Owner's Problem Description
The owner reports that after getting the 1985 Chevy Blazer running again, it has gone through two flexplates, both exhibiting fractures radiating from the bolt holes outward. The transmission has been rebuilt and the starter replaced recently. The owner is concerned whether the starter is causing these flexplate failures, as the issue is unusual and has stumped previous mechanics.
Professional Technical Analysis
This case involves a 1985 Chevy Blazer experiencing repeated failures of the flexplate, with two replacements fracturing near the bolt holes. This vehicle is powered by a 5.0L V8 engine, and with an estimated mileage of around 150,000 miles, the owner has recently rebuilt the transmission and replaced the starter. The flexplate failures are characterized by cracks emanating from the bolt holes, and one flexplate has completely separated from the main body. The owner has confirmed that the flexplate fits snugly on the crankshaft and that new bolts were used during installation. The critical first step in diagnosing this problem is to assess the torque converter's installation; if the converter is not seated properly, it could cause flexplate bowing when tightened, leading to stress fractures. Additionally, it is essential to inspect the starter's engagement depth and the condition of the bendix drive to ensure it does not inadvertently cause excessive force on the flexplate during cranking. It is uncommon to see flexplate failures like this, suggesting a potential installation issue or a misalignment in the drivetrain components. A thorough examination of the transmission mount alignment and the overall drivetrain geometry is necessary to rule out any abnormalities that could stress the flexplate.
Possible Causes
Most common causes (ordered by frequency):
- Improper Torque Converter Installation: If the torque converter is not fully seated in the crankshaft, it can lead to misalignment that causes the flexplate to bow when the bolts are tightened. This misalignment places undue stress on the flexplate, resulting in cracks near the bolt holes. Ensure that the torque converter is fully seated and the flexplate is installed correctly without any bowing. - Visual inspection shows cracks radiating from bolt holes, indicating misalignment. Flexplate should remain flat when installed correctly.
- Starter Engagement Issues: If the starter's bendix is engaging too deeply or is misaligned, it could apply excessive force to the flexplate during cranking. This excessive force can lead to fractures in the flexplate material, especially if the starter is not functioning properly. Verify the starter's installation and ensure it engages correctly without excessive force. - Starter shows signs of wear, possible misalignment indicated by uneven engagement with the flexplate. Measure bendix engagement depth.
- Drivetrain Misalignment: Any misalignment within the drivetrain components, including the transmission and engine mounts, could result in flexplate stress. Inspect the alignment of the engine and transmission mounts to ensure they are positioned correctly and securely. - Visual inspection of mounts shows signs of wear or displacement, indicating potential alignment issues.
Diagnostic Steps
Professional Diagnosis Process
Follow these systematic steps to accurately diagnose the issue. Each step builds on the previous one to ensure accurate diagnosis.
- STEP 1 - Visual Inspection: Begin with a thorough visual inspection of the flexplate, starter, and torque converter. Check for signs of misalignment, such as unusual wear patterns or bowing of the flexplate. Ensure that all mounting points are secure and that there are no visible cracks on the flexplate beyond the existing fractures.
- STEP 2 - Torque Converter Verification: Remove the transmission inspection cover to check the engagement of the torque converter with the flexplate. Confirm that the converter is fully seated against the crankshaft. Reinstall and torque the flexplate bolts to specification, typically 30 lb-ft, ensuring no bowing occurs.
- STEP 3 - Starter Function Check: Test the starter's engagement to ensure it is functioning properly. Measure the bendix engagement depth and check for any signs of wear or damage. Compare readings with manufacturer specifications to confirm proper operation.
- STEP 4 - Drivetrain Alignment Assessment: Perform an alignment check on the drivetrain components. Inspect engine and transmission mounts for wear or misalignment. Ensure that all components are securely mounted and aligned to prevent undue stress on the flexplate.
