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Old 03-27-2012, 02:33 PM   #1
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Default 3.15 rear end

Am I the only one that got 3.15's rear end gears from the factory? I absolutely love my truck. My only complaint was that it came stock with 3.15 gears. When I bought it, it had everything I wanted except the gears. I told myself not to pass up the truck only because of the rear end. I could always change the gears. However, I never hear of anyone mentioning that they have this ratio.

If you do have them, what do you think of them? Hate them? Love them? What gear have you or will you change them for?
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Old 03-27-2012, 03:41 PM   #2
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Originally Posted by PRNDL View Post
Am I the only one that got 3.15's rear end gears from the factory? I absolutely love my truck. My only complaint was that it came stock with 3.15 gears. When I bought it, it had everything I wanted except the gears. I told myself not to pass up the truck only because of the rear end. I could always change the gears. However, I never hear of anyone mentioning that they have this ratio.

If you do have them, what do you think of them? Hate them? Love them? What gear have you or will you change them for?
I've seen mention of this ratio before, but not as common as the others. Towing won't be as great as the 3.55s or 3.73s, but cruising on the highway will be better than the others. I'm guessing your truck doesn't have one of the towing packages, which is why it has that ratio. Could be wrong though, just doesn't make since to me they would put a 3.15 ratio in a truck that would do a good deal of towing. The 3.15s in the F-150s are all about fuel mileage.
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Old 03-27-2012, 03:52 PM   #3
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I wouldn't worry about it... unless you were planning on putting 37" tires on there...
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Old 03-27-2012, 04:27 PM   #4
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I've got the 3.15 LSD with the standard tow package. I tow 3,000 lbs - 6,000 lbs fairly often and can't say I have any problem with the 3.15. It cruises great on the highway, holds its gear going up hills, and I'm one of those guys really happy with my mileage. While a guy with the 3.73 rear may beat me off the line I really don't care, my EB has plenty of acceleration and passing power, so I'm a happy "3.15er". Wouldn't trade it.
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Old 03-27-2012, 04:54 PM   #5
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Not sure if that gear ratio is associated with 4x2 trucks, but i've noticed that most of the trucks that either have the 3.15 or 3.31 gears are 4x2. But as said above, if u don't plan on putting huge tires on or doing a lot of heavy towing, I wouldn't worry about it.
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Old 03-27-2012, 04:58 PM   #6
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I've got the 3.15 LSD with the standard tow package. I tow 3,000 lbs - 6,000 lbs fairly often and can't say I have any problem with the 3.15. It cruises great on the highway, holds its gear going up hills, and I'm one of those guys really happy with my mileage. While a guy with the 3.73 rear may beat me off the line I really don't care, my EB has plenty of acceleration and passing power, so I'm a happy "3.15er". Wouldn't trade it.

you've got the eco though, that will make up for A LOT when it comes to being under-geared.

if I was goin eco, I'd be ok with the 3.15's, but on a 5.4 I dont think I'd want anything less than the 3.73's. maybe 3.55's on a 4x2 reg cab, but on a crew cab, no way.
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Old 03-27-2012, 05:05 PM   #7
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with the 6 speed transmission, even with 3.15 gears, 1st gear is still WAY lower than it would have been with a 3.73 geared 4-speed.......ever hear of a guy not being able to get the load moving because they had 3.73 gears and a 5.4 (less power)? I haven't....

I think the steep gears are a hold over from older transmissions and not needed any longer....that's my opinion. i mean, so what if you can't tow in 6th gear (which you probably still can jsut fine with the ecoboost) - now you lock out 6th and have a 5 speed - but get fantasic mileage unloaded...best of both worlds!

i still wish i had bought that fx2 with the 3.15 gears. would have been a killer highway cruiser and i wouldn't have given up much towing (my opinion)
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Old 03-27-2012, 05:06 PM   #8
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i have the 3.15 and i love it... second gear is a beast
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Old 03-27-2012, 05:44 PM   #9
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There are plenty of trucks out there and in this forum that are loaded up and pushed hard on a daily basis, or at least every once in a while, and require the more stout gearing available.

But I would wager most truck owners are over geared and over engined to satisfy other needs rather than those of daily requirements. There's a bunch of guys here who feel there that mpg gains are negligible and would rather have the lower gearing for towing and performance. For those that spend much of their time towing or playing hard, there would be no argument from me.

However, for daily driving and occasional towing/tasks, I truly believe there is an economic benefit of running the taller gears (smaller number). Read through the mpg threads and I think it's evident the 3.55 trucks are seeing better numbers on average than the 3.73 trucks, and I can only imagine the 3.31 and 3.15 gear ratios see even better daily returns. Throw in a few hard working days, and sure, those gears, or maybe a smaller engine may not return top notch economy or performance due to working that much harder. But they often get the job done just fine, and the rest of the time the respective owner reaps the benefits of dollars saved on initial purchase price and daily operational costs. Just my 2 cents.
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Old 03-27-2012, 07:44 PM   #10
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IMO, the 3.15/3.31 gears are so Ford can meet CAFE.

I've gone from 2.73 to 3.55 (88 5.0L) and 3.27 to 3.73s (99 4.6L) in a couple of Mustangs and saw very little loss in mileage as a result of the swaps. In my experience, what you gave up on highway mileage you got back on city mileage as long as you didn't have a lead foot. Those 2.73s in particular required more throttle to get the car going, even just driving normally.

If you are going to tow anything, I would consider the 3.55 gear the minimum. Ford has put in a very tall 6th gear so even running 3.73s is like having 3.08s 10 years ago when 4 speed transmissions were the norm. You're not really giving away much in terms of fuel economy, but the lower gearing (particularly with the EB, where so much of the torque is available at lower RPMs) helps keep the engine in its optimum power band without the transmission having to downshift for small grades, etc.

Any difference between 3.55 and 3.73 mileage wise is due to driving habits. There's only about a 90 rpm difference at any given speed between the two. I think you'd have to compare the 3.15 gears to the 3.73s to see a repeatable difference in fuel economy.
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