The C2 clutch in the Allison 1000 carries 4th, 5th, and reverse. When it slips, your Duramax loses grunt. Here is the fix.
Symptoms of C2 clutch failure
- Slip in 4th or 5th gear under load
- Reverse slip (sometimes)
- P0732, P0733 (gear ratio incorrect)
- Burnt fluid smell
- TCM may default to limp mode
Why the C2 clutch wears out
Heavy towing:
- Allison clutches are sized for stock duty
- Heavy trailer + grade = sustained slip
- Slip = heat = clutch friction loss
Tuned Duramax:
- Stock C2 pack: ~520 lb-ft input limit
- Tuned LB7/LBZ Duramax: 600-800 lb-ft
- C2 is first failure point on tuned trucks
Old fluid:
- Allison TES-295 spec required
- Over-extended drain intervals fry the C2 first
Rebuild parts
Stock C2 clutch pack:
- 5 friction discs + 5 steels
- $80-$140 OEM
- $60-$120 Raybestos aftermarket
HD C2 clutch pack:
- 6 friction discs (added capacity)
- Carbon fiber or kevlar frictions
- $200-$350
- Required for any tuned Duramax
Also replace:
- C2 apply piston seal
- C2 return spring set
- New thrust washers
Install notes
- Trans must come out
- Major teardown required
- 8-12 hours shop labor minimum
- Pressure-test before reinstall
Cost breakdown
DIY rebuild (C2 only):
- HD C2 pack: $200-$350
- Seals + bushings: $80-$140
- Fluid (15+ qts TES-295): $250-$400
- Total parts: $530-$890
Shop rebuild (C2 only):
- Parts: $530-$890
- Labor: $1,400-$2,200
- Total: $1,930-$3,090
Full Allison rebuild:
- $3,500-$6,500 depending on HD level
Prevention
Required:
- TES-295 fluid only (no Dexron, no synthetic blend)
- 30,000-mile drain interval if towing
- 60,000-mile interval if light duty
- HD trans cooler for tuned trucks
TCM tuning:
- HD tune line pressure helps clutches survive
- Stock tune kills C2 on high-HP builds
When C2 is not enough
If the truck makes over 700 HP / 1,200 ft-lb, the C2 still slips even with HD parts. Solution:
- ATS or SunCoast triple-disc converter
- HD billet input shaft
Need Allison 1000 C2 clutch pack, full rebuild kit, or HD parts? Shop our Allison catalog. HD clutch packs, rebuild kits, billet input shafts. Free shipping over $70.
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