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Posted By: NateB 93 G20 Vibration/Drone/Clunking Sound - March 19th 2020 11:40 am
I'm getting a drone/vibration at highway speeds and also when I let up off the accelerator I can hear a clunking/knocking sound from underneath right below the front seats.

A little history. I had the rear diff rebuilt with new everything...axle bearings/seals and a 3.73 Dana True-Trac posi kit. All checks out good back there. Also had new u-joints installed, but then had a catastrophic failure of one of the u-joints on the highway. Had the van towed back to the shop that replaced the u-joints, but the damage was so severe they had to have a new driveshaft made. I've had the driveshaft checked twice and it's in balance.

I'm at a loss here...u-joints are tight, rear diff is good, driveshaft is in balance, but I have a sneaking suspicion that the bearing/bushing in the trans tailshaft is shot. I do believe the trans mount is fine as I had that replaced a couple of years ago.

Thoughts?
Posted By: Astrocreep66 Re: 93 G20 Vibration/Drone/Clunking Sound - March 19th 2020 1:12 pm
Which van? Sounds like tail shaft, I would start at torque converter bolts and work my way back being that it seems to be making noise at front seat area.. just my thoughts.
Posted By: CatFish Re: 93 G20 Vibration/Drone/Clunking Sound - March 19th 2020 2:21 pm
Hey Nate!
You should check the tail shaft just to be sure but that may not be your problem.
The noise you're describing sounds like every True-Trac posi I've ever heard. They're known to snap/crackle/pop/clunk, especially at lower speeds and even going straight ahead. The hollow driveshaft transmits the sound to the front.

My2%.
Posted By: Astrocreep66 Re: 93 G20 Vibration/Drone/Clunking Sound - March 19th 2020 3:18 pm
My 73 has a posi and was doing all kinds of knocking and clunking, I tried the left ,right, left hard steer no different, I found a receipt from the shop that serviced it it had standard 80/90 in it, got a couple small bottles of friction modifier no more noise. And yeah what Catfish said.😁
Posted By: frscke1 Re: 93 G20 Vibration/Drone/Clunking Sound - March 19th 2020 5:32 pm
I hear N feel the same thing in my 92 with posi …. I was told its the clutch paks in the rear slippin when turning.
Posted By: CatFish Re: 93 G20 Vibration/Drone/Clunking Sound - March 20th 2020 1:54 am
Dana True-Trac is a planetary gear system, very tough. And they can be noisy when they lock and unlock as there is, of course, clearance in all those gears between the axles. Not a bad thing, just takes some getting used to.....
Posted By: NateB Re: 93 G20 Vibration/Drone/Clunking Sound - March 24th 2020 4:12 pm
Hmmmm. I'm running Amsoil synthetic lube 75W-140. Rear was rebuilt by a Jeep/4x4 specialty shop and that's the lube they use. Like Catfish said, no clutches but all gears. If that's the noise they make, then I'll live with it, but the vibration/drone has to be something different.
Posted By: NateB Re: 93 G20 Vibration/Drone/Clunking Sound - March 24th 2020 4:20 pm
I kinda wish now I would've had a stock rebuild done, but noooooooooo I had to get all fancy and sh*t. lol
Posted By: Astrocreep66 Re: 93 G20 Vibration/Drone/Clunking Sound - March 24th 2020 8:51 pm
I had a mini spool in my Astro.. count your blessings.lol
Posted By: Astrocreep66 Re: 93 G20 Vibration/Drone/Clunking Sound - March 24th 2020 8:52 pm
I had a mini spool in my Astro.. count your blessings.lol
Posted By: NateB Re: 93 G20 Vibration/Drone/Clunking Sound - June 15th 2020 2:13 pm
Well...the vibration/drone issue was my motor mounts. They weren't broken, just 30 years old and collapsed. I bought a set of GM OEM mounts and had them replaced along with the trans mount. All smooth now!
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