Vibration 60-80 mph with low throttle input and on decel

[UFGatorGuy20]

First, a bit about what I'm experiencing:

When I get up to ~60mph and above (have really only tested to about 80mph), I'm getting this shimmy in my seat, the pedals, and the shifter... maybe a bit in the steering wheel too. I want to say that the oscillation frequency is close to the tire rotation frequency - so it may be as simple as tire imbalance. But, the fact that it gets worse when I push the gas a bit has me thinking driveshaft or component in that stream. It does shimmy when I let off the gas, but eventually goes away as I coast to a slower speed. I also believe I'm getting the same behavior whether I'm in 4th, 5th, or 6th gear. If I just hold throttle constant it feels like it comes on for 30 seconds, then goes away, comes back, etc. Also I'm a track pack, performance pack, with 38k miles, and newer Michelin Pilot Sports. Otherwise stock suspension. The car is a dream to drive otherwise.

A lot of my searching on svtp takes me back a few generations so not specific help to the Trinity. I found a good thread on another site: http://themustangsource.com/forums/f804/driveline-vibration-65-85mph-521314/

TLR - many 2014 GT owners (not GT500) pursued a fix at the dealer under warranty. Many dealers claimed either tire balance issue, or if the driveshaft was suspect that it was still in spec. Many folks recommend a single piece carbon drive shaft, such as: http://www.americanmuscle.com/dss-cf-driveshaft-1314gt500.html - But that's $1400 for just the part alone.

I figured I'll take it in to get the tire pressure / balance / alignment checked first and go from there. Was actually planning on buying the eibach pro lowering springs, bolts, and panhard bar. So I may still just go through with that instead of having to pay for two alignments.

Just looking to see if others experienced this and solved it. :beer:

 

[Beercules]

You already have a 1 piece carbon fiber ds from the factory, so that's not it. The only problem those have had is the tag coming loose and making noises.

Sounds like alignment. Get it checked to see if that can fix it. Then check into this kit for lowering. (Lowering only will cause axle hop). Bmr are good at what they do.

http://www.bmrsuspension.com/?page=products&productid=785&superpro=0

Might also want a bump steer kit. Ask them about the uca\mount while you're at it, but they probably would have thrown it in with the kit if you'd need it.

Hopefully getting a tire balance\alignment after the lowering will fix it, if not there's lots of knowledgeable, helpful people here.

 

[Snoopy49]

You should also check the rear axles and see if one of the flanges is bent?

 

[UFGatorGuy20]

You already have a 1 piece carbon fiber ds from the factory, so that's not it. The only problem those have had is the tag coming loose and making noises.

Sounds like alignment. Get it checked to see if that can fix it. Then check into this kit for lowering. (Lowering only will cause axle hop). Bmr are good at what they do.

http://www.bmrsuspension.com/?page=products&productid=785&superpro=0

Might also want a bump steer kit. Ask them about the uca\mount while you're at it, but they probably would have thrown it in with the kit if you'd need it.

Hopefully getting a tire balance\alignment after the lowering will fix it, if not there's lots of knowledgeable, helpful people here.

Lol... See how much I don't know!

Thanks for the info. Looks like I'll try balance and alignment as part of the lowering process.

 

[UFGatorGuy20]

You should also check the rear axles and see if one of the flanges is bent?

Will check this too. No power mods so hope that's not it. But maybe still a suspect component.

 

[tomshep]

Don't add any parts until you get this solved.

Tom

 

[railroad]

You can eliminate parts of the drive line, by doing some simple test. Vibration in neutral sitting still, engine or flywheel, clutch. Pushing the clutch in, same condition, any change, clutch, flywheel. Up to speed, put in neutral, let rpm fall to idle, still shaking, tires, brakes, axles, driveshaft. If you want to investigate yourself, pull the rear wheels, after making sure they are rotating true. Bring the speed up to where it vibrates, eliminates the tires and wheels, not necessarily the axles though. Or let the alignment guy drive it, with you in the car. Good luck,.

 

[paluka21]

You can eliminate parts of the drive line, by doing some simple test. Vibration in neutral sitting still, engine or flywheel, clutch. Pushing the clutch in, same condition, any change, clutch, flywheel. Up to speed, put in neutral, let rpm fall to idle, still shaking, tires, brakes, axles, driveshaft. If you want to investigate yourself, pull the rear wheels, after making sure they are rotating true. Bring the speed up to where it vibrates, eliminates the tires and wheels, not necessarily the axles though. Or let the alignment guy drive it, with you in the car. Good luck,.

Good info railroad. :beer:

 

[UFGatorGuy20]

You can eliminate parts of the drive line, by doing some simple test. Vibration in neutral sitting still, engine or flywheel, clutch. Pushing the clutch in, same condition, any change, clutch, flywheel. Up to speed, put in neutral, let rpm fall to idle, still shaking, tires, brakes, axles, driveshaft. If you want to investigate yourself, pull the rear wheels, after making sure they are rotating true. Bring the speed up to where it vibrates, eliminates the tires and wheels, not necessarily the axles though. Or let the alignment guy drive it, with you in the car. Good luck,.

Thanks for the excellent information railroad.

It appears I have drastically improved the issue and it was very simple. So, while taking the car for another drive to perform these tests, my low pressure indicator came on. My left rear went down to ~25psi. I put it back up to 35psi and it's much smoother. I still have to perform some visuals on the tire to make sure I don't have anything in it. But, after testing and going all the way to work (~35miles) I'm still at 35psi. Some feedback on the tests I did after getting the rear tire pressure back up to spec:

1) No vibration sitting still in neutral other than exhaust burble :beer:
2) No vibration sitting still and pressing / depressing clutch
3) I got up to 80mph and decelerated to 60mph while still in 6th gear. On one or two occassions, I felt a little seat, pedal, and steering wheel shimmy going down between 75-70. But it's clean / smooth outside that small window. One set of tests going from 80-60 was like butter.
4) I got up to 80mph, let the rpm fall to idle and decelerated to 60mph while in neutral. I still felt a little seat, pedal, and steering wheel shimmy going down between 75-70. Perhaps a bit more than in step 3.
5) When I give a slight throttle input in 6th gear going from say 60-65mph, I feel the slightest shimmy in the seat / pedal, steering wheel.

Overall the ride is much smoother and I feel I just need to double check all the tires. I figure anything else may just be natural harmonics with throttle input at such low RPM in 6th gear and possibly road imperfections.

 

[railroad]

Seat shake is usually rear, steering wheel and pedals, front or engine. Have the tire checked, running low pressure is hard on the side walls. You should be OK, if was not for too long or hard driving.