Several months ago I lost third gear in my 92 firebird (3.1L v6 w/ auto trans). Dad and I started to remove it but he decided it was too dangerous for us to do it alone in his driveway and paid to have it taken to a shop and rebuilt. Fast forward a few months and I go pick my baby up...except there is a noticeable lack of power once she shifts into 2nd and 3rd. After sorting out an issue with the car shutting off and refusing to start again the issue still remains. under light acceleration she shifts into 2nd at ~3.5k rpm give or take. under heavy acceleration she shifts at ~4k rpm. in the light accel case she promptly shifts from 2nd to 3rd almost instantly keeping the rpms at 2.5k. under heavy she shifts into 2nd then instantly into 3rd. I am going to disconnect the battery and reset the ecm to see if it basically needs to relearn from when i was driving prior to the rebuild. According to my dad, the tech, who claims to have rebuilt 5 firebirds, removed several check ***** from the transmission because it "increases longevity of the transmission". I can not find anything related to such a "modification" from either aftermarket, personal, or dealer sources.....and as a physicist the lack of data is infuriating. Has anyone heard of doing this before or have any links to sources the explains the process reasoning and possibly data to show how it impacts the transmission?

Looking more into it the only thing I could find is that the 4 silver check ***** need to be reinstalled or replaced while the copper colored check ball of larger diameter can be left out. The copper ball maintains pressure in the transmission to allow some drivability should the TV cable break.

 

Depending on Ones level of comprehension, relative to the physics of the Hydraulic Circuits involved (Yours may be rather high relative to the average member here)...
A worth while discussion here will most likely get rather lengthy.

In addition, many of these "modifications" are widely disagreed upon..
except among some of the select few designers of the modifications that are performing at the highest levels relative to the THM700-R4 Transmission.

So... where do you wish to start?

 

Astrophysics is more my area than hydrodynamics. However, I couldnt seem to find anything about modifications of this nature. I plan on calling the shop who worked on it tomorrow since i still have warranty from their repair. I just wanted to do some research and collect some data before just running back to them and seeming like im accusing them of making a mistake.

 

Alright, however before diving into the Transmission...
Generally if the Shift occurs, holds (RPM does not zing to Engine RPM Red-Line), but the Vehicle will NOT accel (RPM will not climb/ climbs slowly)...
The Engine is usually the issue.

If the Engine RPM does climb or zing on wards, where the Vehicle does NOT accelerate...
Then the Transmission or Torque Converter is Slipping.

Best way to initially confirm an issue here is to purchase, install, and use a 0 - 300 Psi Line Pressure Gauge to the Test-Port on the Driver's side of the Transmission Case.
Low Line Pressure during the symptoms you are experiencing/ Low Line Pressure overall, would be the sign to make the initial confirmation.