I'm looking to get a used front and rear diffs from a salvage yard but want to make sure the gear ratios are what they say they are before I buy them. How do you go about doing that on the rear? I know you're supposed to count the teeth or something - can someone elaborate?

What about a entire front IFS diff? How can you tell gear ratio - do you have to open it up to count too or is there another way?

thanks
John

 

If you think your axle gearing has not been changed since it left the factory, you can read and decode the "axle code" from your vehicle information plate.
If your differential has been removed so that you can see and count the teeth on the gears, you can divide the number of teeth on the ring gear by the number of teeth on the pinion gear to come up with their ratio. For example, 41/10 gives you a 4.10:1 gear ratio (the most common stock ratio).
To verify gear ratios w/ the diffs on the vehicle, there is the "spin and count" method:
For "open" diffs:

Block the tires at one end of the vehicle to keep it from rolling, and then jack up a tire on the other end.
Place the transmission in neutral and release the parking brake if you are checking the rear diff.
Spin the tire exactly TWO full revolutions while at the same time counting exactly how many revolutions the driveshaft spins (marking the driveshaft and tires beforehand will make it easier to count revolutions).
The number of revolutions the driveshaft spins is your gear ratio.
If it spins just over 4 times, then the ratio is probably 4.10; 4-1/3 = 4.30; 4-1/2 = 4.56; just under 5 = 4.88; 5-1/3 = 5.29, etc.

 

Several techniques listed below:
http://www.4crawler.com/4x4/4R_TechI...oDetermination

Often the gears themselves will be stamped with the tooth count or ratio as well.

 

very well put

 

aye yea i think i copied that off 4x4wire...I'm not quite that eloquent..usually speak in broken sentences

 

Wow - just going by color code would be great/easiest if the paint is still is on there.


So i guess on a front ifs differential - yuo need to "crack it open" to see the gears to be sure of the ratio, correct?

John

 

No, you can use the method dirtoyboy described above, just instead of turning the tire you turn one of the side shafts 2 revs and count the turns the pinion makes.

 

John, just an FYI....the color codes are not ALWAYS 100% correct from the factory...I have seen them mixed up. Always manually verify the ratio before buying, selling or installing