weird chevy 1500 drive line noise

[bob442]

So i have this 1995 GM 1500, 4x4 5.7, 5 spd standard, with the aluminum drive shaft with plastic coating. not to long ago i replaced all the rear end seals due to leaks, the noise was there prior, but everything in the rear end was nice and tight and the original diff fluid was rather clean, This noise was there prior to the work, so just trying to make the problem make sence.
So, in any gear, except 1st, under load, with rpms between 1200-1500 (seems to cut out there 90% of the time) there is this horrible rattle coming form the rear of the truck(sounds like). You would think its a bad diff, because the noise is very simmilar to a bad coast noise on a front diff. this noise has progressively gotten louder, and i do not have the option of running it up on a hoiste. I'm thinking its the clutch or maybe just maybe the trans mount.

Also, anther weird issue is when trans is warm (30 min city driving usually) shifting into all gears is a bitch! checked the fluid, it was suggested to switch to a gear oil, but it calls for that GM syncromesh crap.

Feel free to share anyones similar experiances....

[19Cutlass94]

I have basically the same exact truck (Z71 v 4x4) and Im assuming you have the NV3500 5spd? I know the noise your talking about, except mine is more of a groaning noise than a rattle. Is the exhaust hitting anything? Like a tow hitch or a shock or anything? I had that happen and it made a rattling noise. Ive learned that on these tranny's under load they like to be above 1500rpm. Unless your cruising at light throttle, then it can stay under 1500rpm.

How bad is the shifting? Also what fluid are you using? DO NOT USE GEAR OIL! Youll ruin the synros and gears in a very short amount of time. Im running the royal purple syncromesh in there. When its cold you have to baby it a little bit, but when warm shifts fine. (Other than the bad syncros in the tranny that where like that when I bought the truck)

[bob442]

i just have the gm syncromesh in there and its clean, the cold shifts are great, its the warm shifts that suck, long highway pulls or city traffic bring up the problem. i'm thinking that its due to a warpped clutch or shitty clutch

[19Cutlass94]

Does the clutch slip at all? Thats strange that the cold shifts are better than the warm shifts. Its always the other way around... How does it act when shifting warm?

[bob442]

it wont pop into gear, kinda feels like the dogs are stacking up, or something is binding, or simply the gears wont "mesh" you know when a cable is fucked on a FWD car? thats how it feels, gotta smack it into the desired gear a few times. i'm less worried about that then the rattle drive train noise

[19Cutlass94]

Other than the sound can you feel anything in the drivetrain? If its coming from the rear all I can think of is maybe a ball fell out of a bearing, but that would have been very noticable if you checked the rear. And if its not howling its not a bearing.

Does this happen at a certain speed or strictly RPM?

[bob442]

Strickly RPM, but i've heard that the aluminum drive shafts with the plastic coating can resinate all sorts of problems. when the noise occurs, you can turn your head sideways, (ears front to back) and you hear it from the back (right ear, driving, turning your head right) it really just sounds like noisy gears, maybe a better way to discribe it is 'chattering gears' and as soon, As Soon as you coast or get over 1500 (seems to be a bit higher lately like 1800 RPM its gone completely. Its really stupid. When i can afford a clutch this spring i'll be changing it, unless it fails.

[19Cutlass94]

With the truck not moving and revving it does this happen? If the truck is neutral (the tranny is neutral) and the clutch engaged, does it make the sound then when revving? I would say its sounding like your clutch. Mine is fairly loud. I could probably get a sound clip of it for ya.

[bob442]

no mine is quiet in neutral, aside the exhaust leak lol

[19Cutlass94]

haha, i need new headers and y-pipe. I HATE dounut gaskets!!!

But I would tend to think either clutch or something in the tranny, especially if its that hard to get into any gear.

[bob442]

there is a nice SS set of heads on EBAY for 78$ well, a few sets, my flange area is just rotten

[60dgrzbelow0]

Bob...

This "Big Truck" forum seems like another good place to plumb their depths for some more answers. This particular link brings up some other possibilities for the cause of the noise and they all seem to point to recent changes in the kinds of replacement lubes as a possible culprit:

http://www.fullsizechevy.com/forum/general-discussion/technical-maintenance/201644-1995-chevy-z71-k1500-manual-transmission-noise.html