So I recently bought my brothers 91 Firebird off him that has a whole long list of work done to it. It has a 87 Grand National motor in it and he had it sitting for awhile before he moved to Chicago. Needless to say I couldn't let that care go out of the family so I bought it off him.

Had all the fluids changed out and got it all ready to ride for the summer. Starts fine and runs great UNTIL the motor warms up, after driving for about 10 - 15 mins. it randomly will have very rough shifts between 2nd and 3rd. Only does this when it is warm though.

Any thoughts on what it could be? A local car buddy told me it might just be some dirt/grit in the tranny from sitting for years outside. He recommended dropping the pan, cleaning it all out really good and then put fresh stuff in and see what happens.

Do any of you guys have any thoughts?

Thanks,
Matt

 

If it truly does have a Buick 3.8L in it then I doubt it's a TH700-R4 unless an adapter plate was used. It's most likely a TH200-4R in it.

 

Depends upon what you mean by a rough shift, but the shift timing on the 2-3 shift is critical. When it isn't correct the trans will either bind as it is in 2nd and 3rd at the same time. Or there will be a flare as the trans exits 2nd gear with a delay before 3rd is engaged.

Note that this is true for both the 700R4 and the 2004R.

RBob.

 

it is a true 3.8L Buick in it and yes there is a TCI adaptor to make the 700r4 work. Ran fine for my brother for years like it and then it sat for a few years.

It is like a thud thud thud then its in 3rd and it doesn't happen every time and its only when the car is fully warmed up.

 

maybe the torque converter is locking immediately when shifting to 3rd.