Wondering if anyone could clarify something about the rear end gears. 12 bolts means it's a 9-1/4 gearset, 10 bolts means 8-1/4 gearset. On my 2001 Durango R/T I have 10 bolts and 3.92 gears. I thought the bolt pattern always correlated to the gear so 10 bolts = 3.92, but I just read that isn't always the case.

Reason I am asking is because I am looking at swapping in a 2003 R/T rear end (with tow package) so I can have disc brakes in the rear of my 2001. I thought if an R/T came with a tow package from factory that mean't 3.92. 3.92 are the strongest gears for towing. I guess some of my confusion lies in understanding the difference between 8 1/4 gear set and 3.92 gears? Did 9-1/4 come with 3.92 gears? Anyway to tell if you can't make out the little metal tag?

 

Generate build sheets using your VIN and one from the donor vehicle, if you have it. My 03' Dak has the tow pkg with rear discs. Build sheet says....

Corporate 9.25 LD Rear Axle
3.55 Rear Axle Ratio

 

Number of bolts on the cover determines the size of the ring gear, not gear ratio. The same rear diff can have a multitude of different ratios, just depends on how it was optioned out.

 

Thanks dodgevity, the build sheet doesn't always generate the sale info. On my 2001 RT, the build sheet doesn't have the info. On my 2000, it does.

Ahhh i see. Guest the next question is, if the 2003 RT has the 12 bolt 9-1/4 and 3.92 gears, will that work for my 2001 that is 10 bolt and 8-1/4 with 3.92 gears for the swap? I know for sure i need the front and rear gears to be the same but not sure if the "ring gear" size matters. Both trucks are awd.

 

This is one of those cases where 'size doesn't matter'. If all the mount points, and sensors are the same, they will swap. I don't know if there are going to be differences in driveshafts, or things of that nature though. If you have to, could always get a hybrid u-joint to fit the larger rear diff.

 

will swap right in. whether "10 bolt" or 12 bolt" cover...… as long as it comes from a 98-03 Durango.
instead of counting bolts just compare the shape of the cover, quicker way of ID.... 9-1/4" model has "stop sign" shape cover, 8-1/4 is more oval.
how much would you be towing? Many many Dodge pickups and vans from the 70s-up had both model rear ends and did ALOT of towing in the day..... (no, a rear end from a 70s pickup wont bolt in, different housing length, spring perch spacing) but yeah the 9-1/4 model is a little more heavy duty.

 

I'll be towing a car trailer with a car and occasionally and my mini excavator as well (under 4k).

@HeyYou so as long as the gears are the same (3.92), I shouldn't have a problem with swapping to a larger 9-1/4 axle? Since the truck is AWD I def don't want to make a mistake.

So I just remembered this, the gears are also noted inside the glove compartment (this is the case for 2001 RTs at least)

 

Yep, front and rear gear ratio need to match. That is the most important thing.