3.54 vs 3.55 gears - same?

95-up Dana 30's: I'm seeing online (gears/axles for sale, specs, etc.) the two ratios being used interchangeably with no rhyme or reason. As far as I know, 3.54 tooth count is 46/13 and 3.55 is 39/11, so the two ratios do exist separately.

Can someone shed some light on this? Which one did the XJ's come with, and are they as interchangeable as they would appear?

from what i've read they are compatible its simply how the manufacturer lables them but there is no difference (i think its a rounding thing)

Another hour of poking around on the interwebs here leads me to believe that there really isn't a 3.55 ratio in a Dana 30, exactly. People use the all-inclusive term "3.55's" to refer to a 3.54-front and 3.55-rear combination. Something to do with the physical dimensions of the Dana 30 ring and pinion: the math rounds closer to 3.54 than 3.55 with the teeth-count combination that fits. So for the people who scratch their heads over a 3.54-down / 3.73-up carrier break while they believe to have 3.55's . . . it's really a 3.54, and should view carrier breaks as such.

If someone with a 3.54/3.55 Dana 30 wants to count teeth and chime in, that'd be awesome.

shoulda caught me on Sunday when I had the cover off *shrug* hit me up again in about 15K miles

3.54 IS 3.55, your splittin hairs.

xcm said:

3.54 IS 3.55, your splittin hairs.

Click to expand...

I'm an engineer, I split hairs for a living.

In that case, ive allways heard the magic number is 5%, if the axles are within 5% front to back, everything is fine...

The interchangeability of 3.54/3.55 isn't in question.

The question also is not: "does the math round closer to 3.54 or 3.55?"

The question is, was there ever a 3.55 ring and pinion set for Dana 30 - physically different from the 3.54 set; different teeth counts than the 3.54 and a different OE part number entirely?

I was running that and never had any issues in the dirt, never tried 4wheel on the pavement though

The answer is, there are numerous versions of the Dana 30, such as CJ-5-7-8 Jeeps, XJ/YJ/TJ/ZJ, WJ Grand Cherokee, Liberty IFS D30, the 1966 Ford Bronco D30, and also High Pinion vs. Low Pinion. Although the same model axle has been used for almost 25 years, there are numerous various in brakes, hubs, differential orientation, wheel bolt pattern, and width. So, as long as the gears fit the carrier, all is good.

3.5 is close enough, really. 4.09 front and 4.10 rear gears has been common with Ford 4x4's for 40 years or more.

Your tire overall height front to rear probably makes more difference that 3.55 to 3.54.

hawk_sixsix said:

The question is, was there ever a 3.55 ring and pinion set for Dana 30 - physically different from the 3.54 set; different teeth counts than the 3.54 and a different OE part number entirely?

Click to expand...

I think you need to call a gear manufacturer who makes "3.55s" and ask them what the teeth count is.
Then call the manufactures who make "3.54's" and ask them what their teeth count is.

Other then that, if I buy a set of gears, I check to see if the ratio is correct, but after that I do not write it down. I believe you will have a hard time trying to find that answer here. Who knows, you might get lucky.

As for anyone reading this in the future who wants to know if you can run them together. Yes, yes you can. I've heard the same thing as XCM, "ive allways heard the magic number is 5%, if the axles are within 5% front to back, everything is fine...".

Several responses here all continuing to address mixing 3.54 and 3.55 gears. All true, got it. 100% correct, but that's not the question. NorCalChris is trackin', and to that end:

Precision Gear - D30 Regular Rotation - 3.54 ratio - 46/13 tooth count
Precision Gear - D30 Reverse Rotation - 3.54 ratio - 46/13 tooth count

Motive Gear - D30 TJ style, short pinion - 3.55 ratio - 39/11 tooth count
Motive Gear - D30 Reverse Rotation - 3.54 ratio - 39/11 tooth count

That's not my typo; even a manufacturer calls the same ratio both 3.54 and 3.55. But more importantly there are two different ring/pinion sets out there: nevermind what ratio they are called, one has 46/13 teeth and one has 39/11 teeth.

Which brings me back to the start of this thread: which set did XJ's come with; which tooth count matches OE (see? this is an OEM Tech Discussion thread) . . . or was it both sets, being year/model dependent?

obsessive compulsive often ?

XJ D30 use 39/11 gears.