I replaced my leaf springs on my 99 4x4 Durango with 2001 durango leaf springs, which fit perfectly and measured out same as old, but it now has a significant vibration above 25 mph! I also changed both rear drive u joints as rig has 166k. Any thoughts would be appreciated!

 

did you also replace the shocks

 

I'd double check your U-joints.

 

X2 on U-joints. Get under there and muscle the **** out of everything under there to check for looseness. Check all the bushings.

 

id lean toward the ujoint as the issue also, it is going to be a rotating part that is causing the vibration.

 

I changed u joints after vibration occurred. Yoke axle is good too. New shocks 3 months ago. Wondering about shackles! I lowered vehicle before tightening shackles, or should that have been done without vehicle weight ? Are the springs off 01 Durango a problem for 99?

 

the springs shouldnt be the problem

52106325AB SPRING, Rear Leaf, [ZAR,ZNR] from the 98 parts manual
52106830AH 4x4 SPRING, Rear Leaf from 2001 parts manual
52106831AH 4x2 SPRING, Rear Leaf from 2001 parts manual

honestly if they measured the same they should fit just fine and not cause any problems.

 

is it possible that you have a wheel out of balance

 

I actually supported vehicle with jack stands on axle and run in place with wheels on and off, and of course road test and get the same vibration. When installing springs I felt like the axle had to til forward 1/4" to set flat on spring, but u joint should accommodate something that minor. I also did rear drum cylinders at same time as leaf springs but double checked that as well. Everything was normal before spring change

 

Wheel balance ok, new tires. This vibration is significant.