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2018 Sierra 1500 8-Speed Transmission Shudder - Anyone Else?

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Mike T. · rep 0 · May 24, 1:29 PM · 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, and I've been noticing a really annoying shudder lately. It feels like driving over rumble strips, especially when I'm lightly accelerating between 30-50 mph, or sometimes right after a shift.

It's not constant, but it's definitely getting more frequent. It almost feels like the transmission is struggling to decide which gear to be in, or maybe there's some kind of torque converter issue. I've heard some talk about these 8-speeds having problems.

Has anyone else experienced this with their 2016-2020 Sierra or other GMC trucks with this transmission? What did your dealer say or what was the fix? I'm trying to gather some info before I take it in. Thanks for any help!

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 24, 1:29 PM

0

ClearTheCode admin answer:

The transmission shudder you're describing in your 2018 GMC Sierra 1500 with the 8-speed automatic is a well-documented concern for many owners of GM vehicles equipped with this transmission (8L90/8L45). It's often referred to as 'torque converter shudder' or 'transmission shudder'.

Here's what you should know and what steps to take:

  1. Common Causes:

    • Degraded Transmission Fluid: Over time, the original DEXRON HP transmission fluid could degrade, leading to friction material breakdown and microscopic air bubbles (aeration). This can cause inconsistent clutch engagement and the shudder you feel.
    • Torque Converter Issues: The torque converter itself might be experiencing internal wear or issues with its clutch, leading to inconsistent lock-up.
    • Software Calibration: In some cases, the transmission control module (TCM) software calibration might contribute to the issue, though this is less common for severe shudder.

  2. Diagnostic Steps:

    • Fluid Inspection: A qualified technician will first check the transmission fluid level and condition. They'll look for signs of contamination or unusual color/smell.
    • Test Drive & Data Logging: Replicating the shudder during a test drive while monitoring transmission parameters with a diagnostic scanner can help pinpoint the exact conditions under which it occurs.
    • OBD Codes: While shudder often doesn't immediately throw a specific code, persistent issues or severe slip could eventually trigger a P0700 (Transmission Control System Malfunction) or other transmission-related codes.

  3. Potential Solutions:

    • Transmission Fluid Flush & Refill: GM released a Technical Service Bulletin (TSB #18-NA-355, later superseded by others) recommending a specific transmission fluid exchange procedure using a new, improved DEXRON ULV (Ultra Low Viscosity) fluid. This often involves multiple flushes to thoroughly replace the old fluid. This is frequently the first and most effective step.
    • Torque Converter Replacement: If the fluid exchange doesn't resolve the shudder, or if internal damage is suspected, the torque converter might need to be replaced.
    • Transmission Replacement/Rebuild: In severe or neglected cases, the entire transmission might require replacement or a rebuild, though this is less common for shudder alone without other major failure symptoms.

  4. When to See a Shop:

    • You should take your Sierra to a reputable GMC dealership or an independent transmission specialist as soon as possible. Continuing to drive with a significant transmission shudder can exacerbate wear and potentially lead to more costly repairs down the line.
    • Be sure to describe the exact conditions when the shudder occurs to help the technician diagnose it accurately. Mentioning the TSBs related to 8-speed transmission shudder might also be helpful.

Addressing this issue promptly can prevent further damage and restore smooth operation to your truck's drivetrain.

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