NEED HELP: LS/Locker Gear Ratio Advice - FordTough.ca - Home of Canadian Ford Truck Enthusiasts
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post #1 of 20 (permalink) Old 04-22-2011, 10:02 AM Thread Starter
 
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LS/Locker Gear Ratio Advice

I've got an '04 5.4L 4X4 with 3.73 open diff and 34.5" Nitto Trail Grappler M/Ts.

Looking for suggestions on what gear ratio would give me the best highway fuel economy. Also wondering if I should look into a locker or limited slip for a bit of an off-roading edge.

I really have no idea where to start but my highway fuel economy really sucks! I'm also worried about the stress on my 4R75E tranny with my current gearing.

I've read alot of different opinions and still don't know which way I should go.

What do I need to buy to replace the gears? Can I do it myself? I do have the shop manual. If I go with a differential lock or Limited Slip, what do I need to buy? I'm assuming I'll need one for the front and rear each.

I really have no idea but the general concensus regarding gears for this tire size seems to be 4.56.

I'm gonna stop typing now because I'm just going to ramble on about how much I have no idea of what I'm talking about.

Any insight would be appreciated.
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post #2 of 20 (permalink) Old 04-22-2011, 01:47 PM
 
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Going from 3.73 to 4.56 would theoretically make your fuel mileage worse, not better. Basically, the higher the number the more torque.

My 2 cents -- unless you spend 99 percent of your time on the highway, with the gas pedal to the floor, then I don't think the axle ratio will make much difference to your mileage. It certainly wouldn't save you enough gas to justify the expense of replacing the ring gears in both your differentials. Remember, you'd have to change the ratio in your front diff, as well, to make it match. Gas might seem expensive right now, but it's not that expensive.

How about your tires? Those Nitto off-road tires probably have ton of rolling-resistance, compared to the run of the mill all-season radial tire. Install those on a full-size 4x4 with a big engine, and of course you're going to get worse mileage than a Toyota Echo.

Re: Lockers and LSDs
Lots of people here can tell you more about those first hand. You can install lockers and LSDs yourself. They don't change the gear ratio in your differential, as it uses the stock ring and pinion gears. You can install them in both front and rear diffs, if you're hardcore, but most people just put them on the rear, and that's pretty sufficient. I find with my stock LSD on the rear, quite often I don't even need to use 4x4 mode, whereas I probably would have, if I had an open diff.

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post #3 of 20 (permalink) Old 04-22-2011, 03:31 PM Thread Starter
 
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thanks for the input

i get an average of 25L/100 km now on the highway at about 120-125 km/h. It really is costing me a fortune to drive anywhere - even considering the only time I drive on the highway is to get off-road, it's very expensive. I'm going to try cutting the speed back to 80ish to see where that goes - it's going to take the life right out of me but maybe it'll allow me to actually drive it by saving me fuel. Also, I'm worried about the load on my tranny now due to my current gear ratio/tire size.

i just watched a vid hxxp://www.motorz.tv/blog/2668/ford-f150-gear-swap/ how to change the rear end gears.... whoa! it's a big job!!

I am a bit overwhelmed at the moment but I'd still like to know more... what's involved in changing the front gears, adding lockers or ls?

any suggestions of sites to look for parts?

thanks again!
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post #4 of 20 (permalink) Old 04-22-2011, 04:19 PM
 
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If you haven't corrected your speedo/odo you have no idea how fast you're going..or miles covered...4.56's are the recommended gear's for sure with 35's..it wouldn't be worthwhile for a swap to 4.10's, too small of a jump from the 3.73's you have now.

A good LS will help out alot in the off-roading dept, not as much as a locker. whatever you decide, do them both at the same time with the gears. Don't wanna get in there twice.

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post #5 of 20 (permalink) Old 04-22-2011, 04:49 PM Thread Starter
 
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yeah I got the dealer to adjust the PCM for the BFG 33.7" tires... I'm using 34.5" Nittos now so maybe I should get them to update it again. I want to get a Gryphon too...
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post #6 of 20 (permalink) Old 04-22-2011, 06:08 PM
 
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Definitely using a lighter foot on the skinny pedal will save you the most gas, and it doesn't cost a cent to do. I notice it big-time even on my little truck. Trucks are about as aerodynamic as a battleship, so the faster you go, the worse the fuel mileage. I used to be a speed demon, but once you get used to driving slower, it's pretty relaxed. Just put on the music, and sip some coffee. You'll get there a few minutes later, but you'll be safer and feel unstressed.

At the end of the day, though, good fuel mileage and having a trail vehicle are mutually exclusive, unless you build a Suzuki Samurai, or something.

Yeah, changing the gears front and back looks like a lengthy job. Putting in a locker or LSD on the rear isn't nearly so involved.

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post #7 of 20 (permalink) Old 04-22-2011, 11:13 PM
 
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i wouldnt change nothing, and if you have a 5.4 4x4 with 3.73s you have a stock LS, if its one wheel peal all the time just get a rebuild kit and do her up, i wouldnt do a gear change unless if you went over a 35s

i drove 60,000 and stock gears,and 37s its not to bad until you get into the deep stuff, 4low is used for that

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post #8 of 20 (permalink) Old 04-22-2011, 11:35 PM Thread Starter
 
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Quote:
Originally Posted by BIGPHIL View Post
i wouldnt change nothing, and if you have a 5.4 4x4 with 3.73s you have a stock LS.....
the code on the pillar under AXLE is 26. According to my shop manual, that means it's 3.73 non LS. B6 means 3.73 LS.

Thanks for your input though

whether or not I do the gears, the more I read about it, the more I'm leaning towards a locker instead of LS. At least starting with the rear end - probably an e-locker or air locker - something that works with push button and is reliable. I can only find one setup though and that's ARB and it seems to be ridiculously expensive.

I'm concerned with driveability with LS particularly in the winter - not so much for me but for the odd time my GF has to drive somewhere in it (I try to not let her drive it but it's inevitable sometimes). I dunno... maybe I shouldn't worry about that.

Last edited by SCrew Lariat; 04-23-2011 at 12:17 AM.
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post #9 of 20 (permalink) Old 04-23-2011, 01:42 AM
 
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Since the work installing a locker vs. installing an LSD is about the same (not too bad in either case), personally I'd go for an automatic locker, such as something made by Detroit, I think. A locker will be more effective than an LSD. There should be a lot of choices. An air actuated locker would mean you'd need to run a compressor, of course, so that's another complication.

I'd start looking into the relative merits of air/electric actuated lockers vs. automatic lockers. Sorry I don't know much more about it. You might also ask some questions about the drivability on pavement of automatic lockers compared to limited slip. I seem to recall reading that some the newer automatic lockers are pretty darn good as far as that goes.

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post #10 of 20 (permalink) Old 04-23-2011, 06:30 PM
 
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DONT do a full locker if ur only goin as big as a 35" and DD. eaton true track... a full locker on a dd is bad news bears.

You tried your best and you failed miserably. The lesson is 'never try'. -Homer Simpson
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