4x4 causes vibration

[speedysprocket]

Hello,
Winter time and thus snow up here... So time to uses the 4 whel drive. Running in 4x4 is causing a vibration in the truck and it feels almost like the parking brake is on (something dragging). Every so often there will be a bang, then it smooths out for a little while. Shifting to 2wd doesn't cure the vibration immediatly. After driving for sometime, it will bang again, smooth out and the engine is less strained. It's an 85 Bronco II with a 5-speed and Warn hubs.
Any help or direction would be appreciated.
Thanks, Alex

 

[97ranger4x4]

Well lets start with the basics, To your Transfer case and front diff have fluid? I am guessing the vibration feels like it is from the front end? Try taking off the wheels and spinning the front driveshaft while in 2wd to make sure there is no binding. try spinning the front wheels to make sure there is nothing they are snagging on.

So this seems to happen all the time, in 4wd or 2wd?

 

[speedysprocket]

Fluid was done maybe 4 or 5 years ago, which might be 5000 miles at most with synthetic AmsOil, and maybe some Lucas. I thought it might be that the front and rear tires are different brands and ages, so the diameter is not exactly the same, but it still does this vibration on the snow, even with the wheels spinning...
Thanks for the quick reply.

 

[97ranger4x4]

yeh different diameter tires will screw it up pretty bad in 4wd. what size tires do you have at each corner?

 

[speedysprocket]

They are 30x9.5 at each corner, fronts are just newer. Even on slippery or slushy snow though, there should be enough slip to take care of the small size difference. What gets me is the bang that frees everything.

 

[97ranger4x4]

Ohh I thought you had say 29" on the front and 30 or 31s on the back. Yeh thats small enought that your fine. Yeh that bang is an issue that needs to be fixed right away.

So how often does this happen? Only when you put it into 4wd or did it happen once
?