Cummins 3970305 — Genuine Timing Gear Housing (Gear Case) for ISB 5.9L

MPN: 3970305  |  Also Known As: timing gear case housing, gear housing, gear case  |  Replaces: 3970303, 3970304

Genuine Cummins gear housing that supports and encloses the cam and crank timing gears while providing precise sealing surfaces for the front cover and block. Direct-fit for 2003–2007 5.9L ISB common-rail Ram. Ideal when the original case is cracked, warped, or oil-soaked and won’t seal properly.

Features & Benefits

• OE casting and machining for perfect alignment of timing components.
• Correct dowel/bolt locations to maintain factory geometry and seal compression.
• Sealing surfaces match OEM gaskets and RTV callouts for leak-free service.
• Direct replacement—no modifications required when used on listed applications.
• Cummins quality for long-term durability and reliability.

Verified Fitment (Automotive)

Industrial/Off-Highway: Used primarily on Tier 3-era 5.9L ISB/QSB engines; verify by ESN for equipment fitment.

Specifications

• Type: Timing gear housing (gear case)
• OE Part Number: 3970305
• Supersession / Replaces: 3970303, 3970304
• Related/Alternate Casting Seen: 3970306 (verify by ESN/build)
• Quantity Required: 1 per engine (sold individually)

Often Paired With

• Front cover gasket: Cummins 3918673 (gear case to front cover)
• Front crank seal: Cummins 3804899 (’03–’18) or seal + wear sleeve kit 3802820
• Front timing cover (separate component): Cummins 4935569 (’03–’18)

What’s In The Box

• (1) Genuine Cummins Timing Gear Housing (3970305)
• Gaskets, seals, and front cover are sold separately (see “Often Paired With”).

Installation Tips

• Clean and inspect block mating surface; check dowel alignment before torquing.
• Use new gaskets/sealant per Cummins procedure; follow the specified torque sequence.
• Always install a new front crank seal when the cover/housing is disturbed.
• Recheck for leaks and verify oil pressure on first heat cycle.

FAQ

WILL THIS FIT MY 2003–2007 5.9L CUMMINS RAM?

Yes—3970305 is the OE gear housing for most 2003–2007 5.9L ISB common-rail Ram 2500/3500 applications (confirm by VIN/ESN).

IS THIS THE FRONT COVER?

No. This is the gear housing (gear case) that mounts to the engine block. The front timing cover bolts to this housing and is sold separately.

WHAT GASKETS/SEALS DO I NEED?

Common pairings include front cover gasket 3918673 and front crank seal 3804899 (or kit 3802820 with wear sleeve). Replace these during installation.

DOES 3970305 REPLACE OTHER NUMBERS?

Yes—3970305 commonly supersedes 3970303 and 3970304 on ISB 5.9L applications.

WHAT ABOUT INDUSTRIAL ENGINES?

3970305 is used primarily on Tier 3 5.9L ISB/QSB engines; verify by ESN for non-automotive equipment.