Annoying vibration - 08 GT

[Mrods]

Hoping the suspension gurus can help here!

I had may car lowered, and recently added UPR lower control arms (poly bushings), as well as White Line relocation brackets. While while I was anticipating additional noise and vibration, the car feels like the space shuttle at 160 kph plus (all done on a perfectly legal track in my yard of course). All are torqued to spec.

I have pulled the rotor retaining clips, had the wheels re balanced, re torqued the wheels and the issue remains.

I feels like the vibration is originating in the rear end. I do have an adjustable pan hard that centered the diff when the car was dropped. There was zero vibration before I added the LCA.

The one thing that is different about the White Line relo, is they only have a bottom hole for control arm mounting. I noticed all seem to mount in the middle.

Could this have changed a pinion angle or something?? Not sure what to do next. And don't want to swap drive shafts or something as expensive as that, as I am not sure what the heck is driving the issue?

Any guidance would be appreciated. My mirror blurs and it's really noisy.

Thanks!

[NickD]

Just thinking of what we talked about on the phone, I dont think the relocation brackets would change the pinion angle, the arms distance is not changing?

[Mrods]

The only difference is these are the same length as the UPR and with the lower hole only option, I'm wondering if they do change the angle??

[ZR]

Check pinion angle.

[Mrods]

Thanks will try that. Is spec -2??

[Uncle Buck]

I've had a mild vibration up at higher a speeds too and come to think about it, it may have started around the time I installed a set of relocation brackets and LCAs. I used the bottom hole in the brackets. Thought this stuff was supposed to correct pinion angle after you're lowered....

I'll check my angle too.

[Mrods]

Certainly cheaper than a drive shaft swap, even temporarily to test! Nick had mentioned earlier that I may want adjustable UCA. May as well go for those.

Thanks all! Hopefully that's it.

[ZR]

Decent read here for two piece shafts.

http://www.cherod.com/mustang/HowTo/LCA%20_adj.htm

[Uncle Buck]

Grabbed this from Baseline Suspension in case it's helpful. I'm assuming the crankshaft method is only useful when the car has a one piece DS.


2 Methods for
Measuring Pinion Angle
Depending on who you ask the pinion angle is the angle of the pinion relative to the Crankshaft Centerline OR the Driveshaft. I prefer the Crankshaft but I have explained both procedures below.

To measure it, you will need an angle finder that has a 360degree face and uses gravity to pull the needle. These usually come with a magnetic base and are about 3-4" in diameter.

~If all the control arms have Factory bushings: Set Pinion Angle 3 degrees to 4 degrees downward.
~If all the control arms have Poly bushings: Set Pinion Angle 2 1/2 degrees to 3 degrees downward.
~If all the control arms have Solid bushings: Set Pinion Angle 1 degrees to 1 ½ degrees downward.


Method #1

1. Place angle finder on bottom of driveshaft and write down the reading.
2. Remove driveshaft.
3. Rotate the pinion so that the ujoint caps on the yoke are pointing up and down.
4. Set the angle finder on the face of the yoke where the u-bolts go through. Sometimes the face of the yoke is not perfectly flat so I lay a socket lengthwise where the ujoint caps fit then put the angle finder on the socket.
5. Read the angle and write it down.
Determine the difference between these values then decide which way the pinion needs to be rotated to achieve the proper pinion angle.


Method #2- Crankshaft/Harmonic Balancer:
1. Remove driveshaft.
2. Rotate the yoke on the rearend so that the ujoint caps on the yoke are pointing up and down.
3. Set the angle finder on the face of the yoke where the small u-bolts go through. Sometimes the face of the yoke is not perfectly flat so I lay a socket lengthwise where the ujoint caps fit then put the angle finder against the socket.
4. Read the angle and write it down.
5. Next, hold the gauge against the front of the Harmonic Balancer. This is perpendicular to the Crankshaft so makes a great place to measure the angle from. Write down this number.
Determine the difference between these values then decide which way the pinion needs to be rotated to achieve the proper pinion angle.

[Mrods]

Gents, appreciate the info! Seems simple enough after that excellent read. I do suspect my angle is slightly off and hopefully I can adjust and get rid of that vibration.

Will let you know how it goes.

Cheers