Front end clunks when my 420d backhoe is in 4 wheel drive

Check brake calipers, then check transfer case, U-joints, front differential, and wheel bearings.

your drive shaft is going bad check the joints on shaft for wear or looseness

front driveshaft joints worn, front ring/pinion gears or bearings worn, front locking mechinism faulty or binding. If you put the car in 4x4 and the car fails to move, as in neutral type feeling, then all your torque is going to the front, something is not locked in and its just spinning. Transfer case faulty....

check your front drive shafts

if your truck has cvaxels which is only if it is independent front end your cv axel is bad. if you have straight axel it sounds like you have a bad universil joint its right behind your hub where the brake system is check both sides

I have a 96 ford explorer that has a clunking sound when I pull out slowly . If I engage 4 wheel drive the clunking stops. I have replace the ball joints and right front axil and ground the breaks. Can anyone give me a suggestion. Sounds as if something is binding.

usually the noise in the front end is the u-joints or cv joints out towards the tires.

May be the locking hub. Do not drive this vehicle on dry pavement in four wheel drive.

sounds like a cv joint

the light is on.........let's see, where you having problems with clunking noises in the front, now or before when or not in 4 wheel drive? If so sounds like cv/axle shats/joints. Last time you used 4 wheel, was there a big clunk, just once? Is there an ocasional clunk when going over bumps? If so, sounds like Ujoint. I don't belive chevys use vaccum for 4 wheel drives systems at all.