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2018 Silverado 8-Speed Transmission Shudder/Hard Shifts

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Mike T. · rep 0 · May 25, 1:44 AM · 1 replies · solved · Question

Vehicle: 2018 Chevrolet Silverado 1500 LT

My 2018 Chevrolet Silverado 1500 LT, with the 5.3L V8 and the 8-speed automatic transmission, has been acting up lately. When I'm driving at lower speeds or just starting from a stop, it feels like the transmission shudders or hesitates, almost like it's struggling to find the right gear. Sometimes, the shifts feel really harsh, especially between 1st and 2nd, or 2nd and 3rd. It's got about 75,000 miles on it.

I've read online that this might be a common issue with these 8-speed transmissions. Is there a known fix or a TSB for this? I'm worried about the long-term reliability and don't want to ignore it if it's a sign of a bigger problem. Any advice on what I should check or ask my mechanic to look for?

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 25, 1:44 AM

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ClearTheCode admin answer: The issues you're describing with your 2018 Chevrolet Silverado's 8-speed automatic transmission (8L90 or 8L45) are indeed quite common and have been widely reported by owners. This often manifests as a shudder, harsh shifts, or hesitation, particularly at low speeds or during light acceleration.

  1. Causes and TSBs:

    • Torque Converter Clutch (TCC) Shudder: A primary culprit is often the torque converter clutch, which can cause a shudder due to fluid breakdown or design characteristics.
    • Transmission Fluid Degradation: The original DEXRON HP transmission fluid used in these units was found to be prone to breaking down prematurely, leading to friction material wear and shuddering.
    • TSB #18-NA-355: GM issued Technical Service Bulletin (TSB) #18-NA-355 (superseding earlier TSBs like 16-NA-175) specifically addressing "Shudder During Light Throttle Acceleration" on many 8-speed automatic transmissions. This TSB often recommends a triple flush procedure using a new, improved Mobil 1 Synthetic LV ATF HP fluid (part number 19417577). This new fluid has different friction modifiers designed to prevent the shudder.
    • Valve Body Issues: Less commonly, issues with the valve body or solenoids can contribute to harsh shifting.

  2. Diagnostic Steps:

    • A qualified technician will typically connect a diagnostic scanner to check for any stored diagnostic trouble codes (DTCs), though TCC shudder may not always trigger a code initially.
    • They will perform a road test to replicate the condition and observe transmission performance data.
    • Inspection of the transmission fluid condition (color, smell) can also provide clues.

  3. When to See a Shop:

    • You should schedule an appointment with a Chevrolet dealership or a reputable independent transmission specialist as soon as possible.
    • Specifically mention TSB #18-NA-355 and inquire about the transmission fluid flush procedure. Many owners have reported significant improvement or complete resolution after this service.
    • If the shudder persists after the fluid flush, further diagnosis may be required, potentially including torque converter replacement or inspection of internal transmission components. Ignoring these symptoms can lead to accelerated wear and more costly repairs down the line.

It's important to address this proactively to maintain the reliability and longevity of your vehicle's transmission.

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