I have the 3.55 limited slip gear on my new Screw 5.4L and want to install the Daystar lift and put bigger tires. Anybody see an issue with this? Not sure of the tires size but 33 inches would be the max I can put anyway. I have been reading some previous threads saying the 3.73 would be better suited for this which I agree. But could there be a possible problem with gas mileage or being underpowered while towing a 19ft ski boat? Or possibly something even worse?

 

With a truck that has a stock tire of slightly less than 31", going to a 33" tire... you will notice slight "sluggishness" because of trying to turn larger tires.

Think of it like being in low gear on a bike (where one pedal makes the tire move one rotation) - then putting on a larger tire --- you're going to need to go to a higher (numerically) gear to still be able to turn the larger tire (where one pedal makes the tire move 3/4 of a rotation).

If you're planning on lifting your truck more later on, just leave the 3.55's, but if you plan on putting on 33's and stopping, go to a 3.92 (not sure if those sets are available for this axle) - or 4.10 don't waste your time doing a change from 3.55 to 3.73

 

What size tires do you have on it now?

If you are going fromt he 18 inch wheels to a 33 it's only an inch or so change. Even from the 17 inch wheels to 33's it would be a negligable change. Plus the Fords got plenty of low end torque to push a slightly bigger tire. It may be a touch more sluggish but I doubt you would hardly notice it...

As Vocabulaic said, I wouldn't change to just 3:73's. It wouldn't be worth it.

 

I have 255/70/17 on there right now.. And I plan on lifting the truck and putting bigger tires. Daystar lift with 33 or 35 for right now. Is it expensive to swap out the gears on a limited slip axle? Also do you know if both axles are limited slip or just the back?

 

Both front and rear axles are the same ratio as well correct?

 

They may be "slightly" off... like 4.11 front and 4.10 rear... however, I dont' think any of the big three are still doing that, so it should be exactly the same in the front as it is in the rear. Otherwise you would be tearing the CRAP out of your axles when in 4x4.

 

Do you know if all 4 wheels are limited slip or just the rear axle? I tried searching for this but can't find it in the manual. Don't even know if that matters in exchanging the gears.

 

Only the rear axle of the F-150 has the option of being a limited slip. The front is an open carrier.

Changing gears you should have no problems, unless you are going so deep (numerically high) that you are hitting the next carrier size. I do not know however, where the carrier split with these axles is.

 

Well whenever the time came I would only swap out to 4.10 gears I believe since from what I have read going from 3.55 to 3.73 would be a waste of money. I just don't want to hurt the MPG to bad but would like better performance when towing and offroading. Has anybody changed there gears? Or know how much the cost is to do that? I changed our the gears on my old truck for only a couple hundred bucks but I don't think I will touch this one myself. I guess just rear limited slip is better than nothing.

 

Gears should run you tops $400/axle parts & labour.

 

Thanks VOC.. Now I just need to find the money to go buy the stuff.

 

Hey do you guys know what kind of gearing 4 low goes too? I dropped it to 4 low and it clearly drops to another gearing. Do you know how fast can you drive the truck in this 4 low setting?