Awful vibration 80mph+
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Awful vibration 80mph+ I have had this issue since i got my 9 inch, but never got around to fixing it until now. There is a damn vibration that rattles the whole car once you get over 80mph. when you get to around 120mph it is so bad that it shakes everything in the car and my rear view mirror fell off. It ONLY vibrates when you let off the gas. If you are even slightly on it, there is no vibration at all. what gives?
I have a PST 3.5" alumnimum DS. did i buy the wrong one? i got it from EPP. Thanks for any suggestions
I have a PST 3.5" alumnimum DS. did i buy the wrong one? i got it from EPP. Thanks for any suggestions
Could be bad wheel bearings, since you got the 9inch and that being last thing you did before noticing it, does it make noise?
Have you got a chance to see if its leaking?
Have you got a chance to see if its leaking?
Last edited by LT1; May 11, 2010 at 11:46 PM.
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Sounds like a loose lower control arm. I used to have the same issue and thought it was the DS. Switched it out, with the old stock one, and it still did it. Checked a few things, and found a loose LCA bolt. Tightened it up, and the problem went away. It'd only happen at 70+, whenever I let off the gas.
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Sounds like a loose lower control arm. I used to have the same issue and thought it was the DS. Switched it out, with the old stock one, and it still did it. Checked a few things, and found a loose LCA bolt. Tightened it up, and the problem went away. It'd only happen at 70+, whenever I let off the gas.
driveshaft is too short I guarantee it 100%. I had the EXACT same problem with my pst shaft, they sent me a stock length, and a 9" needs a 1" longer shaft. get under the car and see how far out the yoke is from the output of the transmission, anything more than 1/2" and you'll get vibration.
I have a PST aluminum, correct length, DS. It vibrated horribly at 80MPH. FTR it had no balancing weights on it since it came out of the box.
I called PST and they askem me to send it to them for a checkup. It returned with a pair of balancing weights on both ends of the tube and the nasty vibe is now 95% gone. I think I may have to replace my tailshaft bushing again becuase I think the unbalanced DS might have worn it excessfully.
Do not balance it locally. Call PST, send it to them and let them check it out. They were excellent to work with and they will stand behind the product.
I called PST and they askem me to send it to them for a checkup. It returned with a pair of balancing weights on both ends of the tube and the nasty vibe is now 95% gone. I think I may have to replace my tailshaft bushing again becuase I think the unbalanced DS might have worn it excessfully.
Do not balance it locally. Call PST, send it to them and let them check it out. They were excellent to work with and they will stand behind the product.
driveshaft is too short I guarantee it 100%. I had the EXACT same problem with my pst shaft, they sent me a stock length, and a 9" needs a 1" longer shaft. get under the car and see how far out the yoke is from the output of the transmission, anything more than 1/2" and you'll get vibration.
Any link or more info that confirm this.Dont worry its not because i dont believe you but i got a vibe just a little over 70mph.Diff has been check 3 times,pinion angle is good(tested 0 degree -1 and -2 and still vibe).
So before changing my DS(yoke is about 1 inch out) i would like to be sure
nope, just personal experience I didn't believe it either, until I took the shaft to check balance and it checked out perfect. The driveshaft shop saw the wear mark on the yoke from the rear seal on the trans, and assured me that was the cause of my vibration. Called PST and they sent me a new shaft, fixed the problem.
I didn't believe it either, until I took the shaft to check balance and it checked out perfect. The driveshaft shop saw the wear mark on the yoke from the rear seal on the trans, and assured me that was the cause of my vibration. Called PST and they sent me a new shaft, fixed the problem. 
I have the same problem with mine, it started vibrating at 120 then when I changed my gears it starts at 75. Found out my driveshaft was twisted a quarter turn, got that fixed and I still have the vibration??? Anymore ideas
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Most of the time vibrations 70+ are usually caused by the drive shaft. Worst case senario, find a place with a good return policy grab a new DS then install and take it over 70 see what happens if it still vibrates send it back. 
Unless there is a way to test or get your stock DS balanced for cheap...
Unless there is a way to test or get your stock DS balanced for cheap...
TECH Resident
Joined: Jul 2007
Posts: 749
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From: Spokane, WA
Chances are if it was the pinion angle you would have the vibe a whole lot earlier than 80mph. More like 30-40 or so, at least in my limited experience anyway. It could be other things but I'd put money on a drive shaft issue. Either the balancing or being too short like wicked said.
