Difference in fuel mileage in Dodge rear-end gears

I have an opportunity to buy a really clean 1999 Dodge dually with only 80K on the 5.9 Cummins motor, 336K on the body and A.T.,but with 4.10 or 4.11
rear end gears. Owner says best he gets empty is 15 mpg. I know where there is a rear end for this truck with 3.54 or 3.55 gears, like the one in my
"93 dually that gets 22 mpg, for $900. I don't do any real heavy hauling anymore. I was just wondering if any of you guys have any experience with a
"99 Dodge rear end with 3.54 gears that indicate that the one I have found would provide substantially better fuel mileage to justify the $900 price.
Also, the Dodge 2500 that the motor came out of is part of the deal. It has the 5 speed manual transmission in the bed, which I assume is an NV 4500,
plus the motor that came out of the "99. Owner says a while back when he stopped for a fill-up while driving the dually, pure water from the bottom of
the tank in the ground at the store got picked up and pumped into his fuel tank. He says he didn't realize this until later when the motor quit, had
water in it and in the injector pump. Seems to me they ought to be repairable. Any comments would be appreciated.
 
Walter, filters should have stopped the water from reaching the pump. As far as the rear ends, 3.55/3.54 will help. A 24 valve Cummins will not get near the mileage that a 12 valve will. Have both and my 12 valves will get better mileage than the 24 valves with the same rear ends and tire size. E-mail is open.
 
Some Dodge truck owners say their 24 valves get better mileage than my 12 valve does. It's confusing, but then I don't know whether they have automatics or standards, if that makes any difference. We are almost finished with the conversion we started several years ago, working as time permitted, putting a low mileage 12 valve into a "94 Chevy dually with an NV-4500 tranny. Rear end gears are 3.73. I'm thinking seriously of keeping this truck and just buying the "99 to resell it since the owner only wants $3000 for both of his trucks.
 
I have no personal experience with the 3.54 or 3.73 gears, but my '98 12v with 4.11 and auto trans (4X4) gets 15mpg loaded or empty. I don't get over 60-65mph, and if I turn the O/D off it is screaming at 55mph. Most people would hate it, but it is perfect for me and what I do with it. My friend has the same truck with 3.73's and claims 20+mpg.
 
I had a 92 regular cab 4x4 5 speed with 3.55 gears, summer time I had seen 21 mpg. Later I had a 01 reg cab 4x4 with 3.55 gears automatic which got 16-18 mpg. Then I had ext cab short bed 01 with 6 speed, I believe 3.55 gears about 18 mpg. Once I got 21 mpg on a trip which I ran 55 mph. I liked the 01 and 02 models but they say the 03 and newer common rail engines are real good on power.
 
Looks like that deal fell through. So, I'll be keeping the project truck, the "94 Chevy dually with the "93 Cummins in it and NV-4500 tranny. The rear end gears are 3.73.
 
12 valve Cummins is one of the longest life engines with the best fuel mileage and the lowest power out there.When I say this I understand I'm a big fan of the 12 valve but if you're actually going to use the flipping thing for what it's for a 24 valve is a better engine all day long. Common rail you can pretty much figure you're going to spend about $3,000 putting injectors and it at 200,000 miles and then again it 400 when you're probably overhauling the engine.Best is entirely relative to what you're going to use the thing for.
 
I've had a '99 2500 4x4 since new with 4.10 gears and a 5 speed. My truck weighs 8000. My best ever solo mileage was a trip at 55mph and I got 23.6. I can get 20 solo on most any highway trip. I get 12 to 16 towing. I love my truck and the 4.10 gears. They put me right at 2k towing on the highway which is a sweet spot for my motor. I had a '97 and I still miss the 12 valve in a lot of ways.

Dan
 

I've got 3.73's in mine and they work really well, towing a trailer on rural roads I can do 55 mph at 2200 in direct staying out of OD, on big roads stick it in OD, 1800-2000rpm and run 65-70 mph.

jr1983, several around here with 24v engines have had to replace their injection pumps at $1000.

I like my all mechanical 215 p pump 12v, changing the fuel plate and governor spring has given it the power I need, not the fastest out there but pulls plenty strong for me. It's setting in a 04 F-450 Super Duty 4x4 dually, hence my handle Destroked 450, makes a real good towing combination, fuel milage isn't the best (11-14) but it's hooked to a tandem dually trailer 90% of the time.
 
