hy guys i drive a supercrew 2006 fx4 with the 5.4lt with the 3.73 ratio. This few days ago i been hearing a noise on my truck from 40miles to 55 miles aprox, like a winning noise. I took the truck to the dealer and they told me it is my differential. Well i have to replaced it, so i want to get a 4:10 or 4:30. What do you guys think? should i stick with stock 3.73 or changed to 4:10 or 4:30 and i have no clue where to get it apreciated any help guys.

 

Dumb question I guess, but do you not have to change the front gears too? To match?

 

Remember Bluejay, no dumb questions. You do have to change the front diff gears too.

 

Yeah i know i have to changed the front too. So again let's go back to the questions what should i do apreciated guys any help.

 

Are you prepared to spend $1500? Do you have a need for lower gears? 3.73's are pretty decent to begin with if you have a 5.4. It's the 4.6 that needs all the help it can get, it needs higher RPM's to get it moving.

 

Bluejay, yes, you have to match the front to the rear, or never use 4WD again. otherwise, the transfer case will go POP if 4WD is engaged.

 

I upgraded my rearend when i had the whine(after I sank it in water)

I kept the same gears but replaced all bearings and seals and upgraded to a Detroit TrueTrac limited slip. Its awesome now and grabs hard. The whine is often caused by the pinion bearings wearing out or burning up due to oil displacement.

 

I would go with 4.10's if you plan to keep the tires right around the stock size. Would be a sweet new "umph" off the line.

** dif gears don't have to be the same, just close. I have seen guys run 5.12 up front in their rigs, and 5.38 out back.

Also, Ford, FOR YEARS, ran 3.50 front and 3.55 rear

Toyota did it on the 4runner for years as well.
Just some interesting facts.

 

MT, i know you are the expert here, but with all the added electronic control in today's trucks, and how sensitive the sensors are to trip, could even a SLIGHT difference in ratio cause a problem? I'm just asking, bud, that is what i have been taught. I know for certain that too much of a difference will, as you certainly do...

 

No 4.30 available for the front axle. 4.10's with stock tires would rock!! 4.10's should have been standard......or at least optional on an FX4.

Also the difference between a 3.50 and a 3.55 is minimal.....the truck would never know the difference. You could almost consider it two different names for the same gear. And the reason for the difference was simply economics and production runs. Since there were both 3.50 and 3.55 gear sets available for the axles, they just used whichever was available.

You could run different front and rear gear sets in your new truck and never have a problem......untill you shifted into 4x4. And by different, I mean something like 3.73 in the front and 4.56's in the back. And then, the only "problem" you would have.........is something would go BOOM!! But, electronically, the truck would never know.

 

I think that going from 3.73's to 4.10's wouldn't be much of a difference. If you're going to get new gears I say maybe think about 4.88's if you plan on getting some big tires in the future.

BUT if you HAVE to get new gears and you plan on staying with a relatively stock tire size, then I say 4.10's are the best all round gear out there.

 

Here is the defining question, what are you planning on using the truck for if you need to change the gear sets, what are your current tire/wheel size and/or are you planning to go larger. 3.73 are great set already, if you are planning to tow 5th wheel or go to tires with overall diameters of 33 then yea 4.10. If and when you do go larger tires and wheels might consider a brake upgrade.

 

Ya, I am sure something in the ABS might trip, if driving at higher speed in 4x4. Not sure it would throw any codes, might just not work as it should, thinking one end is "slipping" more then it should.

I was giving that info just as some "interesting facts" I thought I would share. Its something not a lot of people know, and many think you have to be within 1/100th or your truck goes *boom*. Not entirely true. You see it more on dedicated trail rigs.

 

that's what i figured, i've heard of that being done in trail rigs before... what is the primary reason though? unavailability of the same ratio for both axles? or there is some other hidden benefit?

 

If the ratios are off and/or the tires are not well matched, driving in 4wd on dry pavement can bind up the drivetrain. You need some slippage.