you are reading tiny little tires at only 17 and a half inch. Your cheapest route would be to switch to a larger tire. With the same key ring in my crew cab with 265/75/16 it runs fine at highway speeds and still does fine around town.

 

comrade you OK = a 265/75/16 tire is the same size [32.2] as a 235/85/16 but the 265 is over an INCH wider

he would hafta go to a 315/75/16 which is a 35.3 x 12.4

 

In my opinion the overdrive swap is the way to go.
A518 or NV4500 are your overdrive transmission choices, depending on wether you want to keep it an AT or convert to MT.

With both transmissions there is some fabwork involved to mate them to the NP203 transfer case.

 

285 75 16 fit on my 91 w250 , without a lift , the rims are NOT offset , nor overly wide , I do not know what diameter that equates to . It's 4.10's and 518 O.D. pulls a load O.K.

 

Honestly I wouldn't mess with it. If the truck was setup that way from the factory then turning those rpms at highway speed shouldn't  be causing any excess wear.

 

Honestly I wouldn't mess with it. If the truck was setup that way from the factory then turning those rpms at highway speed shouldn't be causing any excess wear.

I had the thought of maybe leaving the gears as well and going with a quieter exhaust running single 2.5 inch with dynomax super turbo muffler right now. Forgot to mention it has a 440 in it as well . When im at work on graveyard shift it gets slow I have way to much time I think of truck upgrades and ways to spend my paychecks lol but over drive still sounds nice.

 

Honestly I wouldn't mess with it. If the truck was setup that way from the factory then turning those rpms at highway speed shouldn't be causing any excess wear.

70's, up to late 80's trucks were made when we had the National 55MPH speed limits. That is the speed the trucks were designed to run.

 

You have the torque, so installing a taller gear or going with bigger tires will add an "overdrive" effect, giving you a higher top speed, lower highway rpms and possible increased fuel economy. The downside is first gear will also be effected, making acceleration more difficult, increased heat in the tranny when pulling, taking more power to overcome any off road obstacles, and reduced fuel economy during acceleration.

Overdrive is a more expensive option, wether it be an add on unit, like a Gear Vendors, or swapping to a transmission with OD, that will bolt to your 440. But you will retain acceleration, pulling power, and have OD for the highway.

If cost is a concern, I'd go with a taller tire and live with it.

Ed

 

is this a 2x? i'd be lookin for a 3.70 rear.

 

is this a 2x? i'd be lookin for a 3.70 rear.

you mean to say 2.70 ...

70's, up to late 80's trucks were made when we had the National 55MPH speed limits. That is the speed the trucks were designed to run.

x's 2 , it was called gearbound ( glad that stuff ended !)

 

if you change tire size or swap gears your around-town driving may be worse.  I'd either leave it as-is or add the overdrive.  Be advised tho - about 60 mph and your aerodynamics will add up real quick, killing your fuel economy, and requiring more power.  I honestly think you'll get the best performance and mpgs by not changing a thing and just let r rip.  Won't hurt the engine to spin a few more rpms, and you'll be nicely in the power curve so your mpg's may actually be the best in higher rpms  .

 

Honestly I wouldn't mess with it. If the truck was setup that way from the factory then turning those rpms at highway speed shouldn't be causing any excess wear.

Did you have in those days a 70 Mph speed limit on the Highways?

If not, I would say (if you have the means to go for it) go with a overdrive, maybe a Gear Vendors, that might be the easiest way to install? I think it would be nice to have less Rpm's.

seeing that this combo was designed for about 55Mph, and now running at 70Mph does mean that the today's Rpm's are higher then back in the days.
and, Mad Max, If I remember correctly, an engine runs most economic at it's highest torque? might I be wrong, please correct me.

 

My '76 318 liked humming along at 3000-3200rpm, which was about 60- 65mph (if you have an automatic transmission, condition of the converter is key!).
But it was not the most economic way of driving.
I got best mileage at 55-58mph (which is really slow on the german Autobahn).

