (same reverse roatation gearset as GM uses. You really
are clueless aren't you? In the link below you will see it and AAM
make a max of 4.78 themselves but Yukon makes them to 5.13. (AAM also
makes a 7.25, and a 9.25 version)
Amazing. So, the four service manuals I have, that ALL show the ring gear
to be 8.0" in diameter, are wrong? Or are you saying GMs 8.25 uses an 8.0"
ring gear? Strange that all their other differentials are named for the
exact dimension of the ring gear, isn't it?
Let's see.... here's the Dodge specs (copied straight from the 2003 FSM):
And here's the ring gear spec. for the GM 8.25 (whaddaya know - they say
Now - you tell me how 8.0" = 8.25"
I know, I know.... the Dodge manual is wrong. It's really an 8.25" gear -
they just felt like printing 8.0" for the last four years, just to confuse
people. You've actually held one of these in your hand, and personally
verified it to be 8.25", right?
Let's also remember that HomeBrewer called several different vendors and
shops, and they all told him the same story: only 4.56 available for his
axles. I guess they were all "clueless" too, huh?
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