Finally tore down my 4L60E and discovered the 3rd clutch apply piston is cracked. I heard that TCI used to sell billet upgrades, but I can't seem to find anyone that sells them. Anyone know a place that has em or can suggest another upgrade?

 

Are you talking about the 3-4 piston in the bottom of the input drum? This can be aluminum, but the later units used a molded rubber piston, which is interchangable. I have seen only one of these crack in the last 12 years, so it is not a common occurrence. The one that is known for cracking in the 4L60E's is the aluminum forward piston, but the later units used a molded rubber piston, which is interchangable here also.

 

sorry I don't know much about the 4L60E. From what I gather, yes it also called the forward clutch apply piston. my trans is from a 95 and the piece is aluminum. The crack starts from the backside edge and goes completely across the face. The last owner abused the car a lot, so I'm not too surprised.

 

This is the forward piston. Use a molded rubber forward piston, along with the molded rubber overrun piston. You will need to use the overrun/forward spring reatiner from a later unit, as it comes with a retainer on the bottom, which is needed when going to a molded rubber setup. This bottom retainer was not necessary when using the aluminum overrun piston.