New gears... vibration??

[dzwestwindsor]

Hi everyone, first post here. I got new 3.73 FRPP gears installed on my 2017 3.7L. I also had to get a new diff so the new ring and pinion could be installed (stock diff for 3.15 do not fit 3.73s).

However, now I get a vibration above 45ish mph. I went back to the shop and ran it on the lift, and they noticed that one of the half-shafts was vibrating and also could hear a grinding noise from under the car. They think the new diff (spider gears) is defective. Could this be the case??

Thanks in advance

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[cbrookre]

Not sure, you might get a better answer from those that spend more time in the drivetrain part of the forums

 

[Shifting_Gears]

I would have them pull the cover and re check the pinion depth. Did they replace any bearings while they were doing the swap?

The gear install could also be fine but potentially the increase in ratio has caused the driveshaft to become unbalanced because it’s seeing a much higher rotational speed. I’m not sure with the V6’s the specs on the driveshaft and how they respond to higher hearing.

 

[cbrookre]

Also, if I remember correctly, the V6 has a 1 piece drive shaft where the EB and GT have 2 piece. At least in the previous gen, the V6 driveshaft was susceptible to vibration and failure above a certain speed. Not saying that is definitely what is happening, just that it could be a possibility worth investigating. Others may have more first hand experience.

 

[dzwestwindsor]

Thanks guys. I put my car on jackstands and noticed that the yellow mark on the driveshaft doesn't line up with the yellow mark on the pinion flange (see picture). I read in another forum that Ford put them there so the driveshaft and pinion can be lined up to minimize vibration. I guess the mechanic who did my gears didn't line it back up.

I took my car to the shop and rotated the driveshaft relative to the flange so the marks lined up better. The vibration was greatly reduced, but still there. Same speeds. The low drone/hum was also there. I then noticed in the picture that there's a hemispherical button-looking thing on the driveshaft. Is that supposed to be a balancing weight ? There's a circular shape on the pinion flange that looks like something similar was attached to the flange but it fell off.

Anyone know what those hemispherical shaped things are? Could it have possibly fallen off the pinion flange? Any other ideas?

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