77 FJ-40, 350, sm465, NP203 doubler, Toy T-case

Got a problem when I engage 4x4. A noise from the center of the rig makes a tapping sound that gets louder when you put a load on by using brakes. It varries with speed of rig. When in 4x4 going 25-30 mph on a road there is a vibration like a bad u-joint in the front drive line.

Took the front driveline off and both U-joints are OK no aparent problem with them. The output shaft from the T-case is ok as is the front diff. Drive line looks straight an no weights are missing.

Anything I am missing or should test?? Any idea what it might be?

Thx Dan

:blender:

Noises like the tapping, are often hard to figure out. To find out, put the truck up on 4 sturdy jack stands, put it in gear and rev it up until you hear the noise. Then get out and walk along the sides of the truch and listen for where the noise is coming from. Use a broom stick to pinpoint the noise. Ovbiously, you don't want to walk in front or get under a truck that is running and it would be good to have someone in the cab running the throttle. This might help you find out what is vibrating, but the usual drive shaft vibration problem is pinion flanges that are not parallel. Check the angles with an angle finder.

Had a similar situation, turned out to be the spring leaves shimmying, and raping against the C clamp restrainers. Jammed a piece of rubber between the leaves and clamps - rap was gone.