48RE Sprag Clutch

Rebuilding the overdrive unit on a Ram 2500 or 3500 Cummins with the 48RE, or on a gas truck or Jeep with a 46RE, 47RE, 44RE or 42RE? The overdrive overrunning clutch is the small part most rebuilders call the OD sprag, and it is one of the pieces you should replace every time the overdrive unit is apart. This is a new one in its factory package. It uses twin stacks of rollers in a polymer cage, with spring loading that pushes each roller toward the lock position.

How the overdrive sprag works in a 48RE

The 48RE is a three-speed main box with a separate overdrive unit bolted on the back. Inside that unit the overdrive output shaft forms the outer race of this clutch, and a lobed cam on the overrunning clutch hub is the inner race. The overrunning clutch and the direct clutch work together in every range except fourth, locking the overdrive planetary so it turns as a unit. When the overdrive clutch applies for fourth gear, the rollers simply ride off their ramps and the clutch freewheels. That handoff is what gives the 3-4 shift its smooth overlap.

Why it wears out even when it looks fine

• The return springs lose tension with heat and miles, so rollers no longer snap into position fast enough
• The polymer cage turns brittle on a unit that has been run hot, common on trucks that tow
• Rollers and cam lobes wear where they contact, leaving flats you can miss at a glance
• Overdrive-unit heat often comes with the 48RE's known overdrive and direct clutch wear, so the two problems travel together

Symptoms and how to confirm

A tired overdrive roller clutch can show as a flare or slip under heavy load in first through third, a clunk on takeoff or on throttle reversal, or coast noise from the back of the case, while fourth gear feels normal because the clutch is freewheeling there. Rule out the obvious first: check ATF+4 level and condition hot, and verify line pressure with a gauge. Sonnax notes the 48RE raises line pressure in fourth and with the converter clutch on, so compare against 48RE values. Our 48RE Cummins transmission problems guide lays out what actually breaks in these units, and if the complaint is about when it shifts rather than how it holds, read 48RE shift solenoid symptoms first.

Fitment

Listed to fit the A500, 42RE and 44RE, the A518, 46RH and 46RE, the A618, 47RH and 47RE, and the 48RE. The 48RE was used in 2003-2007 Ram 2500 and 3500 trucks with the 5.9L Cummins. This is the overdrive unit clutch only, not the low-reverse overrunning clutch in the main case. Compare it to the old one before installing, and send us your year and VIN if you are not sure what you have. Everything we stock for the late unit is on our 48RE collection page.

Install notes

• Elements or springs can shift in the package during transit. If one has moved, push it back into its pocket before installing.
• The factory procedure installs the overrunning clutch into the output shaft with snap ring pliers expanded in the hub splines and a counterclockwise twisting motion. Do not hammer it in.
• Inspect the output shaft race and the cam lobes. A new clutch on a scored race will not last.
• Align the overdrive planetary and hub splines with an alignment tool before installing the overdrive unit on the case.
• Lubricate with ATF+4 on assembly and refill with ATF+4. While the overdrive unit is apart, the 48RE master rebuild kit covers its frictions and seals, and the 48RE clutch module is there if you need frictions on their own.

Is this the low-reverse overrunning clutch or the overdrive one?

It is the overdrive overrunning clutch, the one that fits inside the overdrive output shaft. The low-reverse overrunning clutch in the main case is a different part.

Does it fit my 47RE or 46RE?

Yes, it is listed for the A500/42RE/44RE, A518/46RH/46RE, A618/47RH/47RE and 48RE. Compare it with your old part before installing, or send your year and VIN to check.

My old one looks fine. Should I still replace it?

Yes on any overdrive-unit rebuild. Spring tension loss and brittle cage material are hard to see, and both cause the clutch to engage late.

A roller fell out of the cage when I opened it. Is it damaged?

Usually not. Rollers or springs can move during shipping; reinsert them in their pockets before installation.

What fluid should I use?

ATF+4. Chrysler specifies it for the 48RE and warns that other fluids can cause poor shift quality and converter shudder.

• 48RE Cummins Transmission Problems: Failure Points, Upgrades, and What Actually Breaks
• 48RE Shift Solenoid Symptoms: Overdrive and TCC Solenoid Testing and Replacement
• 48RE Ram 2500 Cummins Common Problems and Fixes
• 48RE Ram 3500 Cummins Common Problems and Fixes