Miles per gallon T-case or transmission

[army70deuce]

About to take ownership of first M35A2, assuming GovLiquidation doesn't screw up my paperwork again, but anyway here is my question. When I get back from Iraq deployment number 2 with some cash in hand I was hoping to increase my MPG. My understanding is that MPG is due to wind resistance and RPM and since the Deuce is a moving brick to increase MPG I need to decrease RPM. Which would cause less problems/hassels, changing the gear ratios in the Transfer case to say .75 to 1 instead of 1 to 1 (.75 is just a random number I chose) or changing the transmission to one with more gears? After reading other threats it seems that the transmission would be more difficult with having to get adapters and with the PTO winch etc. While the T-case would be easier and I could beef up the gears in there at the same time.

Any thoughts, opinions are welcome, Thanks for the help.

EOD....Yes we really are crazy

 

[Chinookpilot77]

Well first, the deuce is geared so low for a couple of reasons. One is due to the engines relatively low power to weight ratio when compared to the weight of the truck. That is why you have that 1:1 and axle ratios of 6.72:1 (most civilian truck applications are 4.11:1 or 3.73:1) Another reason the deuce is geared so low was that its primary goal was to be an effective offroad transporter, yet still be an effective ON road transporter...so once you start messing with those ratios, you are going to start skewing those balances in the favor of one direction or the other.

When thinking about extra gears, I usually have to downshift on long grades to get up these Alabama hills. the deuce's engine just doesn't have the power. I dont see how more gears would help all that much. MAYBE on the straightaways?

All that being said, the engine is great at what it was designed to do, and I wouldn't change a thing about it, or the transmission.

Just my .02 bud. Do whatever you'd like with your truck, just pointing a couple things out.

 

[Chief_919]

Just my .02 as somebody who has worked on these things for 17+ years- anything you change to increase fuel mileage is going to decrease performance and "felt" power.

Instead, if it is range you are concerend about, I would look at adding more fuel capacity. If it is fuel cost, I would look at running alternative fuels..

 

[GoHot229]

mabe a better route would be 11.00's and lockouts for MPH & MPG respectivly

 

[72cj5]

Like he said the motor is too weak......If you wasted all your time and money to change gears and it might only give you 2 mpg.......I would single it out on some 395's and you will have changed the gear ratio and made the truck look like a beast all in one lick.

This is my two cents.

 

[dittle]

Take the tarp/bows off, that will help your MPG as you're not pushing such a big brick through the air.

 

[Recovry4x4]

If after all this you still want to regear, M35-tom is making a deeper OD gear for the deuce tranny. Paying for R&D and mfg of different transfer case gears will easily outcost your truck 4 fold. The bigger tires is the most sensible option.

 

[ken]

Lock out hubs gave me 1 1/2 MPG. I run all ten tires at 65PSI when on road. And try keeping the the truck at 45MPH. Slowing down makes a big difference in milage. And it keeps the engine at it's peak tourque. Where it is at it's most efficent. If you run a civi vehicle at its max speed it won't get good milage eather. You should be able to get 10MPG easily unloaded. Even My M52A2 got 9MPG bobtailing home from San Antiono. For what it is, It gets pretty good milage.

 

[Ferroequinologist]

I get 8-10mpg in my stock 109 if I don't constantly drive it 'balls to the walls'

 

[army70deuce]

Thanks for the imput, I was mainly trying to increase the range, and after consideration agree that additional fuel storage will be easier to set up and cheaper than messing with the gears.

 

[Capt.Marion]

The truck was designed for a particular purpose, and did a damn fine job. Changing the truck to try to suit it to a different purpose won't do any good.

My suggestions: lockout hubs on the fronts, taller tires, and running singles in the rear. That's about the most of what you'd want to do.

 

[Driver523]

Here's is the results of adding a Aux. gear box, alot cheaper then some other deals, and, with a three speed box ( low--direct--overdrive ) you can use the overdrive for rear wheels ( Hiway ) and then go to direct for the use of the front end if you want---not sure about the milage thing but I think its the best way to get gearing--%s can be 17% and 26% that I know of----Here is the thread----Driver
http://www.steelsoldiers.com/deuce-modification-hot-rodding/26335-1970-duce-restored-7041-spicer-aux-gear-box.html

 

[SasquatchSanta]

From strickly a mileage standpoint I'm not sure how much going to 395 tires will help on a tendem (6X6) truck. I say this because of the unsprung weight factor. Yes the larger tires lower RPMs but they are also heavier and heavier tires are horsepower (fuel) thirsty.

Since I've only had experience with 395s on a bobbed deuce I don't know what RPM is required to run 55 or 60 MPH with 1100 tires. I would think running single 1100s with spin out front hubs would be best "IF" they will allow you to cruise without going over 2,400 RPM.

An LDT engine gets it's max economy and torque @ 2,000 PRM. At 2,200 and 2,400 RPM efficiencies drop a little BUT over 2,400 and fuel economy quickly heads south. At 2,600 it's time to start looking for an Arab with his own oil well to co-sign a note when you buy fuel.

I personally feel, and I "think" others will agree that if you can keep the multi engine (never) under 1,600 and (never) over 2,400 they will last a LOT longer. Fortunately, this RPM rangeis also in the best economy envelope.

If you're not going to use your deuce to haul heavy loads which you probably won't be after talking to your insurance agent, you might want to experiment with not only the main fuel setting on the injection pump but also (and especially) with the droop screw setting. The droop screw controls fuel delivery from idle to 1,600 RPM and I personally think they are set too rich on a lot of pumps. If you turn it down and don't like the way it runs you can always turn it back up. I've turned the main fuel and droop settings down on my LDS engine and it still runs like a scalded dog. IP pump setting have been covered extensively --- go to search.

Good luck.