The Hydra-Matic 8L90 (heavy-duty trucks, SUVs, and performance cars) and 8L45 (lighter sedans and, more recently, midsize trucks) are GM's in-house 8-speed automatics, introduced for the 2015 model year to replace the outgoing 6-speeds. Both use planetary gearsets arranged so that two gearsets share power flow in parallel rather than strictly in series — a layout related to the patented architecture used industry-wide in ZF's 8HP, with GM's own arrangement swapping the position of two of the four gearsets. The payoff is eight forward ratios built from fewer clutch packs than a conventional design, with shift times GM has quoted at roughly 0.2 seconds.

Two specific, well-documented failure modes drive almost all of the shudder and harsh-shift complaints:

Defective ATF and torque-converter-clutch (TCC) shudder. To hit fuel-economy targets, the 8L90/8L45 runs its torque converter clutch in continuous, controlled slip across a wide speed band rather than locking it fully — the clutch plates ride on a thin, precisely engineered film of automatic transmission fluid almost all the time the vehicle is moving. That design only works if the fluid's friction modifiers hold a stable, rising friction curve as slip speed changes. GM's original factory fill did not reliably do that: it absorbed moisture through the transmission's vent system and its friction curve degraded with age, causing the clutch to alternate between gripping and releasing — "stick-slip" — instead of slipping smoothly. GM's own service bulletin describes the result as "a shake and/or shudder during light throttle acceleration," most noticeable between roughly 48–104 km/h (30–65 mph), that can feel like driving over rumble strips or rough pavement, and can appear during acceleration, coast-down, or shift maneuvers.

Valve body air-purge failure. The valve body is the transmission's hydraulic control center — a cast housing full of narrow channels and spring-loaded spool valves that route pressurized fluid to the correct clutch pack for each of the eight gears. A properly purged valve body clears trapped air from those channels quickly so pressure builds predictably. Owners and independent transmission technicians allege the 8L90/8L45 valve body architecture — including a converter-feed-limit valve prone to bore wear — does not purge trapped air adequately, especially after the vehicle has sat overnight. The result is the harsh, delayed "first shift of the day": a hard clunk or hesitation into gear that eases once the fluid warms and pressure stabilizes.

GM revised its factory fluid specification in December 2018 and introduced an improved formulation — referred to in litigation filings as "Mod1a" — in March 2019, and later redesigned the hardware itself: a second-generation unit (the 8L80) arrived in the 2024 Chevrolet Silverado 1500 and GMC Sierra 1500 with new mechanical components, not just a fluid change. Neither fix can be retrofitted into the internal architecture of transmissions already built to the earlier design; owners of those vehicles are limited to fluid changes, valve-body rework, or component replacement.

The 8L90 and 8L45 were used across most of GM's rear-wheel-drive-based lineup. Exact application depends on engine and trim (diesel and some Allison-equipped heavy-duty trucks are not affected), so a repair order or RPO code decode is the most reliable way to confirm a specific VIN — but within the 2019–2026 window, the transmissions appear in:

Owners of any of the above should pull their build sheet or RPO codes (M5U, MHT, MQB, MQC, MYC, MYD, MGM, MGU, MHK) to confirm which unit their specific vehicle carries before pursuing a claim.

The complaint pattern is remarkably consistent across brands and body styles: a rumble or vibration under light throttle at steady highway speed, a delayed or clunky first shift in the morning, occasional flare-ups or hesitation on takeoff, and — in a smaller but recurring set of posts — a report that the truck or SUV briefly failed to respond to the accelerator. Owners describe the sensation most often as "driving over rumble strips," a phrase that also appears in GM's own bulletins.

Discussion is concentrated less on general social platforms and more in brand-specific owner communities, where thousands of pages of troubleshooting threads have accumulated since 2015:

Reddit hosts the same complaint pattern in scattered form across general-interest communities for these trucks and SUVs, but — unlike the dedicated brand forums above — has no single, long-running thread that concentrates the discussion; owners are more likely to find (and get) a useful answer on SilveradoSierra.com, GM-Trucks.com, or the Cadillac Owners Forum.

GM has never issued a formal NHTSA safety recall (a Part 573 recall) specifically for 8L90/8L45 shudder or valve-body air purge. Instead, the company has addressed the condition through a long series of technical service bulletins (TSBs) — internal repair guidance filed with, and archived by, NHTSA, but not a recall — supplemented by owner complaints filed directly with the agency's Office of Defects Investigation. Litigation filings put the TSB count addressing shift-quality and shudder symptoms since 2015 in the low teens; some technical and trade-press sources cite a much larger number of bulletins and service updates touching related shift-feel complaints across the broader 8-speed family. Key bulletins include:

Because no recall exists for the transmission condition itself, a repair-order paper trail and a formal warranty or lemon law claim — not a recall remedy — are the main paths to relief for the shudder and valve-body complaints.

No settlement or final judgment has been reported in either case as of this writing. Owners can track developments through the case-tracking pages below rather than rely on a single news article, since the docket has moved several times in the past two years:

• ClassAction.org — GM 8-Speed Transmission Defect Lawsuits
• Cohen Milstein — General Motors Litigation case study
• Berger Montague — Speerly v. General Motors, LLC
• CourtListener — Speerly v. GM, 6th Cir. en banc opinion
• Top Class Actions — case status updates

Independent of the class action's fate, an individual owner in New York or New Jersey generally has several claims available. Each turns on a documented repair history, so every dealer visit — with mileage, date, and the technician's own narrative — is evidence.

The affected transmission sits behind a wide range of body styles — full-size pickups, full-size SUVs, midsize trucks, and rear-drive sedans and coupes — all sharing the same internal unit and the same complaint pattern:

Note on imagery: this report uses original diagrams rather than manufacturer photographs to avoid any copyright or trademark issue on a published legal-marketing page. Before publishing, swap in licensed stock photography or your own photographed intake vehicles/parts if you want real photos alongside these diagrams.

Common short-tail terms:

Long-tail phrases (higher intent, lower competition):