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Removing press-fit splined air compressor or accessory drive couplers on a Cummins NT, NH, or 855 diesel engine during an in-frame repair or front gear case overhaul? Follow this step-by-step professional workshop procedure to clean drive hubs, position the M20040 collet jaws, lock the retention ring, advance the forcing screw, and draw press-fit couplers off smoothly without damaging drive splines or shaft bearings.

Why Standard Jaw Pullers & Torches Damage Cummins Accessory Drives

On Cummins 855 engines, air compressor and accessory drive couplers are press-fit onto splined shafts extending from the front gear housing. Because these couplers transfer heavy rotational torque to drive air compressors and fuel pumps, their spline fit is extremely tight. Technicians who attempt removal using standard 2-jaw or 3-jaw gear pullers run into severe problems: standard puller jaws slip off the narrow coupler shoulder, chipping the outer ring or applying cocked side forces. Prying behind the hub with pry bars flexes the front gear case cover, causing oil leaks and damaging internal shaft bearings. Heating the coupler with an oxy-acetylene torch transfers intense heat down the shaft, melting front oil seals and annealing the heat-treated drive shaft splines. Utilizing the 3-pound M20040 Splined Coupler Puller completely eliminates extraction damage. Its collet jaws envelope the coupler hub 360 degrees, applying pure axial forcing screw pressure to draw the coupler off cleanly.

The 5-Step Cummins 855 Coupler Removal Protocol

1. Clean Coupler Hub & Apply Penetrating Lube: Remove surrounding air compressor plumbing or accessory drive shields. Spray shop solvent and air to clean dirt and grease off the splined coupler hub. Apply penetrating oil to the shaft interface.
2. Position M20040 Collet Jaws Around Coupler: Open the M20040 collet assembly and slide the jaws over the splined coupler hub, seating the internal puller lip squarely into the coupler outer retention groove.
3. Lock Collet Sleeve & Align Forcing Screw: Slide the outer locking sleeve over the jaws to clamp the collet 100% flush around the hub. Center the hardened forcing screw tip squarely against the dimple of the accessory drive shaft.
4. Lubricate Forcing Screw Threads & Apply Hand Torque: Apply clean engine oil to the M20040 forcing screw threads. Turn the forcing screw clockwise using a hand wrench or socket to take up tension.
5. Draw Coupler Off Shaft Smoothly & Inspect Splines: Continue turning the forcing screw smoothly. The M20040 will draw the splined coupler off the shaft linearly. Once removed, inspect shaft splines and keyways for wear before installing new components.

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