Common problems with the 4L60E transmission include the third and fourth gears not working, slow or slipping reverse gear and sudden grinding noise in second gear. Almost every rear-wheel drive vehicle manufactured by General Motors features the 4L60E transmission.
If the third and fourth gears are not available, the third and fourth clutches are worn out. Remove and rebuild the transmission to fix the issue. The car is still safe to drive in second gear.
Fluid leaks, worn-out clutches and broken sunshells may cause slow or slipping reverse gear. Removing the checkball from its cage in the rear of the transmission and adding an additive with high viscosity may fix the problem.
If the car makes a grinding noise in second gear, the sunshell is broken. Remove and rebuild the transmission to fix the problem, and do not drive the car until the sunshell is fixed to avoid further damage.