01 Dakota trying to find out what differential I have so I can get the gaskets to change. Any idea how to find out which rearend I have?? has the 5.9 automatic 4x4 and the front has the 3.55 gears, not sure if that helps.

 

for the rear diff it it is a 10 bolt it is a 8.25rear end or if it is a 12 bolt cover it is a 9.25(more likely to be the 9.25)

 

It should say on the glovebox decal. It's probably the Corporate 9.25" axle. Here's your axle guide:

http://coloradok5.com/axleguide.shtml

The 9.25" axle has a 12-bolt cover in an octagonal shape. The 8.25" axle has, I believe, a10-bolt cover. Even if it's 12 bolts, it's still round vs. the distinct octagonal shape of the 9.25".

 

There should be a sticker on the driver's side axle tube that has the size on it also. Assuming its not worn off. However, if you are talking about getting a diff cover gasket, OE uses silicone and thats what I would suggest using rather than getting an aftermarket gasket. A tube of black silicone works wonders

 

+1 on the black silicone. i just changed mine and it works great.

 

same here just did the service on my truck 3 weeks ago