clovehitch

First post on PT.net, hope I am putting this in the right place.

Current truck is a 2012 6.2 GMC Sierra, Black, 66k miles, 4x4, 3.42, ECSB, 2" level, ARH SS LT's, 3.5" SS MBRP, TSP VVT-3 cam at 40k, 3000Yank, BlackRhino Everest Wheels, 295/55R20 Toyo Open Country (yeah those tires aren't made for racing), 410rwhp, 400tq.

Possible transfer case problem?

I have been driving with this issue for a year and a half (it hasn't bothered me that much). It occurred after this 4x4 launch:

https://youtu.be/akSAHOX63z8

This is the only 4x4 launch I've ever done. Ever since this launch, when my stall is locked while cruising at around 43-55ishmph (1000-1500ish RPM), if I let off the pedal, there is a small clunking sound. Constant throttle means everything is smooth, and the problem is non-existent when the verter is unlocked. It's only when I'm cruising without cruise control, verter locked, and around this range (anywhere near 45mph) and slightly touching the throttle on and off to maintain speed. I don't know much about the transfer cases, but I think it may be a stretched chain. Am I crazy for thinking this? I cannot spin the driveshaft to save my life; it is solid. Any advice would be much appreciated. Thanks
-Dave

Wolftrk99

iTrader: (5)

Which transfer case do you have to begin with?

clovehitch

After 5 minutes of searching online (lol), I believe it is a borg warner, with the marking 8551223801 and F3 on the rear side. Like I said, I don't know much about these aside from what they do.

Here is a picture:

FFDP

iTrader: (2)

I'd try greasing the splines on the driveshaft.

I had a issue like that in my 2006 sierra and greasing the splines worked for me.

Wolftrk99

iTrader: (5)

There was actually a tsb for a driveline clunk, which the fix was greasing the yoke.... Easiest way to tell which transfer case you have is to look at the rpo label in the glove box, should be ngh, npo, nqf, and i believe there are a couple others...

clovehitch

I was under the impression that that clunk issue was mainly when you shifted into gear and during certain gear shifts (like the 1-2). I looked into it some around 2 years ago, before the launch, because I had a clunk which turned out to be part of the t-case not being bolted down well (bolt was loose). Very odd but I tightened it and it fixed the clunk completely (clunked on 1-2 shift and going into gear).

Wouldn't it be a freak thing if the groves within the spline connection of the shaft were worn? I BABY this truck for the most part, it's got almost all highway miles. I regret doing my only 4x4 launch too. Crazy since some people make 600 wheel and are ok after 100+ 4x4 launches (read that on this site before).

Pardon my ignorance on some of this.

HERE IS A VIDEO... LISTEN CLOSELY.
Clunk noises around 0:02, 0:08, 0:10, and around 0:11-0:12. I am purposely causing it to make the noise. Whatever it is, one 4x4 launch caused it.

https://youtu.be/Yu6_IyszxpY

Wolftrk99

iTrader: (5)

Link to the video isnt working.... There have been issues with the splines between the trans output and transfer case input being damaged....

clovehitch

That is a shame. And shame on me for doing a launch lol. I feel like most guys that cam a truck want to do at least one good 0-60.

So far, it works, so I may just leave it alone for a while and one day down the road do an AWD swap (well, have a reputable shop do it).

The other link works fine for me, but here's the link pasted straight from the desktop version of YouTube (I'm on a phone).

https://www.youtube.com/watch?v=Yu6_IyszxpY

Wolftrk99

iTrader: (5)

The problem there is no lubrication between the t case and transfer case so splines are dry, may need to pull transfer case and lube the splines. Have you checked the u joints by chance?

clovehitch

U-joints are good. GM advises against putting grease there on the 4wd trucks I'm pretty sure, as grease can get into the ATF and eventually cause transmission failure.

I don't understand how it could be lubricated before a launch and not lubricated after.... The difference was night and day, although the clunk is not terribly loud. Nothing one second, permanent clunk the next.