This is for V10 Ex. I need to confirm my rear diff gear ratio -- bought the Ex with 4-inch lift and 35-in tires. The rear diff tag is gone but the front diff sticker shows 3.73. However I do not know if the previews owner had messed with the gearing.

Here's my plan to determine the gear ratio:
Place a mark at the bottom of the tire and make another mark on the bottom facing portion of the driveshaft. Then with the truck in neutral, and the parking brake off, roll the rear tire around 1 revolution. Count the number of times the driveshaft spins.

Questions:
1) Do I need both wheels off the ground or 1 wheel does the job to give me an accurate count?

2) If I'm going to upgrade, should I go with 4.10 or 4.30? Looking for the best fuel economy. Mostly city driving.

3) Whats the best brand to get the most bang for my buck?

4) Do I need to change the front diff gearing also?

 

You definitely need to do front and rear together. That is what holds most guys back, due to the cost... in the lower 48, I have seen advertisements for around $2000 to $2500 for full gear changes front and back, includes new gears, bearings and seals. Add $1000 to that for Alaska...

You will get different opinions here as to the gear choice. I have a V-10 Ex with 3.73's in WA state, and off the line it is a dog, and it has factory 267-75-16 tires. I also have my V-10 Ex here in AK with 4.30 factory gears. It is a rocket off the line (although the supercharger and Banks Headers and Exhaust helps too) That is with 235-85-16 snow tires, and I could smoke them any time I wanted too. I will soon have the new spring swap done, and Ill put my 35x12.5x16.5 BFG's from my F350 for this summer till I can get the 20's sandblasted and painted, then I'll probably run the 305x55x20" Toyo AT's. Once I have the 35's on the Ex, I'll let you know how the throttle response is off the line. Many here say if you're running 35's and the V-10, go with 4.56 or 4.88's as the transmission will appreciate slipping less. If you do alot of stop and go, the lower gears will actually help with mileage, since you are not slipping the trans so much..
Just my 2 cents.
Garry in AK

 

No need to check, they are the same as the front.

 

That would'be been my first assumption but I'm not certain if the previous owner messed with the gears when the lift and bigger tires were installed.

 

Most accurate way to check is pull the diff cover and count teeth on the pinion and the ring gear. Than take the ring gear teeth/the pinion gear teeth.

 

Thought about that as well but I just changed my rear diff fluid less than 500 miles ago and I don't want to waste that. Unfortunately I forgot to check the gear ratio.

 

Impossible, your 4wd won't work with different front/rear gearing.

 

Not entirely true, it will work, it will bind on hard pack though.


In the mud racing world, guys run diff gear ratios front to back to get the front tires to spin faster that the back to help how the rig runs down the track.

 

If he is unsure of the ratio then he does need to check it to verify. Just because they left the factory as 3.73's doesn't mean they still are. And once folks start wrenching around with things anything is possible, currently (since last June) my rig has 3.73 fronts and 4.88's in the rear.

Nothing is impossible, mismatched but close ratios might not be so obvious on loose surfaces in 4X4, and it's also possible the OP hasn't used 4X4. My truck hasn't been in 4X4 for a year now and we don't know where the OP is from or what kind of useage his EX sees. Once again checking will verify.
With a LS rear you should be able to jack up and put the rear on stands, mark the tire and shaft and count turns to get your ratio.

 

I rarely put the Ex on 4x4 mode.........probably 2 -3 times in the last 2 years due to heavy snow. So not enough use to feel the difference in gear ratio. But again what do I know it might be still a 3.73 in the rear -- seems slow off the line with the bigger tires.

 

You would know it if they were different ratios. You wouldn't even be able to sell it like that............unless you got sneaky and didn't say anything. Off road with 2 ratios is ridiculous and you would be asking to break something.

 

you want 4.88 gears with your 35" tires
that would give you the ultimate final drive ratio of 4.30

 

U do realize that alot of vehicles don't have matching gears from the factory. Like 4.10 in one end and 4.11 in the other. If they are within 10% of each other it's considered acceptable.

I ran 3.50 gears in the front of a van I had and 4.11s in the back. Only locked it in 4 wheel drive when I got stuck. Worked just fine.

 

4.10 and 4.11 are not even 10% apart. That's like saying my left foot is 1/2" longer so I can balance better on my left foot..........lol