200R4 shifts early?

[LukeZ]

i have a serious question about my transmission that has been bothering me since I got my car almost a year ago (October 16th, I think it was).

I have a 305, a 200R4 overdrive transmission, and 2.56:1 rear end gears. I don't have a tach, so I can't tell you what rpms my car shifts at, but here is the problem: at around 35 or 40mph, my car shifts into 3rd. Feels fine and dandy. Then, literally like 1 second later, my cars rpms just drop, and the engine sounds really deep and slow (I guess an easy way to explain this would be to say that it goes from vrooooom to wom-wom-wom-wom-wom ). This is when I have the gear selector on Overdrive, which is (D). This doesn't happen in Drive, which is D. I assume that my car is just shifting into 4th at a really low speed. Does anyone know why, and if a transmission shop could change this? Does anyone else have this problem? I was looking at getting 3.42s, so I didn't know if this would be a problem.

 

[Bill C.]

I had a similar problem with a mustang ended up being the throttle position sensor. It would bog down then it wouldn't down shift back to 3rd even if you put peddle to the floor. Other thing could be the speed sensor.

 

[TexasT]

It is shifting into od(4th) then shortly thereafter probably locking the converter clutch. Just drive it in d around town, then if you get on the highway you can shift it to OD.

 

[Longroof79]

Having overdrive and a high gear (low numerically) I could see where it would tend to lug. I agree with Rich, shifting to D around town is a good alternative. I'm sure it shifts in and out of lockup frequently. The engine will run happier with a lower gear..3.23, 3.42, 3.73.

 

[81_El_Homewrecker]

As Rich said, I had a problem with my lock up in a 350 where the second it shifted into third it would lock up and lug like yours. Try unplugging the lock up connector on the trans and see if your problem goes away. Also, it shouldn't be locking in third. Are you maybe confusing third with OD?