The 68RFE behind a Cummins 6.7L is one of the most-tuned, most-abused, most-rebuilt transmissions in the diesel world. Get the rebuild kit wrong and you're back in the trans in 30,000 miles. Here's how to do it right.
Why 68RFE rebuilds are so demanding
A stock Cummins 6.7L makes about 660-800 ft-lb depending on year. Tuned, the same engine makes 900-1,200+ ft-lb. The 68RFE was rated for stock power. Tuned applications push it well past its design limits.
Result: 68RFEs in tuned trucks fail. The question isn't if but when. And the rebuild needs to address the specific failures.
Known 68RFE weak points
1. TCC apply piston / converter shudder
68RFE TCC apply pistons crack. Causes converter shudder under load.
2. Direct clutch burn
Direct clutch sees the brunt of tuned torque. Burns up.
3. Input shaft failure
Stock input shaft twists under tuned torque. Billet input shaft is mandatory for tuned applications.
4. Valve body wear
PR valve and other valves wear in the aluminum bores.
5. Solenoid pack failure
Internal solenoid pack fails over time.
6. C clutch (overdrive) burn
Overdrive clutch sees high stress.
7. Pump bushing wear
Standard high-mile failure.
What a quality 68RFE master kit must include
Base kit:
- All gaskets and seals (Transtec or equivalent)
- All sealing rings (teflon, correct spec)
- All bushings
- Master friction set (Alto Power Pack or Raybestos for HD)
- Matched steels
- Filter
- Pan gasket (rubber for 68RFE)
- All o-rings
- Modulator if applicable
Required upgrades for any 68RFE rebuild:
- Sonnax TCC apply piston kit (mandatory)
- HD direct clutch friction pack (Power Pack or Stage-1 minimum)
- Sonnax PR valve kit
- Solenoid pack (if 100K+ miles)
- HD torque converter (always)
Required for tuned applications:
- Sonnax billet input shaft (mandatory if 800+ ft-lb)
- Extra friction plate in direct clutch where possible
- HD output shaft if available
- Performance valve body
- Race-grade torque converter rated for HP
- C clutch (overdrive) HD upgrade
Friction selection by power level
Stock 6.7L Cummins (660-800 ft-lb)
Alto Power Pack frictions
Stock-equivalent HD with margin for tow.
Mild tune (800-1,000 ft-lb)
Alto Power Pack with HD calibration
Or Raybestos Stage-1.
Tuned (1,000-1,300 ft-lb)
Raybestos Stage-1 minimum, GPZ recommended
Need premium friction material.
Race / pulling (1,300+ ft-lb)
Raybestos GPZ or specialty race frictions
HD friction is mandatory.
Torque converter selection
The torque converter on a 68RFE rebuild is critical:
Stock-replacement HD converter (light tow)
$400-700. Acceptable for stock-power 68RFE.
Performance HD converter (tow + mild tune)
$700-1,200. ATS, BD, or other quality diesel-specific converter. Higher stall, billet stator.
Race-grade HD converter (high tune)
$1,200-2,000. Race-spec from specialty diesel converter manufacturers. Critical for tuned applications.
Cheap stock-replacement converter on a tuned 68RFE = same failure you started with. Don't skip this.
Valve body strategy
Stock-replacement valve body
Acceptable for stock-power daily driver.
Sonnax-upgraded valve body
Sonnax kits address PR valve, TCC apply, accumulator wear. Improves shift quality and durability.
Performance valve body (ATS, FASS-builder builds)
Specifically calibrated for tuned diesel applications. Firmer shifts, faster lockup, optimized for power.
