Why does tranny shift into O/D before end of track?

[Rio97GT]

I have a headswapped 97 GT with the 4R70W and I cant keep it from shifting into overdrive at the track. After the 4.10's were installed, it would shift into O/D around 80 MPH no matter if I had it turned off or not. At the track it felt like I was letting off of the gas around the 1000' ft mark. The car ran a 14.0@93 MPH...it ran a 14.6@92 when it was stock) I have a diablochip (which was supposed to fix all this shift point stuff), but the tuner said that there wasnt anything he could do to make it not do this. What do you guys think about this?

Thanks,
Michael

 

[tjm73]

Sounds like your tuner is feeding you a line of crap to me. I with a comuter tune you have just as much control over the tranny as the engine.

 

[Rio97GT]

Has anyone else had shifting problems with 4.10's in an auto?

 

[007]

The tuner has somehow fixed your speedo and not your shifts. I didnt even think you could do that. What if you have the O/D button engaged to stop the shift?

I have 4.10s in my auto and it hits overdrive somewhere around 110mph. If your 3-4 shift is screwed your other shifts probably are too. I think the tuner has no idea what hes doing. There arent many who can do a decent job on autos.

The early shifting is no doubt the reason for your low trap speed. Get it fixed and youll trap 100+ with a better ET. You dont want to be in OD at the track, its way too wide a gear.

 

[NiteRydaGT]

My 4R70W does the same thing at 80. I haven't noticed that it made a difference I just noticed the o/d light goes off.

 

[Rio97GT]

The tuner has somehow fixed your speedo and not your shifts. I didnt even think you could do that. What if you have the O/D button engaged to stop the shift?

I have 4.10s in my auto and it hits overdrive somewhere around 110mph. If your 3-4 shift is screwed your other shifts probably are too. I think the tuner has no idea what hes doing. There arent many who can do a decent job on autos.

The early shifting is no doubt the reason for your low trap speed. Get it fixed and youll trap 100+ with a better ET. You dont want to be in OD at the track, its way too wide a gear.

If I could trap over 100mph, that would be a world of difference over it falling on it's face in O/D.

My 4R70W does the same thing at 80. I haven't noticed that it made a difference I just noticed the o/d light goes off.

This seems to be a problem with the 96-98 cars and not the 99+'s for some reason. Are there any 96-98 guys who have gotten around this and how? Right now it seems that the only way to fix it is to put in a 5-speed.

BTW, how are those VT n/a cams? I'd like to get those, but I'm not too sure how big of a difference they would make.

 

[NiteRydaGT]

BTW, how are those VT n/a cams? I'd like to get those, but I'm not too sure how big of a difference they would make.

I can't say what difference the cams made because I did the headswap and cams at the same time. I'm still in the break-in period so I haven't been able to smash the pedal but she really starts to pull over 3k. My tuner estimated 250-260 rwhp. VT claims something like 22RWHP at peak with the stage 1's I believe.

 

[Rio97GT]

Sounds good. Let us know how it feels when you really get on it, and what it runs at the track.

 

[98GTfromGA]

Guys,
I had the same problem when my car was an automatic. I have 3.73 and it would do the same thing at about 80 mph. I got a diablo chip and it fixed it.
Basically he told the computer to not to shift into overdrive until 129 mph.
Now I have a 5 speed. It is frustrating having that problem.