Transfer case

[Jobeasle]

I have a 99 silverado z71 new body style I have been chasing a rattle from underneath for weeks now....I changed the universals and the pinion bearing because it had play in it and I still have a rattle...you only hear the rattle when your driving slow down a dirt road say around 8 to 9 mph....you have to let out the gas and have no pressure on the drive line down a hill and you can hear it....catch is when you have it in 4x4 there's no rattle only when it's in 2wd any help is much appreciated

[davester]

perhaps the forks in the transfer case are worn?  They do wear, even if you don't shift/use 4wd a lot.

[Jobeasle]

What's the forks? And how can you tell? It doesn't rattle when you have pressure on the drive line

[davester]

the shifting forks.  I suppose you might be able to locate the sound if you get all 4 wheels off the ground, start it and put it in drive to replicate the conditions to make the sound, and if you can hear it, then crawl underneath the truck and carefully probe with a mechanics stethoscope to see where the sound is coming from.

[Jobeasle]

We did that when we did the pinion bearings an it was quiet other than the rotors rattling...I had the tires off it because my Jack stands weren't high enough to keep the tires off the ground safely....I may have to try it again...what's weird is it only does it in 2wd... now the front drive shaft the u joints are still stock but they don't seem to be bad at all...there's a little play where the shaft goes into the transfer case but the rest is tight...on the back shaft the bushing and seal was replaced the first of this year Also...the truck seems to have to be in a higher gear with no pressure on it at slow speeds...when it shifts down no rattle 

Edited November 7, 2020 by Jobeasle
Added too it

[riverbanks]

Think it's worth having someone in the bed, listening?

[Jobeasle]

You know I haven't even thought about that...with it at slow speeds they might could hear it underneath...I know they couldn't on the high way but maybe the dirt road they can....I have mud graps on it so you can really hear it on the high way unless you come to a fast stop...I drive slow down a dirt to keep crap from slinging up and that's how I noticed it coming from under the truck

[riverbanks]

Two more ideas,are the leaf springs dirty?,try a hosing off,give a good look for a hair line crack in between u bolts,other,try e-brake a little when the sound is happening, finding the location of a sound, sometimes it travels,throws you off

[Jobeasle]

I keep the truck extremely clean I just had it painted and seems like everything is going wrong since then...it's just weird how it does it...it sounds like aluminum rattling to me that's y I changed the universals on the rear shaft