|HOME > Surveys > Owners Results > Why Diesel|
I have the exact setup with 3.55's and hate 'em. The truck was geared too high with the stock 245/75 training wheels; with the 255/85's on it its even worse.
IMHO get the 3.92's.
I'll eventually be upgrading to 4.56's (or maybe 4.88's....).
95 1500 SLT 4X4 5.9L Auto, rear LSD
Scottsdale, AZ Rancho 9000's, 255/85B16 Thornbirds
Subject: RE: DiRT: 3.55 vs 3.92
Date: Thu, 24 Sep 1998 14:00:19 -0400
From: "Andrews, David A" <DAAndrews@IFGCompanies.com>
I've got the 4x4 1500 sport auto 360 LSD 265's with 3.55 rear. I do 80% of my driving at 65mph or up, fairly level ground. In these situations the gearing is perfect. I also drive some on the Carolina beaches, and it works fine in 4wheel low.
However, the gearing is off for slow rock/trail climbing situations.
But, I've started to use my old jeep for these situations since the going
gets tight in the woods where these trails are found (mostly mini trucks
and jeeps use them.
Subject: DiRT: 3.55 vs. 3.92's
Date: Thu, 24 Sep 1998 13:28:12 -0500
From: David Wilkinson <email@example.com>
My current setup is a QC, 5.2/5spd with 3.92's and 245/75/16 Goodyears. I have found the first gear ratio low (I'm only in first gear a few seconds before shifting) and second gear a bit high to use from a dead stop. 70mph on the freeways puts me at about 2400 rpm. I <believe> that the change to 285/75 or 255/85's will be about right as far as gearing and rpm are concerned. I should be able to have a more steetable first gear and little less rpm at the top for <hopefully> a little better mileage.
1999 QC 1500 4x4, 5.2/5spd, 3.92/LSD, HD Service/Tow Group
Subject: RE: DiRT: 3.55 vs. 3.92
Date: Thu, 24 Sep 1998 13:37:10 -0500
I have the same set-up (as Scott Nixon) and the 3.55 is a bit high.
My truck experiences a high rev downshift on hills that scares the bejeebees
out of me. 3.92's should cure this.
Steve McDaniel wrote:
When I had my 95 auto/3.54, I had thoughts of having a 3.07 or 4.10 ratio installed. The 3.07 would have allowed me to tow in direct like the 727 in your '89. A 4.10 in O/D would have been equivalent to a 2.83 ratio. Either would have been good for rpms at 65-70mph towing. The 3.54 was a little short for towing in 3rd (direct). 2500rpms at 65mph with 235/85R16s. In O/D with 3.54 ratio, it was an overall 2.44 ratio. That was way too tall for towing. At 1750rpms at 65mph, I was short on power against the wind or on hills. If my 95 auto was rated higher in the hp dept, the extra power might have added more to heat than to more power to the road. My 98 5spd/4.10 in O/D is an overall ratio of 3.03. Although I'm at 2500rpms at 70, it seems to pull with way less effort. I'm getting 1mpg better mileage with the 4.10. I thought I would lose mileage but higher rpms with less effort played in my favor. I'm getting 19.5 in town and anywhere from 10.5 to 17mpg towing. I'm starting to wonder if the 3.54 ratio is part of the problem.
I don't believe the 3.54 is the problem. My 96 4x4 has the 3.54 with 33" BFG's and is not lacking for power. It regularly pulls 10-12,000lb boats no sweat. Mileage empty city is 19.5-20. Loaded 15.5-16. I will admit that before the TST plate, the truck would need to be in 4th up any large hill. Anyhow, I would give the 4.10 some thought. If you plan to drive the truck out on the road empty as I do on long trips, the 4.10 is out of the question. Running in New Mexico when the speed limit is 75 and the trucks max speed is 78 at 2800 = no fun. I think anyone would believe that the 3.54 would deliver better mileage. 80 at 2350 is much better.
96 2500 4x4 Cummins TST, topper, 33x12.5x16.5 BFG muds.
Subject: RE: DiRT: gearing
Date: Wed, 2 Sep 1998 19:17:00 -0700
From: "Belt, Stephen D" <firstname.lastname@example.org>
> trying to understand any "con" about changing the gearing in
my truck from a
> 3.92 LSD to 4.56s. Planning for larger tires (going from 265s to 295s or
> 33x12.5s) and lift kit. I figure the mileage will drop ... and maybe I'll pick
> up some better off-the-line response?
Likely mileage will go down a bit, but not just because of the gearing change. Bigger, heavier tires are going to make your mpg go down as well.
> so other than gas mileage, what is the negative?
In your case, I wonder if you aren't going too tall on the gears. I've got 4.56 gears and 35" tires. I think this combination is at times a wee bit tall, but overall I like it. I run 70 mph at 2100-2200 rpm, with my V10 and the slushbox. If I were going at any higher rpm for that speed, I'd be unhappy.
For you, I'd expect 70 mph to be 2300-2400 rpm with 4.56 gears and 33" tires. That's a pretty high rpm for that speed, and is why I question this particular combination. If you're going to lift, and have the money in your budget for the gears, then I'd lift to clear 35" tires and run those on the 4.56 gears. I think you'll be happier all the way around. (On your tire size, I have to ask, why only 33"'s...you really don't need a lift for this tire size?)
> and do i lose the lsd or is will that remain
Quick answer, no. I changed from 3.55 gears and LSD to 4.56 gears and chose to retain my LSD. In my case, there was added cost, because the Dana 70 rearend on my 2500HD requires a new carrier for gearing above 4.10. I bought the new carrier and swapped the "guts" out from the old carrier. The added cost was ~$200.
In your case, I don't think the 9 1/4" Chrysler even requires a new carrier when jumping up to 4.56 gears, so it would be even cheaper. On the Dana 44 in the front axle, however, you'll need to check into whether there is a carrier split (tech term for do I need a new carrier?)
Lastly, a gear change is the perfect time to think about improved traction devices. By this, I mean a Detroit Locker, ARB Air Locker, or an Auburn LSD. All of these units would provide better traction control for your truck, but with each would come significantly more cost ($500-$800 per axle that you upgrade). I chose to put the ARB Air Locker in my front axle as part of my gear change, and really like the choice. In my experience its the best possible choice for front axle traction improvements, with the center disconnect axles in the Dodge Ram. In the rear I like the Auburn and Detroit units, but would probably pick a Detroit if I wanted maximum added traction. (Though I think the rear LSD has been fine for my needs, combined with the ARB up front.)
1995 2500HD V10 4x4 -- Scotts, AZ
PS - See the above URL for more details on my truck!