If you're building a classic GM vehicle or doing an engine swap, you'll choose between the TH350 and TH400. Both are bulletproof 3-speed automatics with no overdrive. Here's the comparison.
Quick overview
TH350 (Turbo-Hydramatic 350)
- 3-speed automatic, no overdrive
- 1969-1986 production
- Compact size
- Light-medium duty
- ~450 ft-lb stock capacity
TH400 (Turbo-Hydramatic 400)
- 3-speed automatic, no overdrive
- 1964-1990 production
- Larger size
- HD applications
- ~600+ ft-lb stock capacity
Read our TH400 vs 4L80E comparison
Size and weight
TH350:
- Length: ~22 inches
- Weight: ~120 lb
- Pan: 13-bolt
- Tail housing: shorter
TH400:
- Length: ~24-28 inches (depending on tailshaft)
- Weight: ~140 lb
- Pan: 13-bolt
- Tail housing: longer
Strength comparison
Stock capacity:
- TH350: ~450 ft-lb
- TH400: ~600+ ft-lb
With HD upgrades:
- TH350: ~600 ft-lb (with shift kit, HD bands, B&M servo)
- TH400: ~1,000+ ft-lb (with billet input, HD direct, performance bands)
Applications
TH350:
- Camaro, Chevelle, Nova (most)
- C10 truck (light-duty)
- Cutlass, Monte Carlo
- Standard performance applications
TH400:
- Big-block trucks (C20/C30)
- Suburban, Blazer
- Cadillac, Buick HD
- Pontiac Trans Am
- HD towing applications
Gear ratios
TH350:
- 1st: 2.52
- 2nd: 1.52
- 3rd: 1.00
TH400:
- 1st: 2.48
- 2nd: 1.48
- 3rd: 1.00
Nearly identical in ratios. The differences are strength and design.
Cost comparison
Rebuild kit:
- TH350: $200-400 (basic to quality)
- TH400: $250-500 (basic to quality)
Reman trans:
- TH350: $1,200-2,000
- TH400: $1,500-2,500
HD performance:
- TH350 with kit: $1,500-2,500
- TH400 with kit: $2,000-3,500
Read our transmission parts buying guide for sourcing.
When to use which
Use TH350 if:
- Light/medium-duty street car
- Compact transmission tunnel
- Stock or mild-built engine
- Cost-sensitive build
- Classic restoration with TH350 original
Use TH400 if:
- HD truck or tow rig
- Big-block or supercharged
- Race/performance build with strength priority
- 4WD (T-case adapts well)
- Diesel swap
Common upgrades
TH350:
- B&M shift kit (corrects shifts, light HD)
- B&M HD servo
- HD direct clutch pack
- TransGo reprogramming kit
TH400:
- Billet input shaft
- HD direct clutch pack (extra friction)
- Sonnax pump rotor kit
- Race-spec band servo
- ATI race converter
Performance options
Both transmissions support:
- B&M shift improvers
- TransGo HD kits
- High-stall torque converters
- Reverse pattern manual valve bodies (race)
- Trans coolers (mandatory in HD)
Read our torque converter stall speed guide
Adapters and swaps
TH350 to TH400 swap (in same vehicle):
- Possible but requires crossmember mod
- Driveshaft length differs
- Bellhousing pattern same (small-block GM)
- Speedo gear differs
TH400 to 4L80E swap:
- 4L80E is electronic TH400 with overdrive
- Read our TH400 vs 4L80E comparison
TH350 to 700R4 swap:
- 700R4 adds overdrive, similar size
- Read our 700R4 vs 4L60E comparison
Choosing for your project
Hot rod / Pro-Touring:
- TH350 with shift kit for street
- TH400 for heavy power
Restoration:
- Match original (whatever came in vehicle)
- Quality rebuild over reman
Truck/tow:
- TH400 every time
- Consider 4L80E for overdrive
Race:
- TH400 with full race build
- Some classes mandate certain trans
What's in a quality rebuild
Master rebuild kit:
- All frictions (Alto Red Eagle minimum)
- All steels
- All bands
- All seals and gaskets
- All bushings
HD upgrades worth doing:
- HD direct clutch pack
- B&M shift kit
- HD band servo
- New pump rotor set
New torque converter:
- Stock replacement: $300-500
- Performance stall: $500-1,000
Need TH350 or TH400 rebuild parts? Shop our complete catalog. Master rebuild kits, B&M shift kits, HD clutch packs, performance bands, torque converters. Free shipping over $70.
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