Steve Gooch’s twin-turbo Thun­der­bird should be a pretty fa­mil­iar sight to read­ers, and we’d go so far as to call it the coolest Thun­der­bird in the coun­try. With the power its twin-turbo 416ci Wind­sor was mak­ing, Steve en­coun­tered no end of is­sues, and, af­ter me­thod­i­cally work­ing his way through them, he was left scratch­ing his head at a per­sis­tent driveline vi­bra­tion at the top end of the dragstrip, around 190kph and up.

Af­ter even more re­search, he came to the con­clu­sion that his two-piece driveshaft was the cause of the prob­lems, but do you think he could find any in­for­ma­tion about the op­ti­mal set-up for two-piece drive­shafts? Nope — as they’re pri­mar­ily the re­serve of new ve­hi­cles, op­ti­mal uni­ver­sal-joint op­er­at­ing an­gles are sorted dur­ing ve­hi­cle de­vel­op­ment. In an af­ter­mar­ket ap­pli­ca­tion, like Steve’s, the best you can re­ally do is ed­u­cated guess­work.

“I’d been chas­ing a high-speed vi­bra­tion af­ter the drags and found a re­ally good web­site. If you google ‘Spicer driveshaft tor­sional anal­y­sis’ there is a cool cal­cu­la­tor,” Steve ex­plains. “Driveshaft an­gles, espe­cially on a two-piece, are like rocket science. I could not find any good info un­til I found that Spicer page.”

The in­for­ma­tion he dis­cov­ered was enough to help him get to the bot­tom of the is­sue, as you’ll see.

Steve pur­chased a dig­i­tal pro­trac­tor on­line, which was nec­es­sary to ac­cu­rately iden­tify all the an­gles in­volved in the driveline. The an­gles and mea­sure­ments re­quired are listed at left, and all an­gles and slopes should be iden­ti­fied from the driver’s (left) side of the ve­hi­cle.

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