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2017 Sierra 1500 8-Speed Transmission Jerking/Hard Shifts - Anyone Else?

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Mark S. · rep 0 · May 25, 2:42 AM · 1 replies · solved · Question

Vehicle: 2017 GMC Sierra 1500 SLT

Hey everyone,

I've got a 2017 GMC Sierra 1500 SLT with the 5.3L V8 and the 8-speed automatic transmission. Lately, I've noticed some really harsh shifts, especially when downshifting at lower speeds or accelerating from a stop. It feels like a significant jerk, almost like being rear-ended sometimes. It's not consistent, but it's happening more frequently.

I've heard about some issues with these 8-speed transmissions. Is this a common problem for this model year? I'm worried about long-term reliability and don't want to ignore it if it's a known defect. I'm wondering if there are any TSBs or recalls I should be aware of before taking it to the dealer.

Any advice or shared experiences would be greatly appreciated!

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 25, 2:42 AM

0

ClearTheCode admin answer:

It sounds like you're experiencing symptoms commonly associated with the 8L90/8L45 8-speed automatic transmission found in many 2015-2019 GM trucks and SUVs, including your 2017 GMC Sierra 1500. This is a widely reported issue.

Common Causes:

  1. Torque Converter Issues: A common culprit is a faulty torque converter, which can lead to shuddering, harsh shifts, and transmission fluid degradation.
  2. Transmission Fluid Degradation: The original transmission fluid (Dexron HP) used in these units was prone to breaking down prematurely, leading to clutch wear and shudder.
  3. Valve Body/Solenoid Problems: Less commonly, issues with the valve body or solenoids can cause erratic shifting.
  4. Software Calibration: Sometimes, updated transmission control module (TCM) software can help mitigate some of the shifting harshness, though it's often a temporary fix if mechanical issues persist.

When to See a Shop:

  • Immediately: If you notice any warning lights (e.g., Check Engine Light, Service Transmission), or if the jerking becomes severe, making the vehicle unsafe to drive.
  • Soon: If the symptoms are consistent and worsening. Continued driving with a failing torque converter can cause further damage to the transmission.

Diagnostics & Potential Solutions:

  1. Check for TSBs: There are several Technical Service Bulletins (TSBs) related to these transmissions, specifically TSB 18-NA-355 (superseding earlier ones) which addresses shudder and recommends a transmission fluid flush and refill with a specific Mobil 1 Synthetic LV ATF HP fluid. This fluid is designed to be more resistant to shear and wear.
  2. Diagnostic Scan: A professional shop will scan for diagnostic trouble codes (DTCs). Common codes related to transmission issues include P0700 (Transmission Control System Malfunction) and P0796 (Pressure Control Solenoid 'C' Performance or Stuck Off).
  3. Test Drive & Inspection: A technician will perform a detailed test drive to confirm symptoms and visually inspect for leaks or external damage.
  4. Fluid Flush & Filter Replacement: If the TSB applies, a double flush with the specified fluid is often the first step.
  5. Torque Converter Replacement: If the fluid flush doesn't resolve the issue, or if the shudder is severe, torque converter replacement is often necessary. In some cases, the entire transmission might need to be rebuilt or replaced, though this is less common for just shuddering.

Given the widespread nature of this issue, it's advisable to have it checked by a GMC dealership or a reputable transmission specialist who is familiar with these specific 8-speed units. Be prepared to discuss the TSBs with them.

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