Brake rotor centering

[carkrazy1987]

unfortunately rear end vibrations can be a number of issues. u-joint angles, wheel tire combo, brakes, axle itself.

you said you had the rims checked, was that with tires installed (good balance)?
rotate the wheels front to back if possible?
double check all drive line angles.
if you do believe it is brake related, can you safely put rear on jack stands (weight of vehicle on axle) and accelerate to 55-60mph, see if vibration there. then slowly start removing parts and retesting. remove wheels, install lugnuts, torque to specs and check for vibration. remove rotors (ziptie block of wood in caliper not to blow out pistons), and see if vibration still there.
if still there, vibration maybe within axle, or drive shaft.

also vibration is worse between 55-60mph, does it dissipate or get worse with more mph? if the vibration intensity is matched at 110-120mph you would be looking at u-joint area for binding

[WSSix]

Originally Posted by carkrazy1987

unfortunately rear end vibrations can be a number of issues. u-joint angles, wheel tire combo, brakes, axle itself.

you said you had the rims checked, was that with tires installed (good balance)?
rotate the wheels front to back if possible?
double check all drive line angles.
if you do believe it is brake related, can you safely put rear on jack stands (weight of vehicle on axle) and accelerate to 55-60mph, see if vibration there. then slowly start removing parts and retesting. remove wheels, install lugnuts, torque to specs and check for vibration. remove rotors (ziptie block of wood in caliper not to blow out pistons), and see if vibration still there.
if still there, vibration maybe within axle, or drive shaft.

also vibration is worse between 55-60mph, does it dissipate or get worse with more mph? if the vibration intensity is matched at 110-120mph you would be looking at u-joint area for binding

I appreciate the response. I've checked all of those components multiple times. That's what is so frustrating, nothing changes with any of my adjustments. It's not on or off throttle dependent either only speed.

I've put the car on jack stands before but the vibrations were minimal compared to on the road. I put the car on a dyno to verify it was the rear area of the car for that reason.

Thank you

[GregWeld]

Check the following:


PINION ANGLE / Working angle


Driveline slip yoke - or more correctly - the length the slip yoke and it's engagement in the transmission.

[WSSix]

Originally Posted by GregWeld

Check the following:


PINION ANGLE / Working angle


Driveline slip yoke - or more correctly - the length the slip yoke and it's engagement in the transmission.

This is an area I think could/should be improved. I have a good bit of slip yoke engagement now, but to be more correct, I need maybe 3/4" more engagement. I wasn't wanting to just throw parts at the car, but I'm starting to get there because I'm seriously fed up and starting to look at E34 BMWs, lol.

Thanks Greg.

[randy]

Did you get your driveshaft shortened?

Call up the driveshaft shop. They will build you a 3 1/2 aluminum driveshaft for around $450. This fixed my vibration issues the same ones you are describing. They are 1 of 3 shops in the US that balance the driveshaft high-speed. I have 1/4" slip yoke sticking out now past the t56 magnum dust boot.

I was getting vibration around 50 and it got alot worse 70 plus. Old steel driveshaft was double checked for balance and I couldn't figure it out. I did what unmentioned above and it fixed it. Also ask for the antivibration dampened option.

[SSLance]

Really does sound like the drive line vibration issue I chased...which I finally fixed with a 3.5" steel driveshaft. My car originally came with a 2.5" shaft and the drive shaft shop said they wouldn't build a 54" driveshaft in anything less than 3.5"...said they'll "noodle" at speed if not big enough diameter.

Hope you find it