Flex Pipe

This procedure covers the replacement of the exhaust flex pipe on a 1994-2007 Dodge Ram 2500 with the 5.9L Cummins diesel engine, including disconnection from the turbo downpipe and reconnection to the exhaust system.

Warnings

Tools required

Parts

• Flex pipe assembly × 1 — Aftermarket or OEM 4" diesel flex pipe
• Exhaust flange gasket × 1 — 3-bolt turbo downpipe gasket
• Exhaust clamp × 1 — 4" band clamp or OEM replacement
• Flange bolts/nuts (if corroded) × 3 — M10 x 1.5 exhaust hardware

Preparation

1. Park vehicle on level surface and engage parking brake
2. Chock rear wheels securely
3. Allow exhaust system to cool completely (minimum 2 hours after engine operation)
4. Raise front of vehicle and support securely on jack stands at frame rails
5. Spray all exhaust fasteners with penetrating oil and allow to soak for 15-30 minutes
6. Inspect flex pipe location and identify connection points at turbo downpipe flange and clamp/flange at exhaust pipe

Procedure

1. 1

   Remove oxygen sensor if equipped
   This vehicle (5.9L Cummins diesel) is not equipped with an oxygen sensor, so no O2 sensor removal is required. Skip this step and proceed to the next.
   Torque spec

   O2 Sensor47 Nm (35 lb-ft)
2. 2

   Remove exhaust heat shields
   Remove any heat shields covering the flex pipe area by removing the mounting bolts. These may be secured to the transmission crossmember or frame. Keep hardware organized for reinstallation.
   Torque spec

   Heat Shield Bolts14 Nm (10 lb-ft)
3. 3

   Support exhaust system
   Position a floor jack with a block of wood under the exhaust pipe downstream of the flex pipe to support the weight of the exhaust system. Raise slightly to take tension off hangers and connections.
   ⚠Ensure jack is stable and will not slip. The exhaust system is heavy and can cause injury if it falls.
4. 4

   Disconnect exhaust hanger
   If there is an exhaust hanger near the flex pipe, remove the hanger bolts to allow additional movement. The rubber isolator may need to be pried off the hanger bracket. Keep bolts for reinstallation.
   Torque spec

   Hanger Bolts20 Nm (15 lb-ft)
5. 5

   Remove downstream clamp or flange
   At the rear of the flex pipe, remove either the band clamp (loosen clamp bolt completely and separate) or the flange bolts connecting to the exhaust pipe. If using a flange connection, remove all bolts and separate the joint. Clean mating surfaces with a wire brush.
   ⚠Bolts may be severely corroded. Use 6-point sockets and apply additional penetrating oil if resistance is encountered. Heat may be required for seized fasteners.
   Torque spec

   Exhaust Clamps55 Nm (41 lb-ft)
6. 6

   Remove turbo downpipe flange bolts
   At the front of the flex pipe where it connects to the turbo downpipe, remove the flange bolts/nuts or clamp as equipped. Note: connection style varies (3-bolt flange, V-band, or clamp) on 5.9L Cummins trucks—inspect and use the correct method. Work bolts evenly to prevent binding, then separate the flex pipe from the downpipe.
   ⚠These bolts are exposed to high heat and often corroded. If bolts break, the studs may need to be drilled out and replaced.
7. 7

   Remove old flex pipe
   With all connections released, maneuver the old flex pipe out from under the vehicle. It may be necessary to twist or angle the pipe to clear frame rails and crossmembers. Lower the supporting jack slightly if needed for clearance.
   ℹ️Inspect the old flex pipe for failure mode. Common failures include cracks in the flex section, separation at welds, or complete rupture indicating exhaust leaks.
8. 8

   Clean mounting surfaces
   Thoroughly clean the turbo downpipe flange and the exhaust pipe connection point using a wire brush and scraper. Remove all old gasket material, carbon deposits, and corrosion. Ensure mating surfaces are smooth and flat for proper sealing.
   ℹ️Proper surface preparation is critical to prevent exhaust leaks. Take time to ensure surfaces are completely clean.
9. 9

   Install new flex pipe at turbo flange
   Position the new exhaust flange gasket on the turbo downpipe flange. Align the new flex pipe to the turbo downpipe flange and start all three flange bolts by hand. Apply anti-seize compound to bolt threads before installation. Do not fully tighten yet.
10. 10

    Connect downstream end
    Align the rear of the flex pipe to the exhaust pipe. If using a slip-fit connection, slide pipes together ensuring adequate overlap (minimum 2-3 inches). If using a flange, position gasket and install bolts hand-tight. Adjust flex pipe position to ensure proper alignment with no binding or stress.
11. 11

    Install exhaust clamp or tighten flange
    If using a band clamp at the downstream connection, position it over the joint and tighten the clamp bolt to specification. Ensure the clamp is centered on the joint. If using a flange connection, torque flange bolts to specification in a cross pattern.
    Torque spec

    Exhaust Clamps55 Nm (41 lb-ft)
12. 12

    Torque turbo downpipe flange bolts
    Torque the three turbo downpipe flange bolts to specification in a star or circular pattern to ensure even gasket compression and prevent leaks. Verify all bolts are properly seated.
13. 13

    Reconnect exhaust hangers
    Reinstall any exhaust hangers that were disconnected. Install rubber isolators onto hanger brackets and secure hanger bolts to specification. Ensure exhaust system hangs properly with no excessive weight on any single connection point.
    Torque spec

    Hanger Bolts20 Nm (15 lb-ft)
14. 14

    Reinstall oxygen sensor
    This vehicle (5.9L Cummins diesel) has no oxygen sensor, so no O2 sensor reinstallation is required. Skip this step.
    ⚠Do not over-torque oxygen sensors as this can damage the sensor or strip the bung threads.
    Torque spec

    O2 Sensor47 Nm (35 lb-ft)
15. 15

    Reinstall heat shields
    Reinstall all heat shields that were removed, securing with heat shield bolts torqued to specification. Ensure shields do not contact or rub against the flex pipe or any moving components.
    Torque spec

    Heat Shield Bolts14 Nm (10 lb-ft)

Reassembly

1. Remove jack supporting exhaust system and lower vehicle to ground
2. Verify all tools and equipment have been removed from under vehicle
3. Double-check that all fasteners have been installed and properly torqued
4. Ensure oxygen sensor electrical connector is properly secured and routed away from hot exhaust components

Verification

• Start engine and allow to idle, listening for exhaust leaks at all connection points
• Visually inspect all joints for smoke or exhaust escaping, particularly at the turbo downpipe flange and clamp connections
• Rev engine slightly (1500-2000 RPM) and recheck for leaks under load
• With engine running, verify exhaust system is not making contact with frame, crossmembers, or driveline components
• Check that exhaust hangers are properly supporting the system with no excessive movement or sagging
• Allow engine to reach operating temperature and recheck all connections for leaks
• If oxygen sensor was serviced, verify no check engine light or O2 sensor codes are present after test drive

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