I have been away for a while, because work has been grueling. However, I have had time to perform an upgrade to my truck to significantly improve the fuel economy and overall drivability of my truck without diminishing it's hauling capacity. I have a 1996 2wd F-150 with an NP-435 and an EFI 300. At one time I had a 3.08:1 axle ratio in my truck. These gears worked well, and my truck got about 16 MPG average, and on the highway it would get 20 MPG at 55 MPH. Also, when towing, I could easily pull 8,000 lbs and I only needed to use 1st gear when starting a big trailer from a dead stop on a steep hill. At 260,000 miles or so, my original axle went bad. I didn't have time to lay the truck up while I fiddled with it, so I called the local wrecking yard for an axle, and they had one pulled and ready to go. It was a 3.73:1 axle. I wasn't thrilled but I needed to get to work, so I bought it and installed it. My mileage dropped severely; at 55 MPH I was only getting 12.9 MPG average. It actually hurt my pulling power, because at highway speeds I was so far above the engine's sweet spot, I would loose speed on hills, and the truck worked hard to pull the same trailer it had pulled so easily before. But then I had a stroke of good fortune. I found a really nice 1989 F-150 4x4 with a bad engine that I bought for $500 to fix up and sell. I also found a T-boned 1994 F-150 for parts, that cost me $300. So while swapping the engine from the 1994 into the 1989, I realized that the '94 had the 2.73:1 axle ratio, and I decided to swap it. I installed the 2.73 axle into my truck 2 months ago, and began keeping records. My fuel economy jumped dramatically and is even better than with the 3.08:1 gears. My average for the last 2 months has been 18.1 MPG, and at 55 MPH with no load I am now getting 22.4 MPG. I towed the 8,000 lb trailer with the truck in Pennsylvania on some steep hills in the Poconos, and she did it with no trouble. In fact, on a few steep hills I did have to gear down to 3rd (which acts like 4th would if I had 4.90 gears) and maintained 55 MPH no sweat. I do need to use first gear to move off from a dead stop with a heavy load on uphill grades, but 1st gear is actually usable now, and I still only need it with a heavy trailer. I am extremely pleased with this swap and have to say that my truck is much more pleasant to drive. This might not be the ideal gear ratio with an overdrive transmission, and definitely would not pull anything with an M5OD, but it might be something for some of us to consider if we are running HD 4 speeds. The nice thing is that someday, when I install a 4BT Cummins (the only engine I'd replace my 300 for), I'll already have the right gearing in place.

 

good read. i have the m50d with a 2.73 rear. the truck has ***** to pull stuff, but my clutch is terrible. it will burn up too easily. with a tougher clutch, i think the m50d would be a much better tranny. i also get really good mpgs like you. your truck came from the factory with a 4 speed?

 

I have the 300/5speed/3.08 combo....hate the gears....Going to 3.55's...

 

my bronco has an np235 and 3:55's I originally bought my 88 for the m5od to go into the bronco, then made a deal with my dad to get the dual range. and while according to its tag it isn't the overdrive, i figure thats ok, and maybe even better. it will turn my 3.55's into 4:10's while in the low side, and with 33's it should knock my cruising rpm down. plus having an option of 8 gears should allow me to keep the engine in the sweet spot way more than 4.

with a wide band controlled megasquirt-injected 300 I am hoping for mid 20's

but first i got to get home and finish putting it all together.

 

stupid double post...

 

Octaneforce: No, this truck came with an M5OD. The NP-435 was swapped in.

 

does it still have the puny 10 inch flywheel? i dont understand why ford did that with the 300.

 

You mean 10" clutch? No it has the larger one (I forget the size... it was a long time ago). I ordered a clutch for an 86 F-350 with the 4.9L (that's what my transmission came out of). I think it's either an 11" or 12". The flywheel is also from the 1986, because I had it machined before doing the swap. I thought the flywheels were the same size though, but like I said, it was a long time ago (1999 I think).

 

my 89 4.9 has an 11", the same as the 302.

 

oh maybe your right. the flywheels might be the same but the clutches might be different sizes on the different trucks. whatever lol. you have a truck that can pull like a tractor and still get 20 mpgs. sounds good to me.

 

That was the point. It only took me 300,000 miles to figure out the formula!

 

Oddly enough, Ford had it figured out more than 30 years ago. It was common to find 2.47, 2.75 or 3.00 gears behind a 300 in the late 70's and early 80's, when OD transmission's were not common.
Another oddity, those 2.73 gears were only used behind a 300 and 5 speed. Not great for pulling a load, but they could pull some MPG's........

 

I had a 83 Ford Chateau with a 300 4 speed with 2.73's. She was a lazy pig, but it got great gas mileage for its size.

 

I have the same combo, going to a ZF for the creeper first when loaded

 

I have the 2.73:1 and it gives me great fuel economy. I hated the M50D so I had a ZF-S542 installed, and have fantastic pulling power 1st-3rd, with the bonus of .76 OD vs .80 for the M50D.

I rarely use 1st -- it's so steep.

If I put 32.5" on the rear axle I can get down to around 2.51 final drive. That might be awesome for fuel economy!