Hey I have a 91 w150 4 speed auto with a 318. I have this clanking sound comin from under the truck and it sounds like from the rear. Used to just make the noise around 30 - 40 but now even idling around base in gear. When I'm driving I put it in neutral rev the engine and it doesn't clank but as soon as its in drive it does. So naturally I think its the u joints but the rear drive shaft is solid but the front is got some play in it. I suspect its the front drive shaft and u joints but just want some opinions on it. The truck has the np 241 transfer case so the question is if I just take out the drive shaft it should be fine to drive till I have time and money to replace it.

 

I would think U-joints only clank when first going into gear, either reverse or forward until they take up excessive slack if worn out. The front drive shaft should only turn when in 4 wheel drive.

 

It makes this noise while driving in gear any gear. It also confuses me because its a sporadic sound not constant. Any help?

 

For your last question, yes you can take the front driveshaft out with no problems. I dont think the front shaft is causing your problems as it should not be spinning if you are not in 4wd.

 

It has to do with either the tranny, differential or drive shaft because I free rev it in neutral and it don't do it but as soon as your in gear it does.

 

Wether the front drive shaft turns or not when not in 4x4 will depend on what front axle you have. If it is a vacuum operated front axle engagement system or full time 4x4 the front drive shaft will turn in 2x4 and 4x4 mode. Even with these systems you can remove the front drive shaft.

Did you also check the front axle u-joints at each front wheel? Did you look over the rear drive shaft for any non rusted spots that don't match the surrounding area like when a balance weight falls off.

You say as soon as it is in gear it does it when moving. Does it do it in gear but not moving?

 

He says that he has the Np241. Wouldn't full time have the Np203 or was there a full time front axle with that had the np241?

 

The NP241 was the only transfer case used with all of the different front end engagement systems. Not to mention that with the age of these trucks, unless you are the original owner you can't be sure the truck is original equipment.

 

My truck has the vacuum lock auto hubs and I'm fairly sure the front drive shaft spins while driving even though its not engaged. It only makes this noise in gear while moving that's why I thought drive shafts and u joints.

 

I doubt the noise is coming from the front since you are telling us it only makes this noise under power and power or not that changes nothing up front. You might try jacking the rear tires off the ground with the truck in neutral and turn the rear tires to see if there is any play in the drive train. Listen to the pumpkin, the rear axle bearings, the u-joints and the transfer case while turning the tires first clockwise then counter clockwise.

Just for clarity, the vacuum system is an axle lock system and actually doesn't have auto lock hubs but uses the same hub system as full time 4 wheel drive.