3406 making clanking sound

Check the fan area see if any pulleys are loose. Hopefully its external & not internal. Look around before you start truck again.

 

The next step is to see identify what is causing the sound. The best of the situation is at least your home. You probably need to let the shop take a look at it. I hope the best hopefully nothing serious. How many miles on the motor.

 

If it hasn't been it is time to have it looked at. The best situation is at least you are home & not having a major problem on the road with a load.

 

On my old 3406 the fan hub is bolted on with 4 bolts. The holes on the fan hub bracket are slotted (really long slots). Should just have to loosen off the 4 bolts a couple turns. On top of fan hub there should be a long threaded bolt that sits vertically. Should just have to turn the bolt and it will pull the fan hub up, which tightens the belts. May want to spray a little penetrating oil on the small bolt and take it easy on it as they are easy to twist apart. Also make sure the fan doesn't hit the shroud after you've tightened the belts.

 

Just a thought, if it's a tapping noise it could have dropped a valve, to be safe I would pull the valve covers to check before starting it again. If the piston catches that valve you could be in for a rebuild.

Also, spin the fan and see if it's contacting anything, check the shroud is not loose anywhere and contacting the fan.

 

release the tension from the fan clutch belts ad try to wiggle it (fan clutch) I had something similar to what you're describing and it was the fan clutch hub ball bearing.