Gear swap/vibration

[Gary23]

Hoping someone can help me , i have a 2015 mustang gt , recently did a gear swap 335’s to 373’s , after doing this i noticed a vibration at 90km/h . Did a road force balance on all tires and everything came up good .car has only 23k , had absolutely no issues with my car prior to doing all this .my next guess is the drivetrain but hoping thats not the case , if anyone has any insight on what it might be plz get back to me !!!

[ZR]

It would seem we are back in the situation many peeps experienced with a solid axle '04 or older (worst in a Fox) after a gear change where mfg just barely had vibration under control and increased shaft speed pushed it up and over the edge. Many of the IRS Cobras (factory equipped with an aluminum shaft) have at least some shaft vibration in stock form but get velvety smooth after pinion angle is corrected in spite of many thinking balance must be off on factory shaft. Even at extremely high speeds (north of 250kph) you'd be hard pressed to even imagine a vibration in my own afterwards.
As for your car, was shaft re-installed in the same position relative to the pinion flange / trans? Even if it was, well worth moving the clocking one hole at a time to see if it makes any difference. Do you have any non stock / aftermarket bushings or similar in the rear?

[ZR]

If you watch the vid, along with rubber at the hanger / support bearing, shaft joins to the trans via rubber to isolate as well.


https://www.google.com/search?q=S550+mustang+one+piece+driveshaft+install ation&oq=S550+mustang+one+piece+driveshaft+install ation&aqs=chrome..69i57.8394j0j8&sourceid=chrome&i e=UTF-8#kpvalbx=1

[Gary23]

Thanks for reply , all bushings are stock and as far as i know the driveshaft was marked and lined in the normal position .

[ZR]

Back in same spot or not, well worth the effort to try reclocking in each position as some have seen an improvement.

[RedSN]

I have always marked and reinstalled the driveshaft in the same spot, but have never understood why I was doing it. What’s the theory of it causing a vibration if not installed back in the same position? Wouldn’t it be analogous to putting the wheels back on the same studs?

[hammerhead]

I would look to the least expensive areas ujoints and pinion angle as ZR suggested.

[Gary23]

Just an update guys, got the car back today, got a brand new driveshaft and still suffering the same problems, very disappointing, if anyone has any other feed back on what it can be plz help me out, one more thing I put the car up Jacks and put it up to speed without weight on the tires and same outcome.

[Slick_89_Hatch]

Who did the gear swap? Perhaps it was not set up properly.

[ZR]

Improper set up could create a noise.