The 2021 Ram 3500 with the 6.7L Cummins is a workhorse diesel that's largely bulletproof on the engine side, but the 68RFE automatic transmission and its supporting systems are the Achilles heel — expect mounting issues, cooler failures, and solenoid problems as miles pile on.
Transmission Mount Failure
Common · medium severityTypical onset: 40,000-80,000 mi
Symptoms: Clunking on acceleration or deceleration, Excessive driveline vibration, Visible sagging or torn rubber on mount, Transmission shifts feel harsher
Fix: Replace transmission mount and crossmember bushings. Usually 2-3 hours labor with transmission support required. OEM mounts last longer than aftermarket — don't cheap out.
Estimated cost: $400-700
Transmission Oil Cooler Line Leaks and Cooler Failure
Common · high severityTypical onset: 60,000-120,000 mi
Symptoms: Transmission fluid pooling under truck, Pink/red fluid dripping from radiator area, Overheating transmission temps, Burnt transmission fluid smell
Fix: Cooler lines corrode at fittings or cooler itself cracks internally. Requires cooler replacement and line replacement, plus full fluid flush. 4-6 hours labor. If coolant mixes with ATF, you're looking at a full transmission rebuild.
Estimated cost: $800-1,500 (cooler/lines only); $4,500-7,000 (if contamination requires rebuild)
68RFE Shift Solenoid Pack Failure
Occasional · high severityTypical onset: 80,000-140,000 mi
Symptoms: Harsh or delayed shifts, Transmission slipping between gears, Check engine light with P0750-P0770 codes, Limp mode activation, Won't upshift past 3rd or 4th gear
Fix: Solenoid pack lives inside the valve body. Pan drops, valve body removal, solenoid replacement. 6-8 hours labor. Should replace transmission filter and fluid simultaneously. Use OEM Mopar solenoids — aftermarket causes repeat failures.
Estimated cost: $1,200-2,200
Torque Converter Shudder and Lockup Clutch Failure
Occasional · medium severityTypical onset: 70,000-110,000 mi
Symptoms: Vibration at 40-50 mph during light acceleration, Shudder feels like driving over rumble strips, Slipping on highway acceleration, Transmission overheating
Fix: Torque converter lockup clutch wears or fluid contamination causes shudder. Requires transmission removal and converter replacement. 10-14 hours labor. If caught early, sometimes a fluid and filter change with Mopar additive buys time, but converter replacement is inevitable.
Estimated cost: $2,500-4,000
Overdrive Solenoid and Governor Pressure Issues
Occasional · medium severityTypical onset: 90,000-150,000 mi
Symptoms: No overdrive — stuck in 4th gear, RPMs stay high on highway, P0871 or P0845 trouble codes, Erratic shift points
Fix: Overdrive solenoid or governor pressure solenoid fails. Valve body removal required. 5-7 hours labor. Often combined with full solenoid pack refresh if one has failed.
Estimated cost: $900-1,600
Fuel Filter Head Leaks and Water-in-Fuel Sensor Corrosion
Common · low severityTypical onset: 50,000-100,000 mi
Symptoms: Fuel smell near driver-side frame rail, Visible diesel weeping from filter housing, Water-in-fuel warning light intermittent or stuck on, Hard starting in cold weather
Fix: Filter head O-rings degrade or water sensor corrodes. Replace fuel filter assembly and O-rings. 1-2 hours labor. Use OEM Mopar filters — aftermarket heads crack.
Estimated cost: $250-450
Buy the Cummins, budget for the transmission — it's a $50k+ truck that needs a $2k transmission refresh every 100k miles, but the engine will outlast two transmissions if maintained.
AI-assisted summary drawn from NHTSA recall data, our labor-times database, and platform knowledge. Not a substitute for a pre-purchase inspection on a specific vehicle.