Transmission Issue- Grand Prix GTP

[Dncspencer]

I have a 1998 Grand Prix GTP
3.8 liter, series 2, supercharger, aftermarket air filter, 4t65ehd Transmission (hince why i'm in this topic lol)
I bought this car for my girlfriend it was a good price and I bought it from a friend figured it would be a rather simple fix in my garage.

When I got it, the car was reving between 5k-6k where the rev limiter kicks in.
Now the car wont shift, when you first start going, it will be okay in the drive gear, however; once you stop a few times, you have to put it in the manual 1st gear to take off and manually shift up however; it will not always go in to 2nd or 3rd and 4th is a rare occasion.

So my buddy and I after some research, jacked it up and repleaced the 1/2 and 3/4 shift control solenoids, put it back together topped it off with some new fluid as the old was complete BURNT. now the car at first was fine, but quickly went right back to its old ways it was reving and not shifting, my girlfriend however got frustrated, and went a head and nailed it to the floor to take off as it didn't even want to take off in 1st she got the hesitation at 6 k from the rev limitor and it started shifting fairly normal, however 4th is still not completely shifting, I am at a complete loss on what it could be, I don't want to just JUMP and change out the trans, she don't really have the money for that, she has a kid, but I don't want her to keep dumping money in to odd ball parts either. So if you could point me in a good direction to look, please dooo. I did eventually get 4th to shift, when I reved it and it shifted at 70mph.

Now I'm not sure if it is the original trans or not, the car reads 253k almost 254 but it runs like a champ, is just the shiftting, also if you know a good place to get a deccently priced after market trans if that is the answer that would be great too. Thank you

[Scottydoggs]

sounds like the tans is dead.

[Dncspencer]

it does still shift, just have to tack it up high, though i suppose it could still be done!

[dsmuts]

Sounds like your forward band broke.

[BillBoost37]

Sounds like your forward band broke.

How's that Danno?

OP:
4th gear not engaging is fairly common on higher mileage transmissions built before early 2003. There is a new part that is a hardened 4th clutch hub shaft. Either that or the 2 clutches that are in the trans for 4th gear (yeah, only 2 frictions) are shot. More likely they are thin and the 4th hub shaft is nearly stripped.

On the rest, most of the shifting by the trans is controlled by the pcm based on inputs from the maf, tps and map sensors. If any are not functioning properly you may get horrible shifting etc. Beyond that there is a common pressure control soleniod, and various valve body or leaking channel plate gasket that may cause the issues.

Since most of this points to a rebuild or a lot of work inside the trans, I'd suggest sourcing a replacement. The trans is very common and typically not overly expensive. Since you replaced the soleniods, a trans swap is well within your abilities.

[dsmuts]

Having to shift manually

[BillBoost37]

I think that would point more to the valve body.


Talking aloud here.....
When you put the car in D, 3, 2, or 1 the foward band is engaged by the servo. When you drop the car into 2 or 1 the manual 2-1 band is also engaged along with the forward band.

The gear selection for 1 or 2 still allows the trans to shift into 2nd when it reaches certain parameters, it will hold 1st longer though. This IIRC is based on pcm programming and not the valve body.

Choosing 3rd on the gear selector keeps fluid from reaching the 4th feed for it's clutch piston.