Flex Pipe

Replace the flexible exhaust pipe section on the 5.9L Cummins diesel exhaust system to eliminate leaks and restore proper exhaust flow.

Warnings

Tools required

Parts

• Exhaust flex pipe assembly × 1 — Use OEM specification or aftermarket equivalent for 5.9L Cummins
• Exhaust clamps × 2 — 3 to 4 inch diameter depending on application
• Exhaust gasket kit × 1 — Flange gaskets if flex pipe has flanged connections
• Exhaust bolts/nuts × 1 — M10 or M12 exhaust hardware

Preparation

1. Park vehicle on level surface and apply parking brake firmly
2. Place wheel chocks behind rear wheels
3. Allow exhaust system to cool completely (minimum 2 hours after engine operation)
4. Raise front of vehicle using floor jack and secure on jack stands rated for vehicle weight
5. Spray all exhaust flange bolts, clamp bolts, and hanger connections with penetrating oil and allow to soak for 15-20 minutes
6. Locate the flex pipe section in the exhaust system (typically after turbo downpipe before mid-section)

Procedure

1. 1

   Access and inspect flex pipe area
   Position yourself under the vehicle with adequate lighting. Identify the flex pipe location and connection points. On the 2007 Ram 3500 Cummins, the flex pipe is typically located between the turbocharger downpipe and the intermediate exhaust pipe. Inspect both connection points to determine if they use band clamps or bolted flanges. Check nearby heat shields or brackets that may interfere with removal.
2. 2

   Support exhaust system
   Place a jack or support under the exhaust system near the flex pipe to prevent the system from dropping or shifting during disassembly. Ensure the support is stable but not applying upward pressure.
3. 3

   Disconnect forward connection
   Begin at the forward connection (turbo side). If using band clamps, loosen the clamp bolt completely using the appropriate wrench (verify nut size against the installed hardware). For bolted flanges, remove all mounting bolts working in a cross pattern. Apply additional penetrating oil if fasteners are seized. Use a wire brush to clean threads as bolts are removed. Carefully separate the connection, using a pry bar if necessary to break the seal.
4. 4

   Remove exhaust hangers
   Locate any rubber exhaust hangers supporting the flex pipe section. Use exhaust hanger pliers or a pry bar to carefully unhook the rubber isolators from their mounting points. Work methodically to avoid tearing the rubber if hangers will be reused. Note the orientation and position of hangers for reinstallation.
5. 5

   Disconnect rear connection
   Move to the rear connection of the flex pipe. Repeat the disconnection process used on the forward connection. Loosen band clamps completely or remove flange bolts in a cross pattern. Apply penetrating oil as needed. Once all fasteners are removed, carefully separate the connection.
6. 6

   Remove flex pipe assembly
   With both connections freed and hangers disconnected, carefully maneuver the old flex pipe assembly out from under the vehicle. Note the orientation and routing of the pipe for proper installation of the replacement. Inspect the condition of adjacent exhaust components for damage or excessive corrosion.
7. 7

   Prepare mounting surfaces
   Thoroughly clean all connection surfaces where the new flex pipe will mate. Use a wire brush to remove rust, carbon deposits, and old gasket material from flanges or pipe ends. Inspect for damage such as cracks or warping. For flanged connections, ensure mating surfaces are flat. Clean threads on all reusable bolts or studs.
8. 8

   Install new flex pipe
   Position the new flex pipe assembly under the vehicle, aligning it with the connection points. Ensure the flex pipe orientation matches the original installation with the flexible section positioned to allow engine movement. Install new exhaust gaskets on flanged connections if applicable. Loosely start all connection hardware (clamps or flange bolts) but do not tighten yet.
9. 9

   Align and secure connections
   With all connections loosely attached, verify proper alignment of the entire exhaust section. Ensure adequate clearance from frame members, suspension components, and body panels throughout the flex pipe area. Begin tightening connection hardware, starting with the forward connection. For band clamps, tighten evenly to the clamp manufacturer's specification (verify the exact value in service documentation, as band clamp torque is typically much lower than flange bolt torque). For flanged connections, tighten bolts in a cross pattern to ensure even seating.
10. 10

    Reinstall exhaust hangers
    Reconnect all rubber exhaust hangers to their mounting points, ensuring the exhaust system hangs at proper height with no binding or excessive tension. The system should be supported but able to move slightly to accommodate engine torque and thermal expansion.
11. 11

    Final inspection and verification
    Remove the jack or support from under the exhaust system. Perform a final visual inspection of all connections, verifying that all clamps are tight and all flange bolts are properly torqued. Check for adequate clearance throughout the exhaust run. Verify no tools or parts were left under the vehicle.

Reassembly

1. Ensure all exhaust connections are fully tightened and properly aligned
2. Verify exhaust hangers are properly seated and supporting the system
3. Double-check clearances between exhaust and all surrounding components
4. Remove jack stands and carefully lower vehicle to ground

Verification

• Start the engine and listen for exhaust leaks at both flex pipe connections. A hissing or ticking sound indicates a leak requiring re-tightening or gasket replacement
• With engine running, visually inspect flex pipe connections for any signs of escaping exhaust gases
• Allow engine to reach operating temperature and recheck for leaks as thermal expansion may reveal issues not apparent when cold
• Perform a test drive and verify no exhaust noise, rattles, or contact with vehicle components under acceleration and deceleration
• After test drive, re-inspect all connections while exhaust is hot (use caution) to ensure clamps or bolts have not loosened

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