Coil buzz gone!

From : daniel j stern

Q: little tweaks and mods to the truck making it better a little at a time. i had an odd buzzing sound not really loud just noticeable while driving my 89 d100 318tbi/auto in a straight line. going around a curve in either direction it would go away. i traced it to the ignition coil which on this year and model is mounted to the rh side of the firewall. a napa echlin rc-1 radio noise suppression condenser placed between coil primary + and ground coil buzz slightly reduced. coil moved to intake manifold had to make a sheetmetal bracket -- the two bosses that would support the coil are not in the same plane! coil buzz eliminated entirely. the 88-91 tbi 239 318 and 360 distributors dont have centrifugal or vacuum advance; its all handled by the computer. same distributor cap as used on chrysler v8s since the 1950s but different upper distributor shaft smaller o.d. solid instead of hollow. therefore different rotor smaller shank i.d.. brass contact segment at outer end of this special rotor is shortest of all rotors ever used with this distributor cap therefore largest gap between rotor and cap terminal. rotors used to get replaced when they had burned down to anywhere near this short because of sloppy spark distribution sparking within cap and resultant carnage and radio noise. napa echlin offers mo-3000 rotor with contact segment 0.060 longer than standard mo-30 rotor but cannot use mo-30 or mo-3000 in this distributor; rotor shank i.d. too large. must use mo-25 with short contact. bought an mo-3000 and an mo-25. used jewellers mini screwdrivers to pry knurled-shank rivet holding contact segments and stainless steel springs from each rotor. put a bit of loctite in rivet hole of mo-25 rotor body installed contact segment and identical spring from mo-3000. squeezed rivet into place carefully with pliers. allowed loctite to set installed new mo-2500 handmade special rotor easier starting smoother idling and much less radio noise compared to new standard mo-25 rotor. -stern .