I have a 99 Blazer LS 4x4(NP8) and the Front Drive Shaft is worn badly..I have bought 2 from wreckers(same length) and replaced with new Universal Joints..problem is over 50 mph it vibrates bad..universal joint cups are in yoke properly..should I just have original rebuilt if possible..or keep looking..thanks in advance...Garv

Are you sure its the front driveshaft? It only gets loaded when in 4 wheel drive mode. Most of the time there's no stress. Why would it be so worn? If it's bent or out of balance you'll get a vibration. Try driving it without the front driveshaft in place and see if the vibration goes away.

Front driveshaft is always powered on 98up and 99up with Autotrac transfer cases have clutch vibration problems - need to change the fluid and use the GM blue Autotrak syn fluid and they have a bulletin on this - came about from the Bravada all wheeel drive cases (same as Blazer/Jimmy autotrac case) but no front axle unlock on them and theirs was getting all sorts of internal wear. That rear CV on the front driveshaft (between the transfer and front diff) is always a sloppy fit and if you grab it it does feel loose - I still do not understand why they used it instead of a u-joint, anyone really know?

Thanks Wirenut..have taken the shaft out and no vibration..I replaced the u-joint but it was a tight fit..do all the shafts take the same joint or is there different ones..maybe I got the wrong joint..shaft came from wreckers..and is suppose to be from 99 blazer...thanks again