DenaliGuy93.

Hey everyone, been having an issue lately that has only arose after me doing preventative maintenance (go figure) hopefully someone can confirm what im unfortunately hypothesizing. Been creeping the forums for years, but first time posting a personal issue that has me stumped. Buckle up, this is going to be a long one. i’ll start off with the basics, 2002 GMC Sierra Denali 6.0L AWD. 254xxx KMS if this is posted in the wrong section i apologize and feel free to move it where it needs to be. a week ago, i replaced all 4 u-joints under the truck with quality spicer replacements (due to getting a small cyclic squeek under the truck when moving) (note: both front and rear driveshafts are ONE PIECE) after the successful replacement of the u-joints, the cyclic squeak has disappeared. Score. However right after the repair, i developed a horrible grinding /vibration sound in the floor when i slam on the brakes from higher speed. also have a slight vibration now when driving at certain speeds. Note that this noise/grinding/vibration was NEVER PRESENT for the 75,000kms ive owned the truck, before i did the u-joint replacement. never there until i replaced the u-joints. so like any rash human being, i took both driveshafts into a driveshaft shop to get them balanced thinking that was the cause. well the driveshaft shop successfully balanced both shafts and they double checked my u-joint install. Everything checked out and good to go. re-installed driveshafts and the noise/vibration is still present during hard braking and small driveline vibration at highway speed. I’ll start off by saying NO, please dont tell me its anything to do with the brake system. They were all replaced 6 months ago. All rotors, all pads, all slides properly lubed and all calipers checked for proper movement/seize. The vibration is NOT in the steering wheel or brake pedal when braking. And i never had an issued slamming on the brakes for the last 75,000 kms, never had a vibration or noise until i replaced the universals. so ive ruled that out. next is the wheel bearings. Ive jacked up both axles and checked for play on all 4 wheel bearings. Solid. Not a single MM of play to be had. so wheel bearings are out. which brings me to the death blow. this is what im unfortunately hypothesizing and im hoping someone can chime in. About a month ago i had a leaking rear output shaft seal on the NP149 transfer case (AWD), no big deal i thought. Bought new seal and installed. Good to go no more leaks. but when i installed my newly balanced driveshafts from the shop, i noticed the rear output shaft of the TC, i can push up and down quite a bit and minimally side to side. There is play there thats not normal. If i push the output shaft hard enough upwards i can get a “click” sound from inside the Tcase as well. i would say roughly 1/16-1/8” of play up and down with the shaft. This isnt normal is it? which is where ive drawn the conclusion that my new u-joints on the rear shaft have tightened the slop in the driveline. The grinding/ vibration when slamming on the brakes is from the slip yoke sliding into the transfer case with momentum of the harsh braking, and putting pressure/pushing on the worn output shaft busing/bearing of the TC, giving me the horrible vibration / grinding. Does this sound like i could be correct? It would make sense that the output shaft bushing or bearing is toast since that output shaft seal started leaking a month ago and i replaced it. but what doesnt make sense is why didnt i have this grinding/vibration with the old u-joints and out of balance drive shaft for the last 75,000 kms?? why was it quiet as a mouse and now new universals and a balanced shaft has brought out a hiding demon? anyways just looking for some input, probably need a TC rebuild from what i can decipher, but that can be quite pricey. Might get a used TC out of a wrecker. But any suggestions would be great! I believe ive located the issue but i’d like some others input. thanks everyone. -DenaliGuy93.