Of course an overdrive increases load on the engine but it also allows running it in its sweet spot without beeing an obstacle on the highway.

 

I got best mileage at 55-58mpg

Boy, I'd kill for that kind of mileage with any of my trucks.

 

2700 at 55 is too slow for a stock empty truck I believe its the old 55 mph speed limit O.D. will be pricie for one benefit where as larger tires would give new tires and the speed difference . Use a calculator chart and see . IMO you want it at about 2k at 60-65 mph 

 

@George:


@Roy:
2k @ 60mph equates to a NV4500's 5th gear 0.73:1 overdrive with 4.10:1 axles and 235/85 R16 (or 265/75 R16 or 32") tires.
This was my target with the '76... dunno if the 318 would have enough grunt to push it down the highway loaded.
A 440 should have plenty of power to do that. And you could always out an RV draw through turbo kit on it, if it does not 

 

I run a 91 w250 318 with 285 75 16's its a 518 w/od , w 410's Its not lifted , the fenders are not trimmed , it has a front winch and a plow frame , the rims are not "deep dish" off set , the tires don't rub , not even the drag link . I'm not a flatlander , there are hills and dales here . Pulling another dodge ( truck !)on dollys it wants to stay out of O.D. Empty it is fine . I inherited the brand new tires when the girlfriend switched to a 1/2 ton 5 lug 15's , so I just tried them . they work  sadly the speedo don't  , it keeps up with traffic so..... LOL cleared up confusion

 

Did you have in those days a 70 Mph speed limit on the Highways?

If not, I would say (if you have the means to go for it) go with a overdrive, maybe a Gear Vendors, that might be the easiest way to install? I think it would be nice to have less Rpm's.

seeing that this combo was designed for about 55Mph, and now running at 70Mph does mean that the today's Rpm's are higher then back in the days.

Not only that- but remember that since the highway speed limits were 55, redline close to 70mph was acceptable.

My daily driver 78 crewcab has 727 auto and 4.10 gears and I am wanting to get my highway rpms down because I do a lot of driving on the interstate . I was wondering what everyone's thoughts would be on swapping the gears for 3.55 or some other higher ratio . Or perhaps using an adapted 518 or gear vendors unit to get overdrive . I am currently running 235/85/16 tires and running around 2700 at 55 I do no towing and only haul a heavy load a few times a year .

If you're not interested in it turning that hard on the road, that's the best reason to swap gears to taller ones. Whatever it may do to the fuel mileage, having it turn in a desirable range is a key factor- it'd likely be cheaper to regear than anything else, next the OD, then the gear vendors.

Realistically if the load's not over what the truck's rated to tow, it's not like it'd be too much for a 3.54 geared 440 truck.

 

Not having a lock up torque converter, your truck is presently turning something like 2,850 rpm @ 60 mph.  If you went to 3.55:1 axles, with the same tires you'd be turning approximately 2,460 rpm @ 60 mph.  Several people have mentioned slower accelleration, increased tranny temps and so on.  When calculating the tire size and gear ratio, my '77 D150 with a 318 and 727 turned something like 2,450 rpm @ 60 mph, almost exactly what yours would turn with 3.55:1.  No, my truck wasn't a speed demon, but I pulled plenty of 5,000-6,000 lb fertilizer carts and anhydrous nurse tanks without overheating the tranny.  As far as the accelleration goes, assuming your truck is a 3/4 ton it will weight a bit more than my truck did, but you also have a 440 under the hood and not a puny 318 like I had.  My folks had a '73 D100 with the same engine and drive train set up as my truck and that truck hauled a lot of 2,000+ lb loads of feed and trailers from Missouri to Florida and back and never had any overheating, tranny or accelleration problems.

