4T40E Input Drum

If your Chevrolet Cavalier, Malibu, Cobalt or HHR, Pontiac Sunfire or G5, Oldsmobile Alero or Saturn Ion has a 4T40E that slips or will not pull in Reverse, and the teardown shows a cracked or scored drum, this is the part you are looking for. It is a used, cleaned and inspected GM reverse input clutch drum for the 4T40E and 4T45E, the drum that rebuilder catalogs list as the reverse input clutch drum with sprag, three-clutch style, for 1995-up units. Our photo shows the drum with its reverse clutch plates and retaining ring.

What the reverse input drum does in a 4T40E

In the 4T40E the reverse input drum sits right behind the driven sprocket support, separated from it by a plastic 8-tab thrust washer. It does two jobs. First, it is the housing for the reverse clutch: a bonded inner and outer piston, a return spring and retainer, three .070 in. frictions, three .088 in. steels plus one waved steel, and a selective pressure plate held in by a snap ring. Reverse clutch apply oil comes through the driven sprocket support and between sealing rings into the drum. Second, the drum carries the 22-element input sprag on its outer race, the one-way clutch that ties the input side of the geartrain together in the forward ranges. A front and rear bushing locate the drum on its shaft and support.

Because the reverse clutch is a small three-plate pack, it has little margin. Any pressure loss at the piston, the bushings or the sealing ring lands shows up as a slipping or delayed reverse long before the forward ranges complain.

Symptoms of a worn reverse input drum

• Delayed engagement into Reverse, or Reverse that flares and slips on a hill.
• No Reverse at all while every forward range still drives.
• Burnt reverse frictions and metal on the pan magnet, especially from worn drum bushings.
• Scored or grooved sealing ring lands, or a cracked drum found on the bench.
• Drive problems after a rebuild when a worn input sprag was reused; a good sprag must lock one way and freewheel the other.

How to confirm before you buy

Check the fluid level and condition first. A low level or a sticking pressure control solenoid can mimic a slipping clutch, so scan for codes, then run a line pressure test in Reverse. Our transmission pressure testing guide covers the ports and what low readings mean, and the slipping diagnosis guide helps separate a clutch problem from a hydraulic one. If reverse pressure is normal and it still slips, the reverse clutch or this drum is the likely cause. On the bench, inspect the bushings for wear, the piston bore and sealing ring lands for scoring, the friction lugs for notching in the drum, and spin the input sprag by hand in both directions.

Fitment

This drum is for the GM 4T40E and 4T45E four-speed front-drive transaxle. Rebuilder catalogs list a single reverse input drum with sprag for all 1995-up 4T40E units, and the part was pulled from that family. The 4T40E and 4T45E were built across many years and calibrations, so compare your old drum side by side with ours before you install it: the spline count, the bushing size, the sprag outer race and the overall height must match. If you are unsure, send us your year, model and VIN before ordering and we will check it. Browse every part for this transaxle in our 4T40E parts collection.

Install notes

• Install new reverse clutch frictions, steels and piston seals with the drum. The bonded inner reverse piston is not reusable once it has been removed, which is one reason a 4T40E overhaul kit or a 4T40E master rebuild kit is the right companion purchase.
• Check both drum bushings and replace them if worn; loose bushings leak apply oil past the sealing rings.
• Air-check the reverse clutch through its feed passage before final assembly, then set the clutch clearance with the correct selective pressure plate. Catalogs list three plates stamped A, B and C.
• Confirm the input sprag holds in one direction only, and install its end washers and snap ring correctly.
• Fill with Dexron VI ATF, check the level hot, and run the adaptive relearn after the rebuild as outlined in our relearn guide.

Rebuilding several sections at once? Pair this drum with the 4T40E banner rebuild kit so every seal and friction in the unit is renewed together.

Does this drum fit both the 4T40E and the 4T45E?

The part comes from the 4T40E/4T45E family, and rebuilder catalogs list one reverse input drum with sprag for 1995-up 4T40E units. Units were updated over the years, so compare the spline count, bushing size and sprag race with your old drum, or send us your year and VIN to check before ordering.

What else should I replace when I install this drum?

Install new reverse clutch frictions and steels, new piston seals and the bonded pistons, and check both drum bushings. The bonded inner reverse piston cannot be reused once it is removed. Most people install it with an overhaul or master rebuild kit.

What symptoms point to the reverse input drum?

Delayed or slipping Reverse, or no Reverse while the forward gears work, are the classic signs. A cracked drum, worn bushings or scored sealing ring lands let reverse apply pressure leak away. Confirm with a reverse line pressure test before you buy.

Is the input sprag included?

This drum is cataloged as the reverse input clutch drum with sprag, and the source part was listed with the sprag. Inspect it on arrival: it should lock in one direction and freewheel smoothly in the other.

Which fluid does the 4T40E use?

Use Dexron VI ATF. Check the level hot after the rebuild, and run an adaptive relearn so the computer resets its shift pressures for the new parts.

• How to Diagnose Transmission Slipping: Complete Troubleshooting Guide
• Transmission Pressure Testing Guide: Ports, Specs, and What the Numbers Tell You
• Transmission Rebuild vs Replacement: Real Costs and How to Decide (2026)
• Adaptive Relearn After a Valve Body Swap or Rebuild