47RE Sprag Clutch

Pulling the overdrive unit off a Ram 2500 or 3500 with the 5.9L Cummins or 8.0L V10 and the 47RE behind it? The part most rebuilders call the OD sprag is really a roller-type overrunning clutch that lives inside the overdrive output shaft, and it is cheap insurance compared with tearing the back half of the transmission down twice. This one is brand new and arrives in its factory package: two rows of rollers held in a polymer cage, each roller spring-loaded toward its locking ramp. It is the overdrive clutch only. The low-reverse roller clutch in the main case is a separate part, listed on our 47RE low-reverse outer race page.

What the overdrive roller clutch does in a 47RE

A 47RE is a three-speed main transmission with a bolt-on overdrive unit at the rear. In first, second, third and reverse, the overdrive unit has to pass power straight through at a 1:1 ratio. Two parts make that happen together: the spring-applied direct clutch and this roller clutch. The output shaft serves as the outer race and a lobed cam on the overrunning clutch hub serves as the inner race, so under drive load the rollers wedge between the two and lock the overdrive planetary. On the 3-4 upshift the overdrive clutch applies, the direct clutch is released, and the rollers ride off their ramps and freewheel. Because the roller clutch carries drive torque in three of four gears on a heavy truck that tows, it sees more work than its size suggests.

Symptoms tied to a worn overdrive roller clutch

• Noise that shows up in fourth gear only; the factory diagnosis chart lists worn or scored overdrive roller clutch rollers as a cause
• A slip or flare in first through third under heavy throttle or towing load while fourth feels solid, once the rear clutch and fluid level are ruled out
• A clunk from the back of the case on takeoff or on throttle tip-in and tip-out
• Brittle, discolored cage material or blue rollers found on teardown, signs the overdrive unit has run hot
• Overdrive clutch or direct clutch burn-up on a 47RE that tows; a roller clutch that went through that heat should not go back in

How to confirm before you buy

Most 47RE complaints that feel like an overdrive problem start somewhere else, so test before you tear down. Check the ATF+4 level hot, and look at its color and smell for signs of overheating. The factory road-test logic helps: the rear clutch is on in every forward gear, so slip in any two forward gears points at the rear clutch, while slip during the 3-4 shift or only in fourth points at the overdrive clutch. Our 47RE common problems guide walks through those checks and the overdrive lube loss that cooks this unit, and the Ram 3500 Cummins problems guide covers what towing does to it. Once the overdrive unit is on the bench, the call is easy: the factory says to replace the roller clutch assembly or the race if either is worn or damaged in any way.

Fitment

The listing covers the 1994-up A500 (42RE and 44RE), the A518 (46RH and 46RE), the A618 (47RH and 47RE) and the 48RE, because all of them share this overdrive roller clutch. For the 47RE that means Ram 2500 and 3500 pickups and cab-chassis trucks with the 5.9L Cummins or 8.0L V10. Lay your old clutch next to this one before installing and compare diameter, roller rows and the locating shoulder. If you have a swapped or rebuilt unit and are not sure what you have, send us the year and VIN. The rest of the parts for this unit are on our 47RE collection page.

Install notes

• Rollers or springs can move inside the cage during shipping. If one has shifted, press it back into its pocket by hand.
• The clutch fits on its hub only one way: the shoulder on the clutch seats in a small recess at the edge of the hub.
• Start the assembly into the output shaft with snap ring pliers expanded in the hub splines and turn it counterclockwise as you push. Never drive it in.
• Inspect the race surface inside the output shaft. It must be smooth and free of scoring, and minor marks on machined surfaces can be cleaned with crocus cloth only.
• Set the No. 3 thrust bearing between the clutch hub and output shaft, then line up the planetary and clutch hub splines with an overdrive spline alignment tool before sliding the unit onto the intermediate shaft.
• Do the job with fresh soft parts such as the 47RE banner rebuild kit, and refill with ATF+4.

Is this the overdrive sprag or the low-reverse one?

This is the overdrive roller clutch that installs inside the overdrive output shaft. The low-reverse roller clutch is in the main case and uses a different race.

Will it fit a 1996 47RE and a 2002 47RE?

Yes. It is listed for 1994-up A500, A518 and A618 units including the 47RE, plus the 48RE. Compare it with your old part, or send us your year and VIN.

Mine came out looking fine. Do I still need to replace it?

On a rebuild, yes. Spring tension loss and heat-hardened cage material are hard to see, and the factory calls for replacing the clutch if it is worn or damaged in any way.

Can I reuse my output shaft?

Only if the race surface inside it is smooth and unscored. A new roller clutch running on a damaged race will fail again.

What fluid goes back in?

ATF+4. Pre-lube the rollers and hub with ATF+4 on assembly and check the level hot in Neutral after the rebuild.

• 47RE Common Problems and Fixes
• 47RE Ram 3500 Cummins Common Problems and Fixes
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