More front axle questions

[DFrank]

So I thought I had found a used front axle rotor to rotor for $1100. Guy said it was a 4. 10, then he decided it was actually a 3. 73, which does me no good.



How can I tell by looking at an axle, what the drive ratio is?



My truck is an 03. One parts guy said I can only use one form an o3 or an 04. Is that true? What changed after 04. 5?



If I find one locally that I can look at, is there anything to look for or avoid? Or do I just insist on lower mileage and hope for the best.



Will I be able to tell if the ball joints are ok by feel? I assume they would not move a bit by hand, but have never had one apart to know.



It sure would suck to buy a used part for a grand and get one that is compromised.

 

[AH64ID]

You can use one from any 3rd or 4th gen, as long as the gears are the same. If you find a 4th gen one it has a higher GAWR and a tighter turning radius.



The only way to tell by looking at the axle is to count the teeth on the ring and pinion and divide. .



You can also tell by having someone hold one of the wheel flanges still, spin the other wheel flange1 time and count the number of times the pinion spins, mulitply by 2 and thats your ratio.

 

[macdaddy]

If you are able to spin the rotors, turn them and count how many times the pinion yoke turns. mark the rotor turn it one complete time.



If the pinion yoke spins 3. 7 times its a 3:73. 1. 4. 1 times and shes a 4:10. 1



Mac

 

[AH64ID]

If you are able to spin the rotors, turn them and count how many times the pinion yoke turns. mark the rotor turn it one complete time.



If the pinion yoke spins 3. 7 times its a 3:73. 1. 4. 1 times and shes a 4:10. 1



Mac

But you have to hold the other side still, and double. 3. 73's will spin the pinion 1. 86 times for evey rotation with the other side held. If you don't hold the other side still it may move a little and throw the math off.

 

[rscurtis]

You may want to re-check your math. One rotation on the rotor will spin the pinion at half the ratio, as the spider gears are walking on the stationary gear. The best way to determine the ratio is to turn one rotor two revolutions (while the other is stationary), and count how many rev's the pinion turned.

 

[macdaddy]

I tried this years ago while showing a friend of mine. The truck was a F-150 (mine) with a Ford 8. 8 and limited slip. I had installed 4:10. 1's on it.



I was reinstalling the left tire after repairing a flat. Rotating the tire and wheel one complete turn spun the driveshaft what I would call 4. 1 times. It definitely wasn't over eight times.



Mac

 

[AH64ID]

You may want to re-check your math. One rotation on the rotor will spin the pinion at half the ratio, as the spider gears are walking on the stationary gear. The best way to determine the ratio is to turn one rotor two revolutions (while the other is stationary), and count how many rev's the pinion turned.

Whoops, I was thinking about the ratio correct, just typed it wrong.

I tried this years ago while showing a friend of mine. The truck was a F-150 (mine) with a Ford 8. 8 and limited slip. I had installed 4:10. 1's on it.



I was reinstalling the left tire after repairing a flat. Rotating the tire and wheel one complete turn spun the driveshaft what I would call 4. 1 times. It definitely wasn't over eight times.



Mac

I had my math backwords. In the scenario you just mentioned it would spin 2. 05 times from spider gear action.

 

[DFrank]

I've heard form 2 differnt techs that i need to look only at 03-05. ll the ones available used are too high mileage to think I'll be getting good ball joints.

I'd love to know i can look at newer axles. Anyone else care to comment?

 

[macdaddy]

As long as its a AAM 9. 25 youll be good. I would replace the ball joints with either moog, or carlisle (spelling) anyway.



It's to bad your in Colorado. I have a killer shop that does all the thing you need.



Mac

 

[AH64ID]

I've heard form 2 differnt techs that i need to look only at 03-05. ll the ones available used are too high mileage to think I'll be getting good ball joints.



I'd love to know i can look at newer axles. Anyone else care to comment?

I have no clue why they are telling you this. The axle/frame/suspension was unchanged from 03-09, then just upgraded for 10. The 10+ axles will bolt up and the suspension locatoins are the same. . You may contact the lower control arm at full turn on a 10+, which is why the LCA's on the 10+ are different, same length, location, just smaller around.

 

[DFrank]

Thanks guys. I think i will keep looking for a newer one.