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2018 Sierra 1500 8-Speed Transmission Shudder - Is this normal?

0

Kim L. · rep 0 · May 22, 3:45 AM · 1 replies · solved · Question

Vehicle: 2018 GMC Sierra 1500 SLT

Hey everyone,

I've got a 2018 GMC Sierra 1500 SLT with the 5.3L V8 and the 8-speed automatic transmission, currently at about 65,000 miles. Lately, I've been experiencing a noticeable shudder or vibration, especially when accelerating gently between 40-60 mph, often when it's shifting between 4th and 5th gear, or 5th and 6th.

It feels like driving over rumble strips for a few seconds. It's not constant, but it's happening more frequently now. I've heard about issues with these transmissions, but I'm not sure if this is what people are talking about. Is this a known problem, and what should I be looking for?

Any advice or shared experiences would be greatly appreciated!

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 3:45 AM

0

ClearTheCode admin answer:

  1. Understand the Issue: The shudder you're describing in your 2018 GMC Sierra 1500's 8-speed transmission (GM 8L90/8L45) is a widely reported concern, often referred to as the 'GM 8-speed shudder.' It's typically caused by issues with the transmission fluid breaking down prematurely or a faulty torque converter.

  2. Common Causes:

    • Degraded Transmission Fluid: The original Dexron HP transmission fluid used in these units can degrade, leading to friction material breakdown and shudder. GM has since released a new fluid (Mobil 1 Synthetic LV ATF HP) to address this.
    • Torque Converter Clutch (TCC) Issues: A failing torque converter can also cause shudder, especially during lock-up, as it struggles to maintain a smooth connection between the engine and transmission.

  3. Diagnostic Steps & TSBs:

    • Check for TSBs: GM has issued Technical Service Bulletins (TSBs), specifically TSB 18-NA-355, which addresses this shudder. It often recommends a triple flush of the transmission fluid with the updated Mobil 1 fluid.
    • Fluid Inspection: A qualified technician can inspect your transmission fluid for signs of degradation or metallic particles.
    • Scan for Codes: While a shudder might not always trigger a Check Engine Light, a diagnostic scan can sometimes reveal pending or historical transmission-related codes (e.g., P0741 - Torque Converter Clutch Circuit Performance).

  4. When to See a Shop:

    • Immediately: If the shudder is severe, accompanied by warning lights, or if you notice any changes in shifting behavior (hard shifts, slipping).
    • Soon: Even if mild, it's best to have it inspected by a GMC dealer or a reputable transmission specialist. Addressing it early can prevent more extensive and costly damage to the transmission or torque converter.

Discuss the TSB with your service advisor and inquire about the updated fluid flush procedure.

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