How to figure out axle gearing at junk yard?
- Thread starter pELYgroso
- Start date
boogie_4wheel
Active Member
- Location
- North Salt Lake, Utah
ID tag on the axle (if it exists or is legible) will indicate gear ratio. Little metal tag near the differential cover.
Jack up one wheel (open diff) and count driveshaft turns to 1 tire. Driveshaft rotations times 2 = gear ratio. So if it took 1.8-1.9 drive shaft rotations to get the tire all the way around; 1.85 * 2 = 3.7 -> 3.73. This beats trying to get both tires up in the air.
Jack up one wheel (open diff) and count driveshaft turns to 1 tire. Driveshaft rotations times 2 = gear ratio. So if it took 1.8-1.9 drive shaft rotations to get the tire all the way around; 1.85 * 2 = 3.7 -> 3.73. This beats trying to get both tires up in the air.
- Location
- The Land Northward (Bountiful), Utah
I assume you're doing this for your cherokee. boogie is right on about counting, but in my experience I'm about 60-70% when I try it, and I've tried it a lot: like upwards of 40 times.
Most chrysler 8.25's have a tag and a printed sticker. Most dana axles should unless someone has been in the diff before and forgot to put it back on the cover bolt (so pretty much everything prior to 2000).
When in doubt always I count the ring and pinion.
Most chrysler 8.25's have a tag and a printed sticker. Most dana axles should unless someone has been in the diff before and forgot to put it back on the cover bolt (so pretty much everything prior to 2000).
When in doubt always I count the ring and pinion.
Spork
Tin Foil Hat Equipped
- Location
- Saratoga Springs, UT
And if you're like me and don't like math turn the wheel around twice instead of multiplying by 2.
- Location
- The Land Northward (Bountiful), Utah
Point is that it's difficult to count 3.7 rotations, if the pinion moves or if the other axleshaft moves at all it will throw your calculations out the window.
boogie_4wheel
Active Member
- Location
- North Salt Lake, Utah
Not that I go out junkyarding often, but take a paint pen or a silver sharpie, or even a soap stone. Mark the driveshaft and the pinion, mark the tire (to the fender or ground or whatever).
Or a few sockets and just pull the cover and roll it to find the stamp for the tooth count on the ring gear.
Or a few sockets and just pull the cover and roll it to find the stamp for the tooth count on the ring gear.
That whole math thing is just wrong. A gear ratio is *.**:1 None of this 1.8x2 stuff. Is that what they teach in schools these days?
3.75:1 is 3 and 3/4 revolutions of the driveline or input source for 1 whole revolution of the driven wheel. No exceptions or variables.
3.70, 3.73, 3.75, 3.79 as an example will all be 3-3/4 rev, knowing the application or family of the axle will split the hairs of exactly which ratio.
A 1st gear trans ratio of 6.69:1 means the engine will complete 6.69 revolutions when the trans output completes one.
A 2:1 low range in a transfer case means the trans output will complete 2 revolutions when the output completes one.
Trans Tcase diff
6.69 x 2 x 5.13 = 68.64:1 final drive ratio with trans in 1st and tcase in low range. The engine will complete 68.64 revolutions......... Am I redundant enough?
You can also divide ring teeth by pinion teeth to find ratio. This is the number you will most commonly see stamped in a ring gear. 41 11. SOOOOOO many people think this means 4.11:1 Wrong. 41/11 = 3.73:1 ratio
3.75:1 is 3 and 3/4 revolutions of the driveline or input source for 1 whole revolution of the driven wheel. No exceptions or variables.
3.70, 3.73, 3.75, 3.79 as an example will all be 3-3/4 rev, knowing the application or family of the axle will split the hairs of exactly which ratio.
A 1st gear trans ratio of 6.69:1 means the engine will complete 6.69 revolutions when the trans output completes one.
A 2:1 low range in a transfer case means the trans output will complete 2 revolutions when the output completes one.
Trans Tcase diff
6.69 x 2 x 5.13 = 68.64:1 final drive ratio with trans in 1st and tcase in low range. The engine will complete 68.64 revolutions......... Am I redundant enough?
You can also divide ring teeth by pinion teeth to find ratio. This is the number you will most commonly see stamped in a ring gear. 41 11. SOOOOOO many people think this means 4.11:1 Wrong. 41/11 = 3.73:1 ratio
The multiply by 2 is for if you have one wheel off the ground, not both--so you need to account for the spider gears in the differential doing their thing.