Is there any way to identify what a used D30 came off of? Also approx how many miles it had on it? I ask because I bought a used D30 from a guy who said it was off of a 2008 Jeep JK with only 5K miles. But it has a sticker on it with a number that begins with 2007. It also had 4.10 gears (which don't match my 3.73 rear).

Here are some pictures:

 

if it is a JK D30 with 4.10 gears, it came off an '07. part of the tow package in '07 was 4.10 gearing. in '08 (and since) the tow package had 3.73 gears. as for the mileage, no there is no way to determine that. just check the overal condition of it.

 

Yes I am. The mechanic told me he just looked at the tag on the replaced D30 which said 3.73 but when I tried 4WD I could tell something was wrong. A member here told me how to check using a simple chalk line/revolutions method and the front is 4.10 and the rear (which didn't get replaced) is 3.73. The mechanic has offered to put 4.10's in the rear for free but honestly I don't trust him anymore. I got suspicious when he tried to sell me front hub bearings for $259 each + labor. I don't think this was a honest mistake as he knows my kid goes offroad in this and I bet he was just waiting for an offroad trip so he could get more repairs. Either way, a future big bill was coming if anyone tried to go 4-wheeling with this gearing.

 

As far as the sway bar links - shouldn't those have come with my 2.5" terraflex coil lift kit?

 

It comes with rear links, then you move the stock rears up front. Hard to tell from the angle of that pic, but you want the swaybars to be level with the frame/ground, or pointing slightly upward.


Driving with different gearing front and rear is just an accident waiting to happen. If you are sure that they do not match, either take the mechanic up on the free install offer or find another shop and pay to have it done. And depending on tire size, it might be a good time to just go ahead and upgrade both.

And pull that front shaft off until you get the gearing taken care of.