And don't assume a lower ratio axle will hurt drivability at higher road speeds.  We used to have a '74 Newport with a 400 and 2.7 axle.  At 55 mph it was DOGGY when going up moderate hills on I-70 between Columbia and KC.  When interstate speeds went back to 70 mph, it waltzed up the same hills and the dogginess was gone.  And also consider the Newport weighed 4,500 lbs, probably no more than a couple of hundred pounds less than your truck (my D150 weighed 4,200, both weighed on MO Dept of Ag certified scales).  Your truck undoubtedly has more frontal area than the Newport, but I think everyone is over emphasizing the overheating-poor accelleration possibilities.  And were you to go to 3.55 and wanted just a bit more get up and go, switching from 235-85 to 245-75 tires would gain you back 100 of the 400 rpm you lost in the swap.  Yes, overdrive trannies are technically the best route to go, but from a labor and cost viewpoint, as long as your present transmission is functional and you can find sound axles at a reasonable cost, the axle swap is probably the simplest route.  Just my opinion. 

 

FWIW, below is a pic of a tow truck I built a long time ago. It was a 74 P-Wagon, with a fresh 413 and a 727, and 3.54 gears, and standard dually tires (235/85R16s I believe). Anyway, it got 7 mpg whether it was towing or not, and would cruise at 75 mph all day long. It had plenty of power for any speed, and would tow anything I wanted. It had dual gas tanks and I had plenty of range.

No matter what you do your fuel economy will not be awesome. I didn't care what my fuel economy was - I cared that the truck and the load would 'get there', and man it sure did. That 413 was fuuuunnnnn .

So, while I think your 440 will be just fine humming along at a few more rpms, I think if you were to re-gear the truck to 3.54s you would gain the extra top end speed you're after, and with the 440 you'll have the power you will need to push through the air. Youe fuel economy won't increase - likely it'll go down, but good fuel economy isn't the main reason you have that truck...is it

here's my old truck, "Frank" -

 

i will only put in these two more cents........i have 73 d100 2.70 rear gear 8-3/4 727, 360 with J heads and 800 T quad. it would smoke the tires with out using the brake and got about 18 mpg.
it is flat here, but i have never had any issues with any dodge trans running hot on the road if it was full of fluid.
i have never had a doggie dodge except a slant six. every one i ever had would at least bark the back tires, so i can't relate to you boys saying they are slow or doggy..........maybe its because its flat here and i'm near sea level.

 

i have messed with the numbers in the past and even re-gearing and running larger tires together would most likley cost about the same or maybe more than installing a overdrive transmission into a older truck and the overdrive transmission will most likely get you the best result since you already have 4.10 gears. i know i got 3.23 gear in my truck with 235/75r15's and i am still running about 2000rpm at 50mph which is where i most likely get the best fuel mileage. lets just say fuel mileage in it sucks. i don't know what rpm my 93 runs at at 50+mph but according to the calculater on grimmjeeper's website it should be turning at about 1425rpm at 50mph in overdrive with 3.55 gears.

 

install a constant variable transmission , some 2.70's and be done with it ? I don't speak for everyone , but I replace tires more often than I do transmissions or differential gears ....
keeping the motor at it's peak torque cannot be all that efficient or why is there 8-6-4 motors so on highway where you use the least power , it drops out cylinders ..... ( no,I don't like the older ones that do that ) ?

 

install a constant variable transmission , some 2.70's and be done with it ? I don't speak for everyone , but I replace tires more often than I do transmissions or differential gears ....
keeping the motor at it's peak torque cannot be all that efficient or why is there 8-6-4 motors so on highway where you use the least power , it drops out cylinders ..... ( no,I don't like the older ones that do that ) ?

we had an olds "short star" what a POS that was..........i took it the sale and felt bad that a friend bought it. he sold it and did ok.........maybe his conscious is better than mine.

 

yes , they did redo that thinking again , this time its better but still has to have drag from dead cylinders ,  even if they do hold valves open ... ?