8L90 Transmission Problems & Cures

The GM 8L90 is an eight-speed rear-wheel-drive automatic. GM introduced it in 2014 for the 2015 model year in the Corvette, full-size pickups and SUVs. Its smaller sister is the 8L45. This page covers the problems GM and the valve-body specialists have documented, what fixes them, and the 8L90 parts we stock.

8L90 at a glance

Applications listed in GM bulletin 18-NA-355

The bulletin list is not every 8L90 vehicle; check your RPO code (M5U or M5X).

Problem 1: shudder at light throttle

The best-known 8L90 complaint is a shake or shudder at 25–80 mph on light throttle, felt as the torque converter clutch applies. GM addressed it in service bulletins 16-NA-175 and 18-NA-355. The current GM fix is a fluid exchange with the updated blue-label Mobil 1 Synthetic LV ATF HP, done with GM’s exchange equipment (triple drain and fill on the Corvette and CT6). GM’s TechLink explains that the original fluid tends to absorb moisture. GM also warns that mixing in other fluids or additives will not give satisfactory results.

• Superior Shudder~Solution valve body upgrade kit (STP-STL8L90): Superior’s kit for TCC shudder and chatter; in most cases it installs from the pan without removing the transmission.
• Sonnax TCC Zip Kit (8L45-8L90-TCC-ZIP): seals worn lube, converter limit, line pressure and converter apply circuits.
• TransGo SHIFT KIT valve body repair kit (SK8L90): TransGo lists TCC instability, overheated converters and codes P0218 and P0741. Requires TransGo tooling.
• TCC lock-up solenoid (24272280)

Problem 2: harsh, flared or slipping shifts and burnt clutches

GM released software updates (bulletin 16-NA-412) for harsh shifts, but on higher-mileage units Sonnax and TransGo point to valve-body wear. The signal accumulator piston bores and the clutch control valve bores wear and leak pressure, so the clutches apply with less force: flares, harsh or erratic shifts, slipping and burnt clutches follow. Worn pressure regulator and shuttle valves cause high or low line pressure. Sonnax warns that very high line pressure can crack the valve body.

• Sonnax Shift Zip Kit (8L45-8L90-SHIFT-ZIP)
• Sonnax signal accumulator piston kit (154740-06K) · TransGo oversized pulse dampener pistons (8L90-PDP-OS)
• Sonnax S1 / S5 clutch control valve kit (154740-13K)
• Sonnax S2 / S3 / S4 / TCC clutch control valve kit (154740-11K)
• TransGo drop-in PR shuttle valve assembly (8L90-SHUTTLE-OES)
• LPC pressure control solenoid (24272282)

Keeping it cool

From the factory, a thermostatic valve limits cooler flow until the fluid warms up. Two kits give full-time cooler flow: Superior Sure-Cool cooler flow system (STP-STL010) and TransGo cooler flow bypass delete kit (6L80-CLR-BYPASS).

Rebuilding an 8L90

• Overhaul kit (KP33900H) · build your own 8L90 rebuild kit (RK8L90)
• Raybestos HT friction module (RHT96-322-Kit) · Raybestos GPZ heavy-duty friction module (RGPZ-019-Kit) · BorgWarner friction module (154Fric-BW-Kit)
• Steel plate module (224753A-Kit) · bushing kit (224625B)
• Oil filter (201710)
• Internal wire harness with temperature sensor, 8L90 2015–19 (D154446F)

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