Gear Ratio

[Bigglee]

Hey guys, I have a 2002 SD 7.3. I just got done installing an Icon Vehicle Dynamics 4.5 Hanger kit ( dual shocks in front, dual steering stabilizers ), MBRP 4 inch turbo back exhaust and an S&B intake system. I put 35 inch Toyo Open Country MT's on 20 inch XD Addicts (black). The truck looks awesome. It rides even better. Where I live, the roads are horrible, riddled with potholes from the winter. The truck is simply amazing whilst I bomb over the "terrain". It rides like a luxury vehicle. I couldn't be happier. If I wasn't so "computer-ly challenged", pics would be up!!! I'll try tomorrow.

My question is, ( I want a DP chip from Jody, so I want to have all the necessary info ready to go when I pick up the phone to place the order ). How can I find out what gear ratio came in the truck? Can I go to the local Ford dealership with the VIN number? Any help with this would be greatly appreciated. Thanks, Lee.

 

[mwessel]

You might look in the Wiki Articles, on the top right of the page. There is a section in there that should help.

 

[rammertide07]

Well I'm sure someone else will have a better method. I've done some research on it myself as I was curious as well. The easiest method I found online was jacking up the rear tires, put the truck in neutral, spin the tires. And the ratio is, I believe, for every revolution of the tires to the drive shaft (i.e. if the tire spins once and the shaft spins 2.5 times. So when the tires spin 4 times the shaft will turn 10 times...4:10 gearing). I beleive my math is correct.
But with your size tires you may want to consider getting new gears. You can check out powerstrokehelp.com. He has a video on the called "Big tires FUBAR transmission". There's lots of sites that has a new gear ratio calculator. I contacted them and asked if they suggested that I change my gear ratio with my tires. They said I should be fine with 4:10 gears.

Very interested to hear someone elses input on this so I can find out what my gear ratio is. I have no stamp on the diff. cover or anywhere else.

 

[Bigglee]

Checked the "Wiki" section, didn't find anything on gear ratio's.

 

[RoyBoy]

Should be a tag on a diff cover bolt with the ratio

 

[rammertide07]

Should be a tag on a diff cover bolt with the ratio

Is it possible that the factory bolt has been replaced and no-longer have the tag. I had it at a shop getting the fluids changed in the diff's and they could not find any numbers or tag.

 

[JLDickmon]

could call a dealer parts dept and give them the axle code off the door..

the problem with counting revolutions is it's not exact enough..
especially when you have multiple ratios close to one another, ie., 3.90, 4.10 & 4.35

so if unknown, best way would be to pop the cover and count teeth.. then divide the number of teeth on the ring gear by the number of teeth on the pinion

52 / 14 = 3.71:1

 

[rammertide07]

could call a dealer parts dept and give them the axle code off the door..

the problem with counting revolutions is it's not exact enough..
especially when you have multiple ratios close to one another, ie., 3.90, 4.10 & 4.35

so if unknown, best way would be to pop the cover and count teeth.. then divide the number of teeth on the ring gear by the number of teeth on the pinion

52 / 14 = 3.71:1

Yea, I thought about that before with some ratios being close together...just forgot to mention that. It wouldn't hurt to go ahead and chage the fluid if you haven't in a while and count the teeth while you're in there. That is the SUREST way to tell.

 

[Dogman]

So you know you can change the tire size and gear size with Jody's tuners so I go with the standard 3.73. Is your truck 4x4 if so look at the front cover for the tag.