Backed the 4.9L 85 out of the garage today and heard a very loud high pitched scraping /grinding sound form the wheelhouse area. This happened when I put the car back in as well. Felt like the brakes were grabbing but put car on lift and all wheels spun freely. Only happens when car is put in D or R and gas pedal is pushed. Car struggles to move.
The sound is similar to a loud bearing squeal but it wasn't there when I rotated the wheels by hand. My guess is internal transmission problems, torque converter or even a cracked flex plate, but its a 60K mile transmission, (car has a 4T60e). A bit more checking is necessary before we pull it out for a rebuild, but has anyone experienced anything like this?

[This message has been edited by Dennis LaGrua (edited 07-05-2020).]

Is the noise close to a power steering pump noise/whine? As if a power steering pump is low on fluid. If so you could have a failing front pump in the transmission, sucking up air from the filter(if not all the way in) or even low on fluid. All would cause low system pressure. Which in turn will cause low clutch engagement.
Note: if it is from low fluid or sucking up air, it does not take long to wipe out the front pump.

quote Originally posted by cmechmann: Early 4T60s and 4t60Es could break strip out the "stove pipe assembly" clutch interlock tube/housing. However later rebuilds and later transmissions used beefier housings, along with better planetary gears. TH440 and very early 4T60 (the ones with non removable tail stock) had a habit of exploding the differential and breaking the case. 4T60e has an issue on very hard turns. The fluid sump lines are smaller diameter than the 4T65. And the is enough room on the left side of the case for air to be sucked in on very hard turns. All 4 series GM transmissions 4L and 4T are good at smoking clutch packs if the coolers are not in good shape. Even a partial restriction will burn them up These would be catastrophic failures that would show up while driving. If you have an issue when cold, it is more likely with a pump issue.

Thanks for the comments. The issue is when cold but with the scraping sound I don't want to take it on the road. Good idea, I will measure the pump pressure.
Update: Sounds more like the differential might have gone out. Any transmission guys here that have a good 4T60e to sell or want to rebuild mine? I rebuilt one with a friend 8 years ago and that one is still working for him. Cost only a few hundred to rebuild but you need to be very precise and need time. Time is tight, don't wish to tackle another but I might have to.
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[This message has been edited by Dennis LaGrua (edited 07-06-2020).]

Just a thought but could this problem be a fractured flex plate? As soon as the weather cools a bit we will pull down the powertrain.