Transmission trouble
Transmission model is a 4R70W,totally electronic,no vacuum to the trans.A common failure on that transmission is the 1-2 accumulator springs...they break,causing a harsh 1-2 upshift.An accumulator is a mechanical/hydraulic assembly also called an accumulator piston.It is made from steel with rubber lip seals bonded to the steel.The accumulator piston takes a certain portion of the hydraiulic fluid produced when the 1-2 upshift happens,and strokes up and down with springs providing resistance.It acts as a hydraulic shock absorber for the 1-2 upshift,providing cushion.When the springs break,it no longer provides shock absorption,hence the harsh upshift.It is located just inside the trans pan,on the passenger side front of the case.It is retained in the case with a cover and a round snap ring about 2" in diameter.A new piston and springs can be purchased from a transmission repair shop,or better yet,have them check the assembly for broken springs.Good luck
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