Changing Axle Ratio

[southerland3044]

I have a 2002 Expo 5.4 EB 4x4 with 3.55 limited slip, and want to change it to a 4.10 . I am not looking to increase my towing capacity just get some help up the hills of East TN. Has anyone does this to their Expo and is it significant enough of a change to warrant the cost? I have been quoted $1400 to change both the front and the rear and an additional $250 for a programmer. Does this sound like a fair price? Thanks for any input!

 

[tonydiv]

I don't think that's too bad of a price. Are you running stock size rubber?

 

[southerland3044]

Yes, I have 17's stock, but will be putting 10 ply tires on when i change the ratio and begin towing.

 

[tonydiv]

There are quite a few tire/gear calculators on the web. I would go to one of those sites and enter in your old and new info to see where your rpms will end up when on the highway.

 

[TRTLSLO]

Price is about right. You will gain a few hundred RPM, lose a mpg or two with the gears, but should be able to make the mileage back with the programmer. You'll love the 4.10's, it should have been a factory option. 3.55's suck for towing, trans downshifts too much with em.

 

[mrford60]

the rpm shange is about 400rpm to each progressive change, you want to go up 2 ratios (3:73, 4:10) so your cruzing rpm would change about 800 rpms higher.

 

[Thermo]

Working the math, you will see about a 300 RPM change between the 3.55 gears and the 4.10 gears assuming stock tire size and traveling at 72 mph. So, you should now see about 2000 RPM when traveling at 70 mph with your current gears. After the gear change, you will be just a touch over 2300 RPM at 70 MPH.

If in doubt, get out on the highway, put the speedo at some speed, look at your RPMs really quickly (noting both numbers) and then find a gear ratio calculator on the net and plug in the numbers you get and then also inputting the new gear ratio. That will tell you down to the RPM

Starting with the stock numbers for my truck with 3.73 gears, I know at 72 MPH, the motor turns 2150 RPM, working the math:

Old RPM / old gear ratio = new RPM / new gear ratio, or

Old RPM x new gear ratio / old gear ratio = new RPM

2150 RPM x 3.55 / 3.73 = 2046 RPM

2150 RPM x 4.10 / 3.73 = 2363 RPM

Now, this all assumes that you make no other changes like new speed, different size tires, ect. Keep in mind that getting the motor above 2200 RPM pulls it out of its efficiency band. So, with the new gears, that somewhat "limits" you to 67 mph to keep your maximum mileage. If you are not too worried about mileage, then go balls to the wall.

 

[Canadian Expy]

Someone else posted this site when I changed gears, it works well
Gear Ratio Calculator

 

[southerland3044]

Thanks for the information! I am planning to do the gear change and also purchase an Edge programmer. From what I am reading I should pick up the difference in fuel mileage with the programmer right? I will be staying with stock size tires (17") and adding an additional trans cooler for insurance. Any other suggestions?