Recommended kits by application
Stock 2500/3500 Cummins, mild tow
- Alto Power Pack master kit
- Sonnax TCC apply piston
- Sonnax PR valve kit
- Solenoid pack (if 100K+)
- HD torque converter (basic HD)
- Total parts cost: $1,200-1,800
- Build cost installed: $4,000-5,500
- Expected life: 100,000+ miles stock-use
Mild-tune Cummins (800-1,000 ft-lb)
- Alto Power Pack master kit with HD friction calibration
- Sonnax TCC apply piston
- Sonnax PR valve kit
- Sonnax billet input shaft (if pushing power)
- Solenoid pack
- Performance HD torque converter
- Performance valve body (Sonnax-upgraded)
- Total parts cost: $2,000-3,000
- Build cost installed: $6,000-8,000
- Expected life: 80,000+ miles tuned use
Tuned Cummins (1,000-1,300 ft-lb)
- Raybestos Stage-1 master kit
- Sonnax billet input shaft (mandatory)
- Sonnax billet shafts where available
- HD pump
- HD C clutch components
- Performance valve body (race-tuned)
- Race-spec torque converter
- Extra direct clutch friction where possible
- Total parts cost: $3,500-5,500
- Build cost installed: $8,000-12,000
- Expected life: 30,000-80,000 miles depending on use
Race / sled-pull Cummins
- Race-spec frictions throughout
- Billet hard parts (input, output, intermediate)
- Race valve body
- Race-grade torque converter
- HD differential pack
- Total parts cost: $5,500-10,000
- Build cost installed: $12,000-20,000
- Expected life: Short, this is race equipment
Brand recommendations for 68RFE
Alto
- Power Pack frictions specifically calibrated for diesel
- Quality master kits
- Recommendation: Yes for stock to mild tune
Raybestos
- Stage-1 and GPZ for serious power
- Best for tuned applications
- Recommendation: Yes for tuned
Sonnax
- TCC apply piston, billet input shaft, PR valve kit
- Mandatory upgrades for 68RFE
- Recommendation: Mandatory
ATS Diesel Performance
- Builds complete tuned 68RFE units
- Valve bodies and converters
- Recommendation: Yes for tuned applications
BD Diesel
- Performance torque converters and valve bodies
- Diesel-specific HD builds
- Recommendation: Yes
Suncoast Converters
- High-end diesel torque converters
- Race-grade for serious power
- Recommendation: Yes for tuned
Mopar (OEM)
- OEM 68RFE parts available
- Reliable but expensive
- Recommendation: Yes for OEM-spec rebuilds
Common 68RFE rebuild mistakes
Mistake 1: Stock parts in tuned trucks
The most expensive mistake. Stock-spec 68RFE rebuild + tuned Cummins = failure in 20,000-30,000 miles. Plan for HD parts from day one.
Mistake 2: Cheap torque converter
The torque converter does more work than any other part in a 68RFE under tow. Cheap converter = early failure regardless of rest of build.
Mistake 3: Skipping billet input shaft
For any tuned Cummins, billet input shaft is mandatory. Stock shaft will twist.
Mistake 4: Wrong friction grade
Diesel torque demands HD friction. Stock-equivalent frictions burn fast.
Mistake 5: Skipping valve body upgrade
68RFE valve body wears predictably. Sonnax-upgraded or race valve body extends life significantly.
Mistake 6: Ignoring cooler upgrade
68RFE in tow rig needs aggressive cooling. External cooler upgrade is mandatory for tow applications.
How to spec a 68RFE rebuild for your specific application
Step 1: Know your power level
Stock? Tow tune? Daily driver tune? Race?
Step 2: Match the build
Stock parts for stock power. HD parts for tow. Race parts for race. Don't over-build (waste of money) or under-build (early failure).
Step 3: Don't skip the support parts
Cooler, valve body, converter — these aren't optional add-ons. They're part of the rebuild.
Step 4: Plan for tuning
If you tune after the rebuild, the trans needs to be built for the tune. Tell your builder upfront.
What we sell
Master rebuild kits with Alto Power Pack and Raybestos Stage-1 frictions, Sonnax billet input shafts and PR valve kits, ATS and BD performance valve bodies, Suncoast torque converters, and OEM-spec replacement solenoid packs.
Ready to build your 68RFE right? Shop our 68RFE catalog. HD master rebuild kits, billet input shafts, performance valve bodies, race-grade torque converters. Free shipping over $70. Same-day ship in-stock.
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