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Need some advice concerning the difference between a 315 and a 355 in the F150 EcoBoost...we are pulling a trailer 8000 empty....which is the better rear end to get...want to order it new....will be traveling out west 2 or 3 months of the year but a majority of the time we will use the truck around the city or countryside---315 will pull 8600 the 355 will pull 9800 lbs...any suggestions..this is my first time on this site
 

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I would go with at least the 3.55, but a 3.73 would pull more weight, if you ever need to pull anything heavier. I would also pick the limited slip diff over the locker.
 

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Go with the 3.73 IMO. It will run just under 2k RPM at 70 MPH. I have the FX4 18" tires and trailer tow pkg. I decided against the Max Trailer tow because my trailers are not wide campers or 8' wide box trailers.

But if your trailer is extra wide around 8' then go with the Max Trailer Tow and get the extendable mirrors.

I had the exact same set up in my 07 with the 5.4. and was pleased. But now with the Ecoboost power is great! And mpg should be the same if not better.

I special ordered my 13 and only took about 4 weeks to get it in.
 

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Mt toy hauler weighs right at 8000 punds loaded with a week's worth of junk and the RR. I have 3:55s on it and have pulled it up Raton Pass at 65 going both ways twice. Its been over three 12,000 ft mountain passes (several times) and didn't even hiccup. Up Monarch pass as fast as you can go with any vehicle. It'll downshift when it does but it pulls great. My 1200 mile average for both trips to Taylor Park was 9.2 mpg. I have about 5000 miles dragging this trailer to the dunes, river runs, and the mountains and love the way it will pull. 3:73s will pull better and I would have loved to have them but the truck I found that fit all my needs came with the 3:55s. Two days ago, I got rid of the red one you see in the picture for a 4X4 but the gears are still 3:55s. You won't be disappointed with the 3:55s but if you can find one and it fits your bill, the lower gears will definitely help in the pulling department.
 

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Need to not only consider weight but wind resistance as well. I used to pull a 24' Haulmark that was virtually empty normally. Had a special circumstance where I had to load a 3600 lb. car and tow over the WV Turnpike. Extra weight made virtually no difference in fuel mileage with the Dodge Cummins I was using at the time. Pulling into a hard headwind, however, was another story. Factoring the package puts you in at least 3.55 territory but the max package would be a consideration for sure!
 

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Need to not only consider weight but wind resistance as well. I used to pull a 24' Haulmark that was virtually empty normally. Had a special circumstance where I had to load a 3600 lb. car and tow over the WV Turnpike. Extra weight made virtually no difference in fuel mileage with the Dodge Cummins I was using at the time. Pulling into a hard headwind, however, was another story. Factoring the package puts you in at least 3.55 territory but the max package would be a consideration for sure!
Amen. This trailer I have is a brick as far as wind resistance. My towing mileage varies greatly with the degree of headwind. My worst ever was going from Clayton, nm to Raton into what I figured was a 30 mph headwind for 80 miles. 6.2 mpg.
 

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Jam, there are a lot of factors to consider. You mentioned the 3.15 and 3.55 ratios, but there is also a 3.31 to consider. Right now you have an 8,000 lb. trailer empty. I would think the 3.15s would be a bit small after you get some supplies/gear/clothes in there for a trip. Plus, what does the future hold? Will you be getting a bigger trailer in the years to come, even if it's not in your plans right now?

You should be able to order the trailer towing mirrors without the Max. Trailer Tow package. For the rest of you...did you know the 2013's with the bigger mirrors are now electric folding?

If I understand correctly, you're looking to get the best mileage while in town but still have enough ratio for towing when needed. When I traded my previous vehicle in for the F-150, both my transmission and transfer case were leaking, I assume mostly because our camper max'ed out the tow rating. This is why I would be leery of the 3.15s in your case.

Let us know what you get.
 

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What is the disadvantage of the locker in regards to towing?

I would go with at least the 3.55, but a 3.73 would pull more weight, if you ever need to pull anything heavier. I would also pick the limited slip diff over the locker.
 

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The locker is selectable, and should remain "unlocked" until you need it. There is no disadvantage. The advantage is that you can engage it when needed such as pulling up a boat ramp, or up a steep dirt road incline.
 

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The difference between limited slip and an electronic locking differential is substantial. Limited Slip only works if both tires have some kind of traction and doesn't stop your tires from slipping, but rather limits the slip (hence the name). An electronic locking differential can work even when one tire is up in the air with no traction at all. With the manual locking differential of our trucks, we engage the rear differential and it literally locks the two wheels together so they spin at the same rate. This comes in handy when going up slick boat ramps, or when off road and one tire might completely lose traction and just sit there and spin while the other tire does nothing. I've seen lots of trucks with a limited slip rear end get "stuck" on boat ramps because one tire loses traction causing the truck to not be able to make it up the boat ramp. If you will never leave pavement with your truck and never use it to launch a boat, I'd say go with the limited slip, but if your like me and an avid outdoorsman I'd go with the locker.
 

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It's a truck...get the 3.73 gears for towing, then buy a used Honda Accord with a 5 speed to get 40+MPG when your not hooked up to a trailer.
 

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I have a '13 FX4 and I was under the impression that the e-locker only works when 4x4 is engaged. I pulled the switch out when it was in 2 wheel drive and a light came on indicating that the e-locker was on. Can anyone clarify if it was indeed working or if 4x4 needs to be on?
 

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I have a '13 FX4 and I was under the impression that the e-locker only works when 4x4 is engaged. I pulled the switch out when it was in 2 wheel drive and a light came on indicating that the e-locker was on. Can anyone clarify if it was indeed working or if 4x4 needs to be on?
Don't think it matters. 4x4 or not.
 

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Also the elect locker not only works in 2wd but also up to 35mph rolling speed once your pass that rolling speed it will automatically disengage and them renegade once you drop back down below 30-35 mph. Really slick setup.
 

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The elocker can be engaged in 2 wheel drive mode on 4 wheel drive trucks after 2011 or 2012, I know for sure after 2011 as mine is a 2011 and I can't activate my elocker unless I'm in 4 wheel drive.
 

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The elocker can be engaged in 2 wheel drive mode on 4 wheel drive trucks after 2011 or 2012, I know for sure after 2011 as mine is a 2011 and I can't activate my elocker unless I'm in 4 wheel drive.
Viking- That is crazy and sorry to hear. I wonder if the dealership doesn't have a software patch or download that can allow the system to allow you to lock the read diff in 2wd.
 

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Viking- That is crazy and sorry to hear. I wonder if the dealership doesn't have a software patch or download that can allow the system to allow you to lock the read diff in 2wd.
I'm wondering the same thing, I think I'm going to call them and ask, there is no reason why you shouldn't be able to lock your diff in 2 wheel when you don't need 4 wheel but still want to get through a tight spot.
 
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