Im having some trouble with the rear end in my 95 ram 2500. From what I could gather, the rear end I should have is a dana 70 with 3.55 ratio. I ordered a rear end for this truck and it was slightly bigger and the brakes were different. When I switched it all over and put the rear end in, the four wheel drive no longer works, the speedometer is off and the front tires lock up. This means they sent me the incorrect rear end right? Im thinking the one they sent me was a dana 80 with 4.10 ratio. Is the dana 80 rear end bigger than the dana 70?
You can go to a larger axle physically but you do have to stay with the gear ratio that matches the front so the two drive shafts turn at the same speed. Look for a small metal tag under one of the differential cover bolts. The gear ratio will be stamped on it.
There is also a consideration with the brake size because that was carefully designed in with the size of the front brakes to create a balanced braking system front-to-rear. Look at the shoe width, lining length, and drum diameter first. If those are different the braking forces will be different. If they're the same you also must consider the diameter of the wheel cylinders. That affects how much force is put on the shoes. If you have rear-wheel anti-lock brakes, that will reduce easy rear-wheel lockup, but still, that is the type of thing insurance investigators and lawyers look for when they're trying to shift some of the blame for the crash from the other guy who ran the red light onto you.