I've been tryinh yo nail down this high mph vibration in 4th gear and up for a while now after I twisted me stock output shaft and installed a new 30 spline viper shaft. My pinion angle is set correctly at -2 degrees and I've triple checked it many times and ways to verify that. But what I get is a very bad decel off gas vibration above 80 mph. I do get a slight on gas vibe above 80 but no where near what is feels like off gas above 80. My current setup is a MWC fab 9", PST driveshaft, MWC weld in anti roll bar. Any ideas.

 

You need to start somewhere. How much backlash is in the rear end? You can check without doing much, just crawl under and twist the driveshaft back and forth with the transmission in neutral. Be sure to block the wheels first. It could be something as simple as a transmission or motor mount, or even a U Joint. Just start checking and eliminating stuff until you find it.

Al 95 Z28

 

Wouldn't mind knowing the answer to this as well..I'm thinkin its rear related somehow!!

Sam..

 

Everything checks out, I think I might recheck u-joints though.

 

Did you solve this? I am having the same issue. Mine is a s60 and I believe my driveshaft is pst too. I am thinking of going +1 for pinion. I had my pinion angle at -2 and went to -1 and the vibration went from 70 mph decel to 80 mph decel. Still stumped and about to go back to stock rear.

 

Kinda sorta solved, the driveshaft was to short in my case so I got it lengthened, still vibes real bad, ended up putting my pinion angle at almost 0, maybe -1/2 and all decel vibes are gone above 80mph, but I still have a noticeable 70-80mph back vibe that atty this point in blaming on lose gears.

 

I have this same damn problem. My car vibrates above 60. I changes axles, gears, driveshaft, balanced tires, changed pinion angles, pretty much everything and it still does it. Its an s60 with a locker

 

i have the same prob. only difference is that i dont know my pinion angle... how do i adjust that? i have a kinda like a grinding when im just below 2k rpm.. im hoping its something simple.. having the pinion angle does have its effects on the drivetrain, right?
glad u kinda fixed it hehe..