It is common to have poor 3-4 shifts, no 4th Gear or a burned 4th clutch in GM 4T65-E units. This can be caused by excess wear at the 3-4 accumulator piston pin bore, which allows 4th clutch oil to exhaust and can result in harsh 4th, no 4th Gear or a burned 4th clutch. Pin bore wear also reduces 3rd clutch pressure during 3-4 shift. The 4th shift quality depends on the condition of the piston and accumulator valves. If the 4th accumulator piston seizes, the 4th shift will be very hard. Sonnax 3-4 accumulator piston 84880M-01 restores accumulator pressure and eliminates cross leaks.

• Piston is manufactured from high-grade billet aluminum to prevent wear
• Tight tolerances and surface finish restore proper clearances
• Piston accepts OE or standard replacement D-ring