I've been checking into putting 3.55's in my axles, and some people are telling me that the front axle needs to be a 3.54 and the rear needs to be a 3.55. This does not sound right to me at all, but then again I'm pretty new to 4x4's. My D60 has the factory tag that says 4.10, but the rear axle is missing the tag and is NOT the original axle anyway. According to the folks I talked to, the rear ~should be a 4.11 with my current set up. They are telling me that it is for better steering handling, and that the front needs to turn a shade faster than the rear. I'm just having a hard time believing that this would not ruin the transmission and transfer case unless 4x4 was only used on an extremely soft surface, and if then, why would that small difference matter? This is just weird. Anyone care to clear this up for me? Common sense tells me to keep them exactly the same!

 

Ford traditionally geared their fronts and rears this way on a 4x4 so that the front wheels would turn *slightly* faster than the rears and this theoritically made the truck track straighter in loose off-road terrain.

 

Sorry, but this isn't the reason behind it at all.

It is a difference between the diff designs.. Dana vs Ford axles. Usually the ford axles have the "weird" gearing.

For example in the 9" you have 3.54, 4.11, 4.86, 5.14, 5.41... vs 3.55, 4.10, 4.88, 5.13, 5.38 in a D60. Exactly the same gears when it comes to matching them up.

Sterlings are the same in a few of the ratios. Has to do with ring gear/pinion diameters, positioning.. ect.

You can have up to a .05 difference and never know on hard pavement.

 

the 1/100's diffrence in the ratio will have no effect at all whatsoever. you run into issues if you try to pair a 3.55 with a 4.10, parts will not stay in their original locations very long.

 

I don't know anything about a 9", but my front D60 is 3.54, and my rear Ford (Sterling) is a 3.55

 

So I had one set backwards... shoot me :P

 

the diffrence comes from the size diffrence between the front and rear ring and pinion. my rear is a 3.55 with a 3.54 front. The Dana 60 is a 9.75'' dia ring with a 46 tooth ring/13 tooth pinion. that works out to 3.5384615 for the ratio, rounded to 3.54. the stearling rear is a 10.25 inch dia ring with a 39 tooth ring and a 11 tooth pinion. the ratio works out to 3.5454545, rounded to 3.55.

 

Thanks NMB2 and Country Boy, this is the only explanation that has made any sense... it still seems like that small difference would add up and create friction and strain on the tramsmission and transfer case, but it real life I'm sure differences in tire wear and pressure etc., are far greater than the tiny difference in ratio. I do see R&P sets for Dana 60 from drive train america in both 3.54 and 3.55 ratios, but maybe this is a difference between manufacturers. If I call them they can probably tell me what set is the closest for whatever rear axle I end up using. Thanks again guys!

 

Like I said... as long as you are within .05 of eachother you will never know the difference on dry pavement. I promise

 

remember that you will have loses through the drivetrain itself, no machine is 100% efficent, that small diffrence in ratio is negligible.

 

In theory wouldnt the ring gear have to have at least 100 teeth to actually change the ratio .010 at a time? Its the same ratio just called something different.

 

If they were both 3.55 or 4.11 you would push threw a corner rather than steer through it.

 

That would be true if the pinion tooth count couldn't change. By changing both the pinion and the ring gears, very small ratio changes can be made. See post #7 above...

 

With part time 4x4. You should only run it on wet surfaces where the wheels are allowed to naturally slip. This is the nature of the beast as we have no differential in the transfer case. The difference is negligible. But, don't use your 4x4 on dry pavement.

 

Right, this is why you feal binding when you try to turn in 4x4 on dry pavement. the front and rear driveshafts are trying to turn at a slightly diffrent speed. the old NP203 Full time cases in the older full time 4x4 solid axles used an interaxle differential in the case. this allowed the front and rear shafts to turn at a diffrent speed when turning.