Allison 1000 vs 68RFE vs 6R140: Diesel Transmission Comparison

The three major diesel HD transmissions: Allison 1000, Dodge 68RFE, and Ford 6R140. Different design philosophies, different strengths. Here's the comparison.

Allison 1000 (Duramax)

Years and applications:

Gears:

  • 6-speed automatic
  • Wide gear spread
  • Lower 1st for tow

Stock capacity:

  • ~620 ft-lb factory
  • Strongest stock among diesel options

Strengths:

Weaknesses:

Premium fluid required:

  • Allison Transynd
  • Specific spec

68RFE (Cummins)

Years and applications:

Gears:

  • 6-speed automatic
  • Different gear spread vs Allison

Stock capacity:

  • ~560 ft-lb factory
  • Adequate for stock Cummins

Strengths:

Weaknesses:

Fluid:

  • Chrysler ATF+4

6R140 (Ford)

Years and applications:

  • 2011-2019 (now replaced by 10R140 in some)
  • 6.7L Power Stroke
  • Some 7.3L gas applications

Gears:

  • 6-speed automatic
  • Lower 1st gear for tow

Stock capacity:

  • ~600 ft-lb factory
  • Between Allison and 68RFE

Strengths:

  • Modern design
  • Good factory rating
  • Tow/Haul mode features

Weaknesses:

  • Aftermarket support smaller than Allison/68RFE
  • TCC PWM apply issues
  • Cost of parts higher

Fluid:

  • Motorcraft Mercon SP (specific)

Capacity comparison

Stock factory:

  • 68RFE: ~560 ft-lb
  • 6R140: ~600 ft-lb
  • Allison 1000: ~620 ft-lb

Tuned capacity (mild):

  • 68RFE: 700-800 ft-lb (HD parts mandatory)
  • 6R140: 700-800 ft-lb (HD parts available)
  • Allison 1000: 800-900 ft-lb

Race/extreme (HD bundle):

  • 68RFE: 1,000+ ft-lb with full HD
  • 6R140: 900+ ft-lb with HD
  • Allison 1000: 1,200+ ft-lb with HD

Aftermarket support

Allison 1000:

  • Extensive aftermarket
  • Sonnax HD everywhere
  • Race-spec available
  • Most mature

68RFE:

  • Strong aftermarket
  • Sonnax, ATS, multiple specialists
  • Growing options

6R140:

  • Aftermarket developing
  • Some Sonnax options
  • Limited race-spec
  • Improving

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Rebuild cost comparison

Daily driver rebuild:

  • Allison 1000: $2,500-4,000
  • 68RFE: $2,000-3,500
  • 6R140: $2,500-4,000

HD rebuild (tow/mild tune):

  • Allison 1000: $3,500-5,500
  • 68RFE: $3,000-5,000
  • 6R140: $3,500-5,500

Race-spec build:

  • Allison 1000: $5,000-8,000+
  • 68RFE: $5,000-8,000+
  • 6R140: $5,500-9,000+

Operating temps

All three benefit from:

Diesel-specific:

Tuning behavior

Allison 1000:

  • Handles tunes well
  • TCC apply weakest link
  • Plan upgrades by HP

68RFE:

  • Input shaft + flexplate weakest
  • Multiple parts need HD upgrade
  • Sometimes called "the weak Cummins trans"

6R140:

  • Newer trans, less data
  • Sturdy factory
  • Tune-specific upgrades developing

Towing capacity

Allison 1000:

  • 18,000+ lb (HD GM trucks)
  • Best for max tow

68RFE:

  • 18,000+ lb (Ram HD)
  • Slightly less than Allison

6R140:

  • 18,000+ lb (Ford HD)
  • Competitive max tow

All three:

  • HD rebuild + cooler = much higher capability

Which to choose (if shopping for diesel)

Reliability priority:

  • Allison 1000 historically best
  • Less aftermarket dependency

Cost priority:

  • 68RFE rebuild cheapest
  • But more HD parts often needed

Performance priority:

  • Allison 1000 best HD support
  • Race builds especially

Brand loyalty:

  • Match your engine (Duramax/Cummins/Power Stroke)
  • Don't swap unless engine swap

Common HD upgrades by trans

Allison 1000:

68RFE:

6R140:

  • HD direct clutch
  • Updated valve body
  • Sonnax solutions developing

Maintenance comparison

All three:

  • 30,000 mile pan service for HD use
  • 50,000 mile for daily driver
  • Aux cooler critical
  • Quality fluid

Read our diesel tow rig setup

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