This procedure covers the removal and replacement of the flex pipe section in the exhaust system of a 2014-2018 Chevrolet Silverado 1500 with the 5.3L V8 L83 engine.

Warnings

Tools required

Parts

• Flex pipe assembly × 1 — Use OEM specification or equivalent aftermarket
• Exhaust flange gaskets × 2 — Use OEM specification
• Flange bolts (if corroded) × 4 — M10 x 1.5 x 40mm
• Exhaust clamp (if replacing) × 1 — Use OEM specification

Preparation

1. Ensure engine and exhaust system are completely cold (minimum 2 hours after last operation)
2. Park vehicle on level, solid surface and engage parking brake
3. Place wheel chocks behind rear wheels
4. Raise front of vehicle with floor jack and secure on jack stands at manufacturer-recommended lift points
5. Spray all exhaust fasteners, clamps, and oxygen sensor threads with penetrating oil and allow 15-20 minutes to soak
6. Locate the flex pipe section between the catalytic converters and the Y-pipe connection point under the transmission crossmember area

Procedure

1. 1

   Disconnect oxygen sensors
   Locate the oxygen sensors mounted in the flex pipe section or adjacent pipes. Disconnect the electrical connectors by pressing the release tab and pulling straight back. Using a 22mm oxygen sensor socket, carefully remove any oxygen sensors that are mounted directly in the flex pipe being replaced. Turn counterclockwise while supporting the sensor body to prevent wire damage.
2. 2

   Remove heat shields if present
   If heat shields are installed over the flex pipe area, remove the mounting bolts securing them to the underbody or exhaust hangers. Set heat shields aside for reinstallation. Clean mounting surfaces with a wire brush.
   Torque spec

   Heat Shield Bolts16 Nm (12 lb-ft)
3. 3

   Support exhaust system
   Position a jack stand or exhaust jack under the muffler section to support the weight of the rear exhaust once the flex pipe is disconnected. Adjust height to prevent excessive movement but allow some working clearance.
4. 4

   Remove upstream flange connection
   Locate the flange connection between the catalytic converter outlet and the flex pipe inlet. Remove the two or three flange bolts and nuts securing this connection. If bolts are severely corroded, apply additional penetrating oil and use a wire brush. Separate the flanges carefully and remove the old gasket.
   ⚠Flange bolts may break due to corrosion. Be prepared to use bolt extractors if necessary.
   Torque spec

   Flange Bolts45 Nm (33 lb-ft)
5. 5

   Remove downstream connection
   At the rear of the flex pipe, locate either a flange connection or band clamp joining the flex pipe to the intermediate pipe. If a flange connection, remove the flange bolts as in the previous step. If a band clamp is used, loosen the clamp bolts and remove the clamp completely. Separate the connection.
   Torque spec

   Flange Bolts45 Nm (33 lb-ft)

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

   Disconnect exhaust hangers
   Identify the rubber exhaust hangers supporting the flex pipe section. Using a pry bar or hanger removal tool, carefully work the exhaust hanger isolators off their mounting brackets. Avoid tearing the rubber isolators if they will be reused. If hanger bolts secure the brackets, remove them.
   Torque spec

   Hanger Bolts26 Nm (19 lb-ft)
7. 7

   Remove flex pipe assembly
   With all connections and hangers disconnected, carefully maneuver the flex pipe assembly down and out from under the vehicle. The pipe may need to be rotated or angled to clear frame members and crossmembers. Inspect the removed pipe to confirm failure location and type.
8. 8

   Clean mating surfaces
   Thoroughly clean all flange mating surfaces with a wire brush to remove old gasket material, carbon deposits, and rust. Ensure surfaces are flat and free of debris. Inspect flanges for warping or damage. Clean oxygen sensor ports if sensors will be reinstalled.
9. 9

   Install new flex pipe assembly
   Position the new flex pipe assembly under the vehicle, routing it through the same path as the original. Align the flex pipe so that both upstream and downstream connections are accessible and properly positioned. Temporarily support with the exhaust jack.
10. 10

    Connect exhaust hangers
    Install the rubber exhaust hanger isolators onto their mounting brackets. Ensure hangers are fully seated and the exhaust is properly supported. If hanger bolts were removed, reinstall them and torque to specification. Verify the exhaust system has proper clearance from the driveshaft, frame, and fuel lines.
    Torque spec

    Hanger Bolts26 Nm (19 lb-ft)
11. 11

    Install upstream flange connection
    Place a new exhaust flange gasket between the catalytic converter outlet and flex pipe inlet flanges. Align the bolt holes and insert new or cleaned flange bolts. Install nuts finger-tight, then torque in a crisscross pattern to specification to ensure even gasket compression.
    Torque spec

    Flange Bolts45 Nm (33 lb-ft)
12. 12

    Install downstream connection
    Install a new gasket at the downstream flange connection or position the new band clamp around the slip joint. If using a flange, torque bolts in a crisscross pattern to specification. If using a band clamp, ensure proper alignment of pipes before tightening clamp to specification.
    Torque spec

    Flange Bolts45 Nm (33 lb-ft)

    Exhaust Clamps55 Nm (41 lb-ft)
13. 13

    Reinstall oxygen sensors
    Apply a thin coat of anti-seize compound to the threads of the oxygen sensors (avoid getting anti-seize on the sensor tip). Thread sensors by hand into their ports in the new flex pipe or adjacent pipes. Torque to specification using the oxygen sensor socket. Reconnect electrical connectors, ensuring they click into place securely.
    Torque spec

    O2 Sensor60 Nm (44 lb-ft)
14. 14

    Reinstall heat shields
    If heat shields were removed, position them back in their original locations and install mounting bolts. Torque heat shield bolts to specification. Ensure shields do not contact the exhaust pipe directly and have proper clearance.
    Torque spec

    Heat Shield Bolts16 Nm (12 lb-ft)

Reassembly

1. Remove exhaust support jack and verify all connections are tight
2. Check that exhaust system has at least 1 inch clearance from all driveline components, fuel lines, and electrical wiring throughout its length
3. Verify all oxygen sensor connectors are properly seated and routed away from heat sources
4. Lower vehicle from jack stands safely

Verification

• Start engine and allow to idle. Listen for exhaust leaks at all connection points. A hissing sound indicates a leak that must be corrected
• With engine running, visually inspect all connections for escaping exhaust gases (may appear as heat waves)
• Rev engine to approximately 2000 RPM and maintain for 10 seconds while listening for leaks or abnormal sounds
• Check that exhaust system does not contact frame, driveshaft, or body components during engine movement
• After a short test drive, re-inspect all connections and verify oxygen sensor codes have not set using a scan tool if available
• Allow exhaust to cool and re-check torque on all accessible fasteners after first heat cycle

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