Does anybody know what the difference is between the 3.55 axle ratio and 3.55 limited slip axle ratio? I have NO idea what all that means. Is it worth the extra $285 or whatever it is? Thanks.

 

The answer is, "it depends." A limited slip differential does just what its name implies - if one wheel is spinning and the other has traction it uses clutches to keep the wheels at nearly the same speed - so if one tire has traction the power to that wheel with good traction keeps the truck going. Having a limited slip differential is probably 80% as effective as having four wheel drive. A limited slip differential makes a lot of difference in the traction you can get.

The down side to a limited slip differential is that as both wheels are semi "locked" at the same rotation the truck is slightly less stable when turning. The rear axle tends to not want to turn as well as an axle without limited slip. This is most noticeable in wet conditions.

I have had both types of setups and prefer the limited slip for practical reasons. However, in the South it is not common for dealers to get the limited slip axles unless there is a reason to have them on the truck (4WD, or in conjunction with a trailering / tow package)

My 2004 Lariat has the standard 3.55 axle. I think the 3.73 woudl liven up performance a little, probably at the expense of fuel economy. Car and Driver tested a 3.73 from 0 to 60 in 8.2 seconds. Other magazines with the 3.55 versions have been posting nearly 10 second times.

The higher the number in your ale ratio the faster the engine turns in relation to the wheel speed. The 3.55 gearing is pretty low (great for fuel economy). My truck loafs along at 75 miles per hour at slightly over 2,000 RPM getting 19 to 21.5 MPG on flat land.

 

I thought Lariats came standard with the 3.73?

 

"My truck loafs along at 75 miles per hour at slightly over 2,000 RPM getting 19 to 21.5 MPG on flat land."


Are you getting that kind of mileage out of your 04? That's pretty impressive.

 

Re: LTD slip differential

I highly recommend it. It is a very cheap advantage in low traction situations. How Stuff Works .com has some great information differentials and the differences between opon, locked, and ltd slip. Also, member here have given their own great explainations if you try a search.

 

Thayer,

As far as I know, 3.73 is a 4wd gear. I don't think its available on 2wd.

If this is wrong, someone let me know.

 

From what I make of the order guide, 3.55:1 gear is standdard on 4x2 Lariat with 3:73 being optional. 4x4 Lariats get 3.73 standard. LTD slip optional for either axle ratio.

 

sorry, but you're wrong. 3.73 is the rear differential. all F150s are rear wheel drive, so they all have this.

check out this thread. it's where i got all my questions answered

you may also want to read up on www.howstuffworks.com

it is an awesome site with lots of good info.

 

BrewMaster, you're standing too close to the petri dish.

 

i have no idea what that means. please explain.

 

I think there is some miscommunication here.

bewmaster, I don't believe J-150 was trying to say that the 3.73 gear was the one inside the 4wd transfer case, just that 3.73 was standard on the 4wd models and he thought 2wd 04 F-150's could not get the 3.73 gears. That is not correct according to the order guide I read. 3.55 standard for 2wd, 3.55LS optional, 3.73 open optional, 3.73Ls optional.

Was that any better?

 

I believe what Raoul, in his own special way, is trying to say is that you're are incorrect (as was I) about the standard axle ratios. According to the big bad a** brochure, the 3.55 is standard on 2wd Lariats, as someone already pointed out. The 3.73 is standard on 4X4, I just assumed everyone bought a 4X4, that's why I said what I said earlier.

 

Prior to 2004, the 3.73 gear was offered with four wheel drive vehicles (unless it was a Lightning etc...). Otherwise, it couldn't be ordered on a two wheel drive vehicle.
This is all J-150 was trying to say.

So, he was wrong but, your reasoning for why he was wrong, was wrong. Am I wrong?

A lot of things have changed with the new model and it is difficult for prior owners to 'help' the '04 buyers without a whole lot of misunderstanding that we never had a problem with here before.
Just as new '04 members are befuddled by an 2003 FX4/Lariat truck.

 

3.73 is an option for non-4X4 folks that want to tow a heavy trailer.

 

Man, talk about opening the barn door and letting the cows run away.
The original question was LS or not LS. Nothing was said about 3.73 vs 3.55, gas mileage or 4X4's. Someone with more knowledge than me should really try to answer BigJim's question. APT gave it a try, and I agree, the LS option simply allows both rear wheels to pull simultaneously rather than have one spin aimlessly while the other is stuck bearing all the load and not moving.