It's the reverse reaction sun shell, it's stripped. Very common problem.(I assume you have a 4l60e trans). This bulletin might help. Some customers may comment on a no reverse, no second or no fourth gear condition. First and third gears will operate properly.
The reaction sun gear (673) may not hold inside the reaction sun shell (670). Follow the service procedure below for diagnosis and correction of the no reverse, no second, no forth condition.
Important: If metallic debris is found on the transmission magnet, the transmission must be completely disassembled and cleaned. Metallic debris is defined as broken parts and pieces of internal transmission components. This should not be confused with typical "normal" fine particles found on all transmission magnets. Failure to properly clean the transmission case and internal components may lead to additional repeat repairs.
Remove the transmission oil pan and inspect the magnet in the bottom of the pan for metal debris. Refer to SI Document ID #825141.
Remove the transmission from the vehicle. Refer to the appropriate SI document.
" Inspect all the transmission components for damage or wear. Replace all damaged or worn components. The parts list below should be sufficient to correct this concern.
" This condition does not normally require replacement of the transmission completely. Components such as clutches, valve body, pump and torque converters will NOT require replacement to correct this condition.
Disassemble the transmission and replace the appropriate parts listed below. Reaction carrier shaft
(669) reaction shaft thrust washer / bearing
(670) reaction sun shell
(674) reaction shell thrust washer
Reinstall the transmission in the vehicle. This might help
Thursday, July 24th, 2008 AT 8:17 PM