Well jr1983, I suppose this is what horse races are all about, but I look at it this way. I now have over half a million miles on my 1993 12v. Most of those miles have been pulling something, often two 5000-8000# tractors on my gooseneck trailer over hill and dale all over this country. The ONLY time I had to rebuild the inj. pump was after getting water in it. Cost me $575. I replaced all six 300 Hp injectors for $275. I roll along the interstates at the speed limit, usually 70mph. Plus, I don't have to worry about being stranded somewhere in the event of am EMP attack or a solar flare because there are no computers that would get fried. Therefore, I fail to see how the 24v engines are an improvement. True, they may be faster in a quarter-mile race, but who cares? I bought my truck to pull, not to race.
 
(quoted from post at 21:09:01 11/07/17) Well jr1983, I suppose this is what horse races are all about, but I look at it this way. I now have over half a million miles on my 1993 12v. Most of those miles have been pulling something, often two 5000-8000# tractors on my gooseneck trailer over hill and dale all over this country. The ONLY time I had to rebuild the inj. pump was after getting water in it. Cost me $575. I replaced all six 300 Hp injectors for $275. I roll along the interstates at the speed limit, usually 70mph. Plus, I don't have to worry about being stranded somewhere in the event of am EMP attack or a solar flare because there are no computers that would get fried. Therefore, I fail to see how the 24v engines are an improvement. True, they may be faster in a quarter-mile race, but who cares? I bought my truck to pull, not to race.

And there you have it. Told like it is. Electronics of any kind do not belong on trucks or tractors.
 

I still have the computer on my truck, it operates the tach and AC.
I can get by without the tach.
I refuse to buy a computer controlled tractor.

As for fuel mileage, the 1st gen Cummins engines are known to get the best overall mpg.
 
My 98 24 valve with 354 rear ends gets 16 empty it weighs just over 9000 pounds empty dually quad cab 5 speed . My 94 with the same gears and 5 speed got 17 and I use em towing they get about 12.5 to 13.5
a177596.jpg
 
IMO the only way to buy a Dodge with the Cummins in the 1990s is to get it with the manual transmission and 3.55 gears.

As for weight being hauled being too much for 3.55s, that doesnt seem to phase my buddy, he has scaled north of 40K numerous times with his. Mild fuel plate, figures 250 HP or so.

It can also get well over 20 mpg empty if kept under 2000 RPM.

Now if it had the automatic, to keep that thing alive 4.11s may not be a bad idea.

on my 90s Chevy diesels (6.5L) I run the 5 speed manual (also NV4500) and most of mine have 4.10 gears, and I hate it. too many RPMS in 4th, not enough in 5th. I am thinking of re-gearing to 3.42s and running in 4th loaded and saving 5th for running empty. I usually scale from 16-26,000 lbs combination.

I know of a guy that tows relatively heavy with his 6.5L, and he runs 3.21s, something like 1800 RPM in overdrive will do 80 or 85 mph.
 

Just curious. What makes you 3500 so heavy?
I have a F-450 with heavier frame, axles, suspension, tires and wheels equipped with a full skirted bed made from 3/16 tread plate steel that weighs 9300 lbs.
Unless your packing a aux fuel tank, welder or some other piece of equipment I'd think mine would weigh 500-700 lbs more than yours.
 
The bed is the main reason why and I?m carrying a
diesel air compressor a tool box a cab full of tools
and bed full of other tools wihen I had the bed off it
only weighed over 7000. Picture of it on the scale
a178255.jpg
 

I weighed mine right after I got it together, tool box was mounted but no tools yet, I'm using the engine mounted compressor that came with the engine (bus engine), and mounted a couple air tanks under the frame. Would like to have another air tank for more volume,thinking about mounting one in the bottom of the cross bed tool box and putting a shelf over it for tools, the box is plenty deep and most times is a cluttered mess with stuff piled on top each other.
 
My 98 24 valve long frame two wheel drive ton dually gets a constant 13-15 MPG empty. I keep an accurate mileage log so these figures aren’t estimates. I’m not sure what the Dana 80 is geared at but I’m pretty sure it’s not a 4:11. It has a five speed and at 60 MPH in fourth which I assume is direct drive the engine is revving in the 2200 RPM range. I don’t use overdrive when pulling a heavy load but if I’m pulling it hard which isn’t often the mileage drops to 7 or 8.
 
That's what I don't understand. Shouldn't the object of the Cummins people and Chrysler too be to continually improve their products? My old "93 12v
with over 500K on it still gets over 20 mpg empty, and has never gotten as little as 7 or 8 no matter how heavy the load was. So how is your "98 24V
an improvement? Plus it costs you 3 or 4 times as much as me to rebuild your pump, and over 14 times as much for a set of injectors. I just don't get
it. That's the reason I decided to put a "93 12v into a "94 Chevy dually. I'm just sick of all the new "improvements".
 
(quoted from post at 20:58:30 11/16/17) That's what I don't understand. Shouldn't the object of the Cummins people and Chrysler too be to continually improve their products? My old "93 12v
with over 500K on it still gets over 20 mpg empty, and has never gotten as little as 7 or 8 no matter how heavy the load was. So how is your "98 24V
an improvement? Plus it costs you 3 or 4 times as much as me to rebuild your pump, and over 14 times as much for a set of injectors. I just don't get
it. That's the reason I decided to put a "93 12v into a "94 Chevy dually. I'm just sick of all the new "improvements".

Walter I have asked my self that same question. Poorer mileage and a fussy sensitive and expensive injection pump. All I can think of is this was the beginning of lower emissions engineering and the early model 24 valve engines had flaws to be worked out. It’s still better than my 7.5 MPG 79 Power Wagon.
 

fixerupper: Sounds like you have 3.55 gears depending on your tire size, if they're 235x85-16's that around 31" tall.
Mine 19.5's are 32", I have 3.73 gears and mine runs 55 mph at 2200.
If your truck came with 215's the speedometer could be off just a little not showing all of the miles, but we're only talking a 2-3 miles per hundred.
Mine BIL has a 99 3500 24v auto, he claims he gets over 20 mpg, but he doesn't haul heavy, does a lot of interstate driving and drives like grandpa on a sunday afternoon cruise thru the neighborhood.
I tow heavy and often, only drove 15 miles on interstates in this truck since I got it, Mostly local roads with plenty of hills, hollows and curves here in central Ky. 13-14 mpg empty, 10-11 loaded, I think if I tune a little of the low end fuel out it may get up to 16 mpg empty and Id be good with that. It doesn't smoke bad but it is noticeable below 2200, above that it cleans up pretty good.

Walter: I have a engine mounted air compressor just like on big air brake trucks, I use the air for airing tires, running air tools and blowing off equipment out in the field. It comes in real handy but I only have two small air tanks that are only around 4.5 gallons each, this isn't a lot of volume when inflating rear tractor tires or operating a 3/4 drive air gun, another 8-10 gallon tank will double the volume and I'm thinking about mounting a automatic hose reel to get all of the loose hose out of the side box.
 

The compressor was on the engine when it was taken out of the bus so I really don't have any money invested in it, my power steering pump mounted directly to the compressor so other than redoing the oil drain to clear my left motor mount it was pretty much a bolt on deal. a few feet of air line, a couple of used semi trailer air tanks and we had onboard air.
This is a 10 cfm compressor that's bigger than any 110 volt unit, pumps nearly as much as the 60 gallon single stage 220 volt units you'll find at TSC and Lowes. Doesn't take up bed space and I don't need a inverter to run it, just start the truck up, I am looking into installing a hand throttle to bump the engine rpm's up to make it pump faster.
 
I have a 99 3/4 ton 4x4 extended cab with a 24 valve and automatic trans. I currently live in Tacoma Wa, and drive to my farm in eastern Wa generally every weekend. I fill in Tacoma and can get to the farm and back to George Wa without refilling and still have a 1/4 tank of fuel. I run on cruse control once I get on I90 @ 67mph indicated but gps says I'm at 75.

