stainlessman

I'm looking at two different 2015 pickups...on the window sticker one says :
3.31 Electronic Lock RR Axle -$420.
The other window sticker says : 3.55 Electronic Lock RR Axle - $50.


Can someone explain the difference between the two. I tow some but not a lot. But I do plow snow. My driveway only.
Which is the better gearing? Why is one so much more cost ?
What does the electronic Lock RR Axle mean ?


Thanks for your help.

Loki 5.0

.24. and electronic locking axle locks both rear axles together . It is used in under 25mph offroad or when traction is limited like when you are stuck . You turn it on/off with a switch. About the gears, you should probably describe your driving habits and what engines and truck it is in for a better answer. The 3.55 is stock so it is probably cheaper, personally I like that gear for my application.

stainlessman

I actually went on the Ford website and had 'chat' with a Ford customer service guy. He pull up the window sticker of each truck. Even he wasn't sure why the Lock RR axle was more on one of the trucks.


Thanks for your reply. The truck would have a 5.0 and my driving style is 75% road/highway. 50-55 mph mostly. Then I tow a small enclosed trailer 5' x 8' with maybe 500 lbs in it. Or a 500 lb ramp trailer with my Polaris ranger on it at 1500 lbs. So 2000 total. I no longer have a camper to tow. I will be putting a 7 1/2' snow plow on it with Timbrens in the front. I've read a few articles on the 3.31 vs the 3.55. Sounds like the 3.55 gives you more pulling power ?

acadianbob

You are correct that 3.55's would give more pulling power. But, you are not pulling much or very often. 3.31's would work fine for you and give you better fuel mileage.

Don SC

I don't think you would see a big difference in mpg between the two diffs. I have 3.31 and would choose 3.55 just for the resale value. the next owner might have different towing needs than you do.

smokeywren

I replied right after you posted this, but somehow my Hugesnet satellite blinked and my reply doesn't show up. So here it is again.


3.31 to 3.55 is a 6.76 percent difference in engine RPM at the same speed. So if your speedo reads 2,000 RPM with a 3.31, it would read 2,135 RPM at the same speed with a 3.55. Because of the bell-shapped HP curve of your engine, you have more horses available to pull the load at 2,135 RPM than at 2,000 RPM. But HP ain't free - those extra horses require more food (fuel), so your MPG decreases slightly with the 3.55 than with the 3.32 ratio.





You want the extra horses, even if they eat more.



I suspect an error in your costs. On Ford.com F-150 build&price, the 3.31 EL lists $420 and the 3.55 EL lists for $470. One obvious reason for the $50 difference is the 3.31 ratio is standard on a 4x4, so all you're paying for is the e-locker differential. With 3.55 you have to pay for both the ratio change as well as the E-Locker.

Open axle (differential) is standard. With an open axle, one rear wheel can turn on a different radius than the other, so both rear tires can roll around a curve in the road. Also, on slippery surfaces, the rear tire with the best traction will just sit there, while the tire on the slickest surface will spin, and you're stuck. The E-locker differential is usually unlocked, so you have an open axle for drive pavement.

But the e-locker can be locked by pressing the e-locker button on the dash. With the rear diff locked, both rear wheels are forced to turn at the same speed. So both tires will turn to get you out of a spot where one rear tire is spinning while the other doesn't do anything.

Downside to a locked diff is that on a curve, with the inside tire turning on a shorter radius than the outside tire, one or both of those tires is going be drug sideways. Dragging the rear tires sideways is okay on slick surfaces such as snow, ice, mud, or even rain-slick pavement. But on dry pavement you'll quickly wear out the rear tires, and maybe damage the rear differential.

I have 55,000 miles on my F-150 that has the E-Locker diff. I live in the desert, with very little snow or muddy conditions. So I haven't needed to lock my diff very often. But when I need it, I need it bad to get me out of a mud hole or other slick spot. So I'm glad I paid extra for it.

brulaz

Also remember that a smallish increase in tire size will make a 3.55 behave like a 3.31. IOW give you the same engine rpm at a given speed.