68RFE 300M Billet Input Shaft Ram 2500/3500 Cummins

If your 2007-2018 Ram 2500 or 3500 with the 6.7L Cummins suddenly revs with no drive in any gear, or a teardown turned up a shaft with twisted converter splines, the 68RFE input shaft is the part you are hunting for. This one is machined from 300M billet steel and replaces factory part number 68029247AA (also cross-referenced as 299600). It is built for the truck that has a tuner, bigger injectors or a heavy trailer behind it, where the stock shaft is the first hard part to give up.

What the input shaft does in a 68RFE

The 68RFE input shaft is splined to the torque converter turbine at the front and to the input clutch hub at the rear. That hub feeds the underdrive, overdrive and reverse clutches, so every gear, forward and reverse, depends on this one shaft. It also passes through the pump stator support, where its sealing rings feed clutch apply oil and lube oil through drilled passages. When the converter clutch locks at full boost, the shaft takes the whole engine torque as a sharp twisting load. Sonnax notes that input shaft failure is common as power levels go up in this unit, and the features it calls out on its own heavy duty shaft are a 300M ultra high-strength steel body, rolled turbine splines to resist twist, and extra material at the cross holes where cracks start. Those are the details to compare when you shop any billet shaft.

Symptoms of a failed or failing input shaft

• Engine revs freely in Drive and Reverse with little or no movement, often after a hard pull or a lockup event
• A clunk or bang under load, then a sudden loss of drive
• Fine steel or spline material in the pan and on the filter magnet
• Converter hub or turbine splines worn into a step, found on teardown
• Repeat failures on a tuned truck after a rebuild that reused the factory shaft

How to confirm before you buy

Check fluid level and condition first, then pull codes. Loss of drive on a 68RFE can also come from very low line pressure, a failed pump or a stuck solenoid switch valve, and none of those need a shaft. With a scan tool, compare engine speed to input speed in Neutral: the input speed sensor reads the input clutch hub that this shaft drives, so input speed near zero with the engine running points hard at a broken shaft or stripped splines. Our 68RFE input and output speed sensor guide covers how to tell a dead sensor from a dead shaft, and the 68RFE pump failure guide explains the low-pressure checks.

Fitment

Listed for the 68RFE six-speed automatic in 2007-2018 Ram 2500 and 3500 with the 6.7L Cummins turbo diesel, replacing OE 68029247AA. The 68RFE went through running changes over those years, mostly in the solenoid pack and valve body, so compare your old shaft against the new one before assembly: spline count at both ends, overall length, sealing ring grooves and the cross-drilled oil holes should all match. If you are unsure, send us your year and VIN before ordering. You can see every part we carry for this unit on the 68RFE parts page.

Install notes

• The shaft is only reachable with the transmission out and the pump removed; it comes out with the input clutch assembly. This is a bench job during a rebuild.
• This listing is the shaft only. Inspect the input clutch hub and drum splines and replace them if they are stepped. A worn hub will chew a new shaft. Confirm whether the bushing and checkball you need are on the new shaft or must be transferred.
• Install new sealing rings and check that the shaft rotates freely once the pump is torqued.
• Set front endplay. Sonnax gives the 68RFE front endplay as 0.020 to 0.030 in., adjusted with a selective thrust plate at bearing #5, and warns that the shaft normally moves 0.005 to 0.010 in. in its hub, which must not be read as endplay.
• Look hard at the converter hub splines. If they are worn, replace or rebuild the converter, or the new shaft will wear the same way.
• Refill with ATF+4 only and set the level hot.

Most owners do this shaft during a full rebuild, so it pairs naturally with a 68RFE overhaul kit and, on a truck that has been towing hot, a deep aluminum pan kit for extra fluid capacity. If you are building for power, read our 68RFE Ram 2500 Cummins common problems guide for the overdrive clutch and heat weak points worth fixing while the unit is apart.

Will this billet shaft fit my 2012 Ram 3500 6.7L Cummins with the 68RFE?

It is listed for 2007-2018 Ram 2500 and 3500 6.7L Cummins trucks with the 68RFE and replaces OE 68029247AA, so a 2012 3500 is in range. Match spline count, length and oil holes against your old shaft, or send us the VIN before ordering if you want us to check.

Do I need a billet shaft if my truck is stock?

A stock truck that tows within its rating usually lives with an OE-grade shaft. The billet 300M shaft makes the most sense when the engine is tuned, has bigger injectors or a bigger turbo, or the truck tows heavy at full lockup, which is when factory shafts twist and break.

What should I replace along with the input shaft?

Inspect and usually replace the input clutch hub if its splines are stepped, install new sealing rings, and check the converter hub splines. Most people do the shaft as part of a rebuild with a full overhaul kit, frictions and filters.

What fluid does the 68RFE use after the rebuild?

ATF+4 only. Chrysler service information for this transmission calls for ATF+4 and setting the level with the fluid hot, at 160 degrees F or more.

Can a broken input shaft be confused with a bad speed sensor?

Yes. Both can show an input speed reading of zero. A dead sensor usually still lets the truck drive in limp mode, while a broken shaft leaves no drive at all with the engine revving. Check the sensor wiring and resistance before pulling the transmission.

• 68RFE Input and Output Speed Sensor Symptoms, Testing and the P0716 Trap
• 68RFE Pump Failure: Symptoms, Diagnosis, and Replacement
• 68RFE Ram 2500 Cummins Common Problems and Fixes
• 48RE vs 68RFE: Differences, Interchange, and Which Is Stronger