I have a 87 f-150 2wd with the I6 and its also a automatic. My axle code is a 12 and im pretty sure that means its a 2.73 open differential, correct me if im wrong? I am wondering if gettin lower gears(i think that the right way to say it) would help me at all. Like 3.30s or something around there. Any suggestions would be appreciated.

 

Depends on what you want to do. The lower gears will lower you top speed, but will increase your acceleration and tow capacity. The larger gears should, I think, save some money if you drive on the highway alot. If you plan on getting larger tires then the smaller gears are almost a requirement. I have the 3.30 rearend with slightly larger tires (approx 1" larger diameter) and if I put even larger tires on it I think it would have the acceleration of a snail. So what do you want to do with your truck?

 

I would like some more acceleration from my truck. I am going to leave the stock size tires on and I dont do that much high-way driving. So what do you suggest is the best gears to go with?

 

My '88 F150 had a 3.08 rear end and 235/75-15 tires stock. The gearing was massively tall and it acted much better after I put 3.55 gears in it. This truck had a 5 speed manual (4 + overdrive).

My (new to me) '02 5.4 auto has 17" rims and a 3.31 rear. The gearing is too tall for normal driving and I'm looking at 3.73 gearing just to get it to drive normally. I'm only looking at about 500 rpm faster at 70 mph but around town will be much improved.

If you go as high as 4.10 then it will affect your highway top speed a bit (already an issue with the I6). I'd think 3.55 would be a good choice. Get someone who knows what they are doing to set it up. I did my own with no guidance and my pinion gears exploded after about 30K miles. You might also check junkyards for a rear axle with shorter gearing and just swap axles (with new fluid and brakes, of course).

 

3.55s sound like a good choice. So after I do this swap, what kind of differences should i see. A big difference or just something noticeable?

 

Much quicker accelleration, easier passing, better towing, easier to light up your tires on semi-slick surfaces (make sure there are no cops around), slightly higher engine rpm's at cruising speeds. You will need to get your speedometer recalibrated or else figure out what the difference is and keep it in mind when estimating your speed so you don't get tickets. The '87 should be just a matter of swapping out the plastic drive gear for the speedometer cable where it plugs into the transmission (I think).

Supposedly the taller gears are for better mileage, but I found that my mileage stayed the same or even increased since I wasn't lugging the engine as much. I think the taller gears are just less expensive for the manufacturer to use.

 

Thank you for your help. Its greatly appreciated!

 

My 92' had open 3:55, didn't like it much. I personally went to 4:10 anf added an auburn locker to boot and wouldn't trade it for anything. My mileage is about the same although with the 3:55's I always drove in 3rd. When I went to the 4:10's I started using the overdrive, so my mileage is a wash, whatever you do you will like it only once you get used to the new gears you may wish you had gone lower. Good luck

 

I just snagged some 3.73's from another local forum member here. He went to 4.56's on his 4WD and his old gears will fit on my 2WD F150. They only have about 4K miles on them. I'm going from 3.30 to 3.73 and I'm paying someone qualified to do the work so my rear axle doesn't grenade on me like my last one did.

 

Going from a weenie 2.73:1 to a 3.55:1 will make a dramatic difference is acceleration and towing capacity as stated.

While you're in there, toss in an LSD... I have an Eaton and it's superior to the Auburn as it's upgradable and rebuildable in the axle. A stock 31T Trac-Lok with 8 clutches and a new center preload spring would work rather nicely.

I went from a 3.55:1 to a 4.10:1 in my truck here in Jan or Feb... made a nice diff in acceleration. Tachs up about 400rpm higher on the freeway now so I'm around 2400rpm @ 70mph with 28" tires... I cruise around 65mph now due to the RPM diff.

Milage dropped maybe 1.5 on the freeway, I drove about 150mi to have it done... not enough to complain about. The truck is nice as it moves out of its way now.

 

I have 3.55 gears now and I am looking into 4.10's maybe 4.56's but probablly 4.10's I cant see the point in changign gears and not at least going with 3.73 gears. Ford hasnt doen any of us too many favors on motor sizing in the last 8 years or so. We wouldnt have to scrounge for gears if they would offer larger motors than the 4.6 and 5.4. They are pretty embarassing motors when you pull up beside another truck and it has a 350+ cubic inch motor. Unless your all mods.LOL

 

I have a 95 F150 4wd w/ 300 mazda 5 speed and 3.55 gears. I'm very pleased with mine, the gas mileage is pretty good as I get 15-16 city/highway combined. Although I have gotten up to 18 just on the highway. IMO ford should've never used anything but 3.55 as the minimum. I'm planning to switch 3.73 gears so I can tow better without straining my truck as much. If I ever get around to it I'm going to put an eaton unit as well.