It is not needed. Many people do away with them when they go bad. They are supposed to help with resonance noise around 2K RPM. I have not heard anyone say the extra exhaust noise was to objectionable.

Stephen

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85 300D 305K miles WVO(105K so far), Mine
82 300SD 235K miles BIO-D, Wifes
96 F250 SC PSD 4X4 285K MILES BIO-D, Ours
89 BRONCO 182K MILES sold
Finally Compression Ignition Only!