Strange "clunking" noise in my drivetrain...

[Hydengr]

Ok folks, first the background...

I'm the original owner of the truck. It has 145K miles on it. It is garage kept and in very good condition. Never "abused". Stock other than the mods in my sig, below. Tires are 235-85-16 BFGs.

Few weeks ago, I had the rear transfer case output shaft oil seal replaced by a local shop. When I picked it up, I noticed a clunk, clunk, clunk that persisted for maybe 30 seconds while I traveled maybe 200 yards. After that time, the noise disappeared completely. For the last few weeks, I will hear this sound when the truck is first driven, but only if it has sat for 4 hours or so. If I run an errand, park the truck, then get back into it an hour or so later, the sound is not there.

My "only" thought is that it might be a bad U-joint but I'm at a loss as to how/why the sound is so short lived. U-joints are original. I crawled underneath and verified that the bolts on the U-joint are tight. The mechanic also marked and re-installed the driveshaft to match his index mark.

The noise does appear to be speed sensitive, but it doesn't matter if I brake or I'm in gear, or coasting in neutral. I even put the transfer case into neutral but that too had zero impact. No issues with 4wd as I used it several times after the seal was replaced.

IMO, the crazy thing is that after the approx. 30 seconds, 200 yards, the noise is gone until the next time that the truck has sat for 4 hours or so.

I'm open to your thoughts/suggestions.

Thanks in advance.

 

[c1500deathtrap]

Drop the driveshaft from the transmission and run it. then you will at least you will know if it is in the engine/xmsn or the driveshaft/rear end.

 

[skylark]

Grease the splines of the transfer case. This is reasonably common. I help out a buddy with a tranny shop when he gets backed up and we put a little bit of transdel, a tranny assembly grease on the splines for just that reason.

 

[DerekTheGreat]

Totally off topic here but I read your signature and that is a sweet truck! Take it you custom ordered it that way? Two-tone? Power windows & such? Does it have rear defrost? I'd keep that forever.

 

[Hydengr]

Folks,

Thanks for your replies!

c1500deathtrap: pulling the rear driveshaft would definitely tell me whether the problem was there or somewhere else, thanks.

skylark: I think you've nailed it. I'm going to go back to the shop and run this by them when I get a chance. I should just do it myself, but as I get older my hands just don't work as they should and even a minor job seems to morf into a cluster. This is why I took it to the "pros" in the first place... I'll definitely keep ya posted. BTW, I've read many of your posts in the past and you're a wealth of info with regards to these trucks. Thanks!

DerekTheGreat: Yep... Ordered the truck back in December of "95". Took delivery on 2 Feb 96. It's Victory Red w/ a Grey Cloth interior. Silverado Package gave me the PW, PDL, etc. Auto trans was automatically included with the Silverado Package but could be deleted, therefore giving me the NV3500 5spd and a credit of $1,250! Opted for the rear window defrost since I knew of several friends who had rear sliders but never used them since they couldn't be reached while driving. Been a great truck and no, it's not going anywhere other than MY garage, Thanks.​

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