Squeal sound from 1-2 shift

[Moozery]

I've tried occasionally looking up on this for a while now but I haven't found anything that relates to what I'm experiencing.

Since I've switched from my 04 GT to my 04 GTP around April I've noticed that under moderate throttle (maybe 3500-4000 RPM area), right as the transmission gets ready to shift from 1st to 2nd there's this sound that lasts a second or two that sounds exactly like brake squeal. It starts just before the shift and continues until it's completed.

The transmission performs fine and the car is pretty low mileage, and I've done two pan drops since I've owned it and the last one I used Dex VI and it still occurs. I'm also using a TransGo shift kit.

Is this normal, and is there any explanation as to what this is?

[BillBooost37]

This is not normal. And not common, can't say I've heard of it before. That means it's just not one of the billion problems I had encountered.

Is there any way this might be a belt slipping?

[Gregorius]

Well, I think I've had this before. When I first got my '04 GT, it had 150k on it, and the tranny was misbehaving. It would drop hard into 1st sometimes when warm. 1-2 shifts were sluggish at best. 2-3 not much better. It was 2 years ago, but I remember a couple times a screaming sound on 1-2 shifts. Scary.

Shortly after I pulled the bastard into the garage and pulled the side cover off. Replaced both shift solenoids, the PCS and the TCC sol, and stuffed most of a Transgo kit in.

Total parts were less than $100 shipped from Amazon<ACDelco orig>. Drove it for another year or so, never heard the sound again and it shifted great.

[Moozery]

It seems pretty high pitched for a belt slip, but I do imagine the belts are getting pretty old.

I noticed today while using TapShift that I managed to make it happen a couple times while in 1st, although it wasn't during shift. Maybe it is actual brake squeal, which would be really odd though because other than this scenario they never make any noise.

[Transman304]

A failing 1-2 roller clutch also called a sprag will "squeal" as you described. The clutch is holding in 1st and 2nd and overrunning in other fwd gears.