The flexplate connects the engine to the torque converter. It's a thin metal disc that flexes slightly under load. When it cracks or fails, you'll know it. Here's the complete guide to flexplates.
What the flexplate does
The flexplate:
- Connects crankshaft to torque converter
- Provides ring gear for starter
- Flexes slightly during operation (absorbs vibration)
- Mounts to the engine flange and converter
When the flexplate fails:
- Cracking sound from bellhousing area
- Vibration during acceleration
- Starter grinding (worn teeth)
- Engine misfires from improper rotation
- Eventually: complete failure, won't start
When to replace
Mandatory replacement:
- During engine swap
- During trans swap
- During converter replacement (sometimes)
- When cracked
- When ring gear teeth worn
Recommended replacement:
- Engine over 200K miles
- HD applications (towing, performance)
- After any significant impact (collision, ground strike)
- Race / drag applications (preventive)
Inspection during other work:
- During trans rebuild
- During converter replacement
- During engine work (front or rear seal, oil pan)
Common failures
1. Cracked flexplate
Cause: Vibration, age, heavy use, misalignment
Symptoms: Knocking/ticking sound from bellhousing, vibration
Severity: Must fix before catastrophic failure
2. Worn ring gear teeth
Cause: Starter engagement over time
Symptoms: Starter grinding, intermittent starts, partial engagement
Severity: Replace before starter damage
3. Loose flexplate
Cause: Bolts loosening, improper torque at install
Symptoms: Vibration, sometimes "clunk" on acceleration
Severity: Address immediately
4. Damaged bolt holes
Cause: Misalignment during install, excessive torque
Symptoms: Bolts loosen repeatedly, vibration
Severity: Replace flexplate
5. Bent flexplate (rare)
Cause: Impact (driveshaft hit), severe vibration
Symptoms: Severe vibration, possible starter issues
Severity: Replace immediately
Flexplate types by application
Stock automotive grade
Material: Stamped steel
Pros: Cheap, OE quality
Cons: Can crack under HD use
Cost: $40-100
HD aftermarket
Material: Higher-grade steel
Pros: Better fatigue resistance
Cons: Slightly more expensive
Cost: $60-150
SFI-certified racing flexplate
Material: Race-grade steel, additional reinforcement
Pros: Required for many race classes, ultimate strength
Cons: Expensive
Cost: $150-400
Billet flexplate
Material: CNC-machined from billet steel
Pros: Maximum strength, precision balance
Cons: Most expensive
Cost: $300-800
Specific applications
4L60E behind small block Chevy
- Standard 168-tooth flexplate
- Stock: $50-80
- HD aftermarket: $80-150
- SFI-rated race: $150-300
4L60E behind LS engine
- Specific LS flexplate (different from SBC)
- 168-tooth typical
- Stock: $60-100
- HD: $100-180
- Race: $200-400
4L80E behind big block
- HD flexplate required for HD applications
- Stock: $80-150
- HD: $150-300
- Race: $300-500
6L80 / 8L90 behind LS / LT
- Stock OEM: $80-150
- Aftermarket: $100-200
700R4 behind small block
- Standard 168-tooth
- Stock: $40-80
- HD: $80-150
TH400 behind big block
- Standard pattern
- Stock: $50-100
- HD: $100-200
- Race: $200-500
TH400 behind small block
- Standard pattern, often interchanges
- Stock: $50-100
47RE / 48RE behind 5.9L Cummins
- Specific HD flexplate
- Stock: $80-150
- HD: $150-300
68RFE behind 6.7L Cummins
- HD flexplate from factory
- Replacement: $100-250
- HD upgrade: $200-400
Allison behind Duramax
- Heavy-duty flexplate from factory
- Replacement: $150-300
Ford 4R70W behind small block Ford
- Ford pattern (different from GM)
- Stock: $50-100
- HD: $100-200
Ford 6R80 / 10R80 behind modular V8
- OEM Ford: $80-200
- Aftermarket: $100-250
Tooth count
168 teeth (most common)
- Small block Chevy
- LS series
- 4L60E, 700R4, TH350, TH400 (small block applications)
- Most common configuration
153 teeth (less common)
- Some small block Chevy applications
- Smaller starter pinion
- Verify your starter
Specific Ford counts
- Various tooth counts depending on engine
- Verify before purchasing
Diesel applications
- Different tooth counts
- Verify with engine spec
Always verify tooth count for your specific engine and starter combination.
Installation tips
Torque spec
Flexplate-to-crank bolts: typically 60-75 ft-lb (verify service manual)
Converter-to-flexplate bolts: typically 35-45 ft-lb (verify service manual)
Use new bolts
Always use new flexplate bolts (manufacturer recommended). They're stretched on initial torque.
Verify balance
- 153T and 168T may have different balance characteristics
- Match factory balance (internal vs external balance)
- Wrong balance = vibration
Internal vs external balance:
- Small block Chevy: Internal balance (no counterweight on flexplate needed)
- Big block Chevy: Internal balance
- LS engines: Internal balance
- Some Ford engines: External balance (counterweight on flexplate required)
Wrong balance = severe vibration. Verify with engine manual.
Torque converter bolt sequence
Hand-tighten all bolts first. Then torque in cross sequence. Verify converter is fully seated before torquing.
Brand recommendations
Standard OEM-quality
- ACDelco
- Motorcraft
- Mopar (for Cummins)
- GM / OEM equivalent
HD aftermarket
- ATP
- Pioneer
- Dura-Bond
Race / SFI-rated
- ATI
- TCI
- Hays
- BTE Performance
Billet race
- ATI billet
- TCI billet
- Inglewood Transmission
Cost summary
DIY replacement:
- Flexplate: $40-400 depending on grade
- New bolts: $15-30
- Gasket (if changed during related work): $10-40
- Total: $65-470
Shop replacement:
- Parts: $50-400
- Labor (trans must come out): $400-800
- Total: $450-1,200
Usually flexplate is replaced as part of other work (trans rebuild, converter replacement), keeping labor cost down.
Common installation mistakes
Mistake 1: Wrong tooth count
Doesn't match starter. Won't engage properly.
Mistake 2: Wrong balance
Internal vs external mismatch = vibration.
Mistake 3: Bolt sequence
Wrong sequence = warped flexplate.
Mistake 4: Wrong torque
Under-torque: loosens. Over-torque: damaged bolts/flexplate.
Mistake 5: Reusing bolts
Stretched bolts don't have same clamping force.
Mistake 6: Not verifying converter seating
Converter must fully engage with input shaft before flexplate bolts go in. Otherwise pump damage.
Mistake 7: Cheap eBay flexplate
Inferior steel, poor balance, short life.
When to upgrade to HD or race flexplate
Stay with stock if:
- Daily driver
- Stock power
- No race / track use
Upgrade to HD if:
- Tow rig
- Performance daily driver
- Higher torque application
Upgrade to race if:
- Drag race
- Sled pull
- Race-class requirement (SFI certification)
- 600+ HP applications
What we sell
OEM-quality flexplates from ACDelco, Motorcraft, Mopar, and quality aftermarket brands. HD aftermarket options for tow and performance. SFI-certified race flexplates from ATI, TCI, and Hays. Plus new flexplate bolts.
Need a flexplate? Shop our flexplate catalog. Stock, HD, and race flexplates for every common engine and transmission combination. Free shipping over $70.
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