I took a trip back to Ill. a couple of years ago went east empty and bought a 14k goose neck trailer in Ill. then over to just about Indiana. Loaded a All Crop 90 on the trailer then back to the farm. I filled only once in each state I passed through both east and west, except SD since they were predicting a bad snow storm. When I got into Wa they pulled me into the scale and I was running 4600 on steers, 9600 on drives, and 7400 on trailer, all the way from Ill., over the Rockies.

This being said I thought I got fantastic mileage with the truck.

Leonard
 
Quite inventive of you. I have a similar challenge. There is no room in the usual location to mount an AC compressor under the hood of my "94 Chevy
3500 with the 12v Cummins installed, so we are considering removing the oil fill tube, replacing it with a fill point on one of the valve covers, and
then mounting a compressor just left of the inj. pump. Might be difficult to find room up front though for the condenser.
 
That sounds okay, but the only way to know exactly what your fuel mileage is is to fill er up, write down the odometer reading, drive it, fill er up again, write down your new odometer reading, then divide the number of gallons it took to re-fill it into the difference between the first odometer reading and the second one. That's your true mpg. A simple example is my Mazda Protege. It goes 340 miles on 10 gallons of gas. That's 34 mpg.
 

There's a outfit called Cummins Diesel Repowers in Mt. (Auto World) that has several different bracket options for mounting the AC compressor and alternators.
I got a set of brackets from them in order to reuse my Ford alternator rather than rig up a external regulator for a Dodge alternator.

I may have a extra oil fill valve cover, have one on my truck but they are a pain when adding oil, in goes down slow and is easy to overflow and slip oil over the engine.
In cold weather I put my oil bottles in a pan of boiling water to thin the oil so it will flow in faster.
 
my 98 24 valve long frame ton dually 2WD with 3:54 gears and 5 speed gets 16 at the very best on a long trip. Normal putz around driving is 13-15.
 
(quoted from post at 13:23:00 10/30/17) I have an opportunity to buy a really clean 1999 Dodge dually with only 80K on the 5.9 Cummins motor, 336K on the body and A.T.,but with 4.10 or 4.11
rear end gears. Owner says best he gets empty is 15 mpg. I know where there is a rear end for this truck with 3.54 or 3.55 gears, like the one in my
"93 dually that gets 22 mpg, for $900. I don't do any real heavy hauling anymore. I was just wondering if any of you guys have any experience with a
"99 Dodge rear end with 3.54 gears that indicate that the one I have found would provide substantially better fuel mileage to justify the $900 price.
Also, the Dodge 2500 that the motor came out of is part of the deal. It has the 5 speed manual transmission in the bed, which I assume is an NV 4500,
plus the motor that came out of the "99. Owner says a while back when he stopped for a fill-up while driving the dually, pure water from the bottom of
the tank in the ground at the store got picked up and pumped into his fuel tank. He says he didn't realize this until later when the motor quit, had
water in it and in the injector pump. Seems to me they ought to be repairable. Any comments would be appreciated.
y dad had a truck that was darn near the same as what you are looking at. 99 with the cummins, AT, 4x4, crew cab dually with 4.10 gears. Running around empty it would get about 18 or so. Truck was completely bone stock and stayed that way until he got rid of it.
 
Moot point now. Seller won't return my calls. Guess he changed his mind. Don't need it anyway. Finally finished the conversion project: Put a "93 12v
Cummins into a real nice Chevy Silverado dually. Runs great. Got the wiring issues worked out.
 
When either the headlights were turned on or you pressed the brake pedal, the dash gauges stopped working, the turn signals stopped working, the power door locks and power windows stopped working and the speedometer stopped working. Several people here said they were sure it was a grounding issue so we installed more grounds but the problem persisted. One person suggested it might be the turn signal switch so we put a new one in but that had no affect either. I figured we may as well change the turn signal relay and the flasher since they were the only components of the lights that we had not yet changed. That solved the problem. I suspect that the culprit was the relay because the flasher actually would work when the headlights were not on or when the brake pedal was not being depressed. But we were pulling our hair out for awhile.
 

I owned a 1980 Ford Fiesta many years ago. It developed an issue with completely discharging the battery anytime it sat for more than 2 hours. I traced the problem down to the turn signal flasher. It was some kind of an electronic device with transistors and diodes inside of a plastic box. I replaced it with a conventional flasher unit. End of problem.
 

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