Cummins/Onan — Gear Case Disassembly
Repair & overhaul · Gear case / gear box
From a Cummins/Onan service manual covering: 15.0YD-3G, 20.0YD-3G, 20.0YD-5DG, 25.0YD-3G, 25.0YD-5DG, 30.0YD-3G, 30.0YD-5DG, 6.0-3CS1, 7.5-3CS1. Check it applies to your exact model before use.
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Before you start
- Use a new gear case gasket when gear case plate is assembled.
- Old seal must be replaced with a new seal when reassembled.
Procedure
- Remove PTO guard by loosening three 5/16 x 1/2-inch locking screws.
- Remove gear case drain plug and allow oil to drain.
- Remove six 5/16 x 1-inch capscrews and two 5/16 x 1-1/2-inch capscrews and gear case plate.
- If necessary, remove seal and snap ring from around input shaft.
- Block up gear case plate and tap PTO shaft out of plate.
- Remove snap ring and tap bearing through gear box plate.
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Source: Cummins/Onan service manual. Steps and values are as documented; always cross-check against the official manual and any later revisions for your exact serial number before servicing.