vibration when hubs unlocked
 

:confused: I have been running my 70 k20 (79 fame) with no front drive shaft for the last two years to do away with the full time 4x4. I fainally got around to putting mile marker hubs and conversion kit in my 203 this winter. At first it worked fine, but the other day when i left home it started vibrating so bad that I couldn't drive over 30mph. So i pulled over checked everything visually, and it looked ok so i pulled back out on the road and it drove fine. Later that night it start vibrating again, but only over 60mph with the hubs unlocked. When i lock the hubs it doesn't vibrate anymore. I thought it was the front drive shaft, but im confused why it doesn't vibrate when the hubs are locked and the tcase is in 2wd. Any suggestions on where to start would be appreciated. Thank you!

vibration
 

Does it have a two piece rear shaft? Sounds like a carrier bearing or u joint Make sure u bolts on u joints are tight and in the center of the yolk

What is vibrating? Steering wheel?
How much is this really related to having the hubs in or out. If you turn them out will it start right up?

Problems like this aren't cut and dried. You are going to have to do some experimentation.

How are your front brake rotors? They all get warped and need to be turned now and then. The usuall cause is water splasing on a hot drum (I think). I have to do mine about every 3 years. If they are bad, you will get more vibration when braking. Turning in the hubs might just putting enough load on the axle to stabilize the asembly and stop the vibration.

Did you mess with the bearings in the hubs??

there really isn't much that could cause a vibration up front.

weights off the rims.
bearings loose.
balljoints bad.
a broke belt in a tire..

these are some to check if it happens with the hubs unlocked.

when I got my truck, if I put it in 4WD it would sound like a machine gun and rattle horribly, so bad that I couldn't drive at speeds over 25. turns out, the u joints on the front driveshaft were bad, causing the shaft to hit my exhaust pipe, and since it was offbalance it made the whole truck shake when in 4WD. maybe this helps?