Hello!
I have some questions about my
Pontiac Trans Sport SE 3,1 1990.

1# When I been driving for about 20 miles the
gearbox locks itself in the third gear & it wont
shift down. I have to shift down to second
gear manual. But when I drive shorter distance
like 5-10 miles it works perfektly. What can it be?

2# How mutch ATF oil shall I put in
the transmission when I change the
oil & filter?

Best Regards
Kenny, Sweden

2# How much ATF oil shall I put in
the transmission when I change the
oil & filter?
Drain and refill (just dropping the oil pan): 4 qts.
Full overhaul (dry transmission and torque converter): 7qts

1# ... when I drive shorter distance ke 5-10 miles it works perfektly.
Temperature dependant, then...THe manual does not describe that condition.......it can be any sticky component, O-ring, seal, debris..hard to pinpoint. When you drop the oil pan, pay attention to presence of debris...maybe fresh new oil could modify the sensitivity to heat...otherwise, hope it goes away, or endure..or control valve surgery...keep us informed of development

Hi!
Thanks for the fast answer :)
You have to excuse my bad english.

I'm going to test to change oil & filter and put some Wynns AutomaticTransmission Treatment in it and se how it runns I'm
also going to put in a seperate oil cooler.

I just read in the autorepair forum that it also could be the TCC solenoid
(Torque Converter Clutch Solenoid).

But first I'm going to test changing the oil & mount the seperate oil cooler
this weekend.

I just read in the autorepair forum that it also could be the TCC solenoid.
Yes this is a known occurrence...but the symptoms would be different than those you described. It generally causes the engine to stall when coming to a stop......So..if you change your description, check this out:
http://www.automotiveforums.com/vbulletin/showthread.php?t=551757

Would this unit have the transmission lockup solenoid like my 89 Celebrity? Common problem I'm told. I'm told you can defeat it by disconnecting the wiring which will lower your gas mileage somewhat or go a step further and install an underdash switch in the circuit which you operate when coming to a stop. It was easy and best enough to change the lockup solenoid though and not really expensive either. On the Celebrity access through the left wheel well. I had to take the motor mount off.

I tried to disconnect the TCC solenoid & now it works. I'm going to order a new next week and change it.

Thanks for the quick answers =)