With the springs in first (inverted) and the piston on top this created an opposite effect, more spring tension created a softer shift.
When the Piston was installed into the housing first this setup created the band apply pressure against the spring tension, the heavier the spring tension the firmer the shift. In the later years it was fitted with the springs in the housing first and the piston on top of the spring. In the early days, the piston was installed into the housing first with the spring on top. The 1-2 Accumulator piston and spring came in many different configurations. NOTE: The 554 is intended for the 4 cylinder and the 2.8 V6 only. With the exception of the 093 piston that is primarily used in Corvettes and HP Camaros most everything else that you are working on should have the 553 or 159 piston in it. Having the wrong apply area for the application can cause either a soft or slide bang 1-2 shift or a harsh 1-2 shift. There are four different OE servo sizes that are used with this transmission. The valve needs to be carefully inspected to make sure it is not sticking and that the spring is not cocked in the bore. The accumulator system is one of the systems used for controlling and influencing the 1-2 and 3-4 shift.
This occurs when the ECM EPC solenoid driver has failed especially on the 1993-1997 models. Far too often the PID will display the proper commanded amperage when in fact it is wrong. It is not advisable to rely on the EPC solenoid commanded amperage PID on the scan tool. Diagnosing line pressure problems on a 4L60E requires a pressure gauge and DVOM to measure the commanded EPC solenoid amperage. Once the TCC slippage problems have been addressed the other line pressure areas of concern are the ECM EPC solenoid driver failure, lean misfire conditions, MAF sensor problems and the EPC solenoid itself. Many of the harsh 1-2 problems are due to the TCC slippage complaints setting P1870-P0894 codes and putting the transmission into high line pressure mode. Line pressure boost control has been the Achilles heel of the 4L60E for a long time. Let us have a look at the systems and potential problems in a 4L60E that can cause a harsh 1-2 shift. It amazes me when a transmission that has been around for this long can throw a new twist on a common problem and blindside you. The 4L60E transmission platform has been in service from 1993-2015, that’s 22 years.