Difference between Series 3 and Series 4 Dana 30 Carrier Question

[b.ri.smooth]

Hey all,

Weird question/situation here, looking for some advice.

TLDR: How do you tell the difference between a Dana 30 Series 3 and Series 4 carrier? From what I understand, it difference is in the mounting surface thickness. Anyone know the thickness of each?

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My 1968 bronco had the 4.10 gear option - its on the Marti report. I was told by the previous owner that the 4x4 does not work, and not to shift into it. He explained that whoever rebuilt the axle was not aware that it was 4.10/4.11 geared and put 3.54 gears in the front. The back has never been rebuilt from what I understand.

I am refurbishing the axle and looking to match the gears. I have confirmed it to be 3.54 gears in the front. If the guy who rebuilt this originally didn't know the correct gears to put in, I can't really trust that he installed it with the appropriate carrier. Is it possible that the 3.54 gears could be installed on a Series 4 carrier? How do I know if I have the right carrier if I am looking to put the correct 4.10 gears in it?

 

[Broncobowsher]

I don't have much experience with Dana 30 besides opening them up and looking at the pile of teeth in the bottom. But generally it isn't the thickness that determines the series, it is the offset. Being the ring gear is pretty much a fixed diameter, it is the pinion gear that gets larger as the gearing goes up and smaller as the gearing goes down. To some extent the thickness of the ring gear is what varies to allow this to happen. But there are limits. The pinion can only get so large before the teeth on the ring gear run into the bolts that hold the ring gear on. When this happens, the carrier has the flange offset over more. Going the other way, the pinion gets smaller and the teeth get further away from the carrier. At some point you realize how much really good steel is being used just as filler. That good steel could be saved by moving the carrier surface over. When you are building millions of differentials, that is a lot of money to be saved. Doesn't really cost anything to do either. So that is why it is done. If you think about it, there is no way a 3-series gear set with that larger pinion gear will fit on a 4-series carrier. But go the other way around and you can fit a 4-series gear set on a 3-series carrier in a couple of ways. One would be a ring gear spacer, the other would be a thick gear set.

Now there is one more option that can sometimes work. Hack the carrier shims. The ring gear side needs to be thinned out, maybe even cut a little deeper probably on the carrier. This artificially shifts the ring gear mating surface over. The non-ring gear side just gets a lot of shims. Like an extra quarter inch or better of shims. This can mess with axles as well. The cross that the shafts bottom out against in the carrier is shifted over as well. I've heard of this being done for some bastard installs, something like the rear limited slip from a Subaru installed in the IFS of a Nissan or something that shouldn't really happen. But makes no sense as new Dana carriers are (at least were) really cheap to buy new. And if they got a used ring and pinion it would be easy to just get the carrier with the ring gear already installed. Which is probably what you have.

 

[b.ri.smooth]

Ah ok. I think I understand. So since I found the 3 series ring gear in there (3.54), its safe to say that the carrier is a series 3 and must've been changed as well at the time of regearing, or else it wouldn't have fit.

I think I'll just buy a new series 4 carrier rather than jerry-rigging a fix. Thanks so much for the thorough explanation.