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.