Heathicus

Alright, so I start my car in the dead of winter with remote start from the comfort of my warm home, right? Vroom, dat satisfaction of a nice grunted exhaust. Day starts off great. Cup of orange juice, a bagel with some cream cheese, some Babybel cheese, a bowl of cereal, and a little cat play time before hitting the daily grind.

I walk non-chalantly to Elora, the black GXP I just bought a few months ago. I stroke the steering wheel, get situated in her seat, put the key in, and put her in gear. All is normal. Until I just barely hit the gas and "BVRRR" sound for about 3/4 of a second. I thought surely my car is haunted and it's trying to enact buyer's remorse. I convinced myself that wasn't the case, so I then thought maybe the tires were stuck to ice and were breaking free but it didn't really sound like it did on the old Grand Prix.

So I go on with my day; it chugs along until quitting time when I'm exhausted. Thought maybe the paranormal had left my vehicle and all was well. Repeated the process, backed her out of the parking spot I almost got a citation for, put her in gear, and 3-5 mph, same "BVRRR" sound for 3/4 of a second. It was 50 degrees out, there was no ice anywhere as it melted and only occurs on that first time I start her and put her in gear when she's cold, or after a 15-20 minute stop at a friends house (happens every time she's cold, reproducible). The sound definitely comes from the engine bay, but it sounds as if it's right in the middle, I can't tell because the vehicle is moving, can't really pin it with a stethoscope. Issue 1.

Around that same time period, I found myself needing to stop at a stop light (imagine that). So I do. I get a shudder (no sound, just teeny bit of vibration), of about 7-8 Hz when it tries to downshift from 2nd gear to 1st at around 15 mph to 10 mph when braking only. Thought okay, what if I put it in neutral and stop from 2nd, 3rd, 4th. No problem there, braking without shuddering. So what about tap shift? Tried it, and I can downshift perfectly without shuddering. Happens cold or warm. I believe this to be a problem with the transmission but only in automatic drive mode (not tap shift), possibly related to number 1 with both sounds coming from first gear. It's like it is trying to shift to first, but can't decide when to do it. Issue 2.

I've searched and searched and I find cases of real rough shuddering like that of railroad tracks due to the torque converter (thanks GM for manufacturing HORRIBLE torque converters btw), vibrations from brakes, and so on, and this is not the case. I've eliminated as many variables as I could. No check engine codes either.

Can any of you help me out? It may be grounds for a warranty repair. For reference, it has 114,000 miles on the original trans with no idea how hard the original owner drove it.

Ill_Born_ss

From looking at your previous threads, you have verified fluid level and hopefully the colour/smell.
The symptoms you note are unfortunately kinda expected with these transmissions. That being said, it sounds like a valve body problem with possible material build-up on the PCS solenoid (pressure control solenoid)
If you do have warranty take full advantage of it now. At least get it documented and possibly a pan drop for inspection with a filter change. If you could be there and witness what they find/see during this (pics if possible). If they don`t want to help you then take the car when cold out and safely hammer the crap out of it in the area the shudder occurs and then call a tow truck to bring it to them. They may want to assist you from the get go but standard practice is the cannot fix it unless they can see/ show broken parts, its just policy.

Heathicus

Yeah about that...I'm only dropping the pan once, and I don't have the cash for a pan drop/inspection if broken parts are not found. If I drop the pan, I get it rebuilt. It's such a bear to do anything to the car's engine though because there's no room to work. Hell, I barely got my TBS on.

If I recall correctly, this is similar to the problem my 2000 Grand Prix had with the solenoid. So I put it off and eventually my 4th gear clutch hub shredded splines as well (not warrantied and not worth fixing).

And I would hammer it in the area the shudder occurs, but it only occurs on downshift when braking. I let off the brake and it's fine. Pressing harder on the brakes and it will shift down quicker but you can still tell. I can't figure out why it doesn't do it when shifting up to second. I may just have to wait until it blows.

Edit: Turns out I dialed around to a few of shops I've been to and can get a free diagnostic, woohoo. I'll document how it goes.

Heathicus

Well I had it diagnosed and the vibration I feel when I brake is probably the lazy Bilstein I have in the rear I didn't know was lazy, or a normal downshift and I'm just not used to it. The guys drove my car and said shifting was perfect.

The humming/buzzing I hear when I start is traction control self test. That makes sense because it only happens when I shift into drive/reverse the first time after I start it. I shifted into neutral and shut my engine off, started, shifted, and buzz. Did it every time. The other day it iced real nice outside and I was like hmm... VROOM!, and it made the same sound at exactly the same pitch/volume. That eases my mind quite a bit.

Now on to see if I have stock tranny or in fact an aftermarket. I was kinda taking a gamble when I bought it because it had no paperwork of maintenance or repairs. On a side note, does anyone know if the trim bars with the window squeegees are removable?

Heathicus

Well...Sad to say I had to have this tranny rebuilt. I got the rev and clunk issue. I was in cruise on the highway going 64 when ZZZ! Tach went to 5k then slammed into gear jerking me back into the seat. I've got the part that failed too. It bent horribly because 1) it had been rebuilt before 2) cheap parts and 3) not rated for engine power. I got it rebuilt with high quality parts and had every worn part replaced and a shift kit put in under my extended warranty (thanks Route 66).

On a side note: the material floating around inside the tranny plugged the stock transmission cooler causing it to run at 212º even on a 40 degree day. Installed an aftermarket cooler to the radiator to bypass the plugged cooler, and zip tied the lines to the plastic piece on the bottom of the front end, temps run no more than 175 on a 90º day. Runs great now. Traction control still buzzes with self test, but letting everyone considering a GXP purchase that

115000 miles = second transmission rebuild and that it could cost upwards of $3500 parts and labor.