Hi All! Long time reader first time poster. I have been a GMT400 enthusiast for years and have one that is completely stumped me. I have put a new clutch and rebuilt the engine on my 1988 K1500 replaced the u-joints. I drained and filled the differential gears looked good and replaced brakes and drums due to wheel cylinder leaking and replaced seal on axle right rear side. After getting through testing and tuning I have a noise from rear of truck that I can feel in seat and transmission shifter. Here are symptoms as follows. In forward gears I feel and hear a noise that best described as whomp whomp at take off. Maybe even a binding feeling slightly. At first I thought I had left bolts loose on transmission to engine. Torqued those. Went through all bolts under truck and made sure that nothing was loose. changed transmission oil. (shifts better) shook the driveline and regreased u-joints no change. I thought it was like the springs loading up and rubbing together but can't seem to see anything that is the smoking gun. Any ideas would be awesome.
Noise AND vibration. Not just noise. And mostly at low speed? There's two dozen things this could be. I'd be looking at: Bent axle shaft(s) or bent wheel(s) (wobbling wheels) Worn output shaft bushing in transfer case output housing. Incorrectly-installed u-joints Missing trans-to-engine dowel pin(s) Distorted/warped brake drum(s) or rotor(s) Missing/broken exhaust hanger, weak/corroded pipe--exhaust system banging against something on takeoff. Broken leaf spring, failed bushings on trailing arms.
Thanks for the info it vibrates at speeds around 65-70. Sounds like my old 203 transfer case when the chain was loose
Fought that twice on my Trailblazer. Vibrated starting about 68 mph, worst about 72--73, and done by 80, First time was a wiped-out rear U-joint on the rear driveshaft. Second time was a bent rear driveshaft.
So I finally figured out what I was hearing. I jacked it up and checked everything out. I kept thinking the worst in my mind but decided to pull driveline out and roll it on flat surface and check newly installed u-joints. Driveline rolled perfectly. One of the issues I do have with the u-joints is no matter how I clocked them I can't get a grease gun on them unless I remove driveline. Even then it is tough. So I greased them until I used about a tube of grease and got enough in that every cap was pushing grease out. I reinstalled and drove. No noise. Solved. I guess the KISS diagnosis is the way to go. Thanks for help!
You have probably ruined the U-joints by driving with them not having proper lube. I guess you'll find out if the noise comes back.
Thats what I figured. I am going to try and find a u-joint that has a better greasing option as the ones I have I can't get my gun on.
The "best" U-joints are greased during installation, and have no provision for greasing afterwards. If you insist on greasing them in-service, get a proper grease needle to poke into the zerk. https://www.amazon.com/Performance-...=needle+grease+fitting&qid=1612230937&sr=8-12
