Holy **** that sounds bad....

I'd get someone to make the grinding noise to ensure its the trans and not the transfer case. Probably is the trans.

Perhaps you have a bad sprag or stuck checkball like you stated. I'd crack open the trans at this point.

 

Similar sound in a 4l60e from a toasted planetary gear.

4L60E Grinding, Crunching Feeling In Reverse - Hot Rod Forum : Hotrodders Bulletin Board

 

Yeah. The noise is truly horrible to hear. After speaking with a few transmission shops around here they all seem to be able to agree upon, if it's making grinding noises, its something internal that needs to be investigated. Either way, I'm so pinched for time right now I may not have any other option but to get it towed to one....always sumin...

 

Trucks been at trans shop for 4 weeks.

Trans been torn down. Found snap ring not fully seated. No other issues.

T case, snap rings were over stretched and not seating correctly, they replaced them. No other issues.

Trans was thrown on the trans dyno. Doesn't grind or make any noises.

It appears to be the t-case. They are saying there is an "HD" version of the transfer case and I may have the wrong input shaft? I know there is 2 different gm 246 transfer cases (actually bought both input shafts, because first one had too many teeth where it fits into the planetary). Is this the "HD" version they are speaking of?

And any idea why my t-case is still grinding...

 

part#: 19132978
and
part#: 19299088

At least for my application (2007 1500 Suburban - NNBS), these were both wrong input shafts. One had too many teeth to fit into the planetary gear and they both did not have the proper cut teeth on the inside (same side as pressed in bearing).

I ordered 2 input shafts that were supposed to work with the gm 246. The trans shop had a 246 core that was the "HD" version. 32 spline input shaft and a 6 planet. I had them swap those out with mine and everything works just fine.

Trans however, when I drove the truck home last night (20 miles) got to 230+ F on the cluster. Not sure if the sensor/cluster needs re calibrated for the 4l80e swap? or if it really got that hot.

I'm guessing it did though because the trans started to make what sounded like pump whine. It would when moving and at a stop when I put it in D. Doesnt whine in any other gears, and I dont recall hearing it prior to it getting up over 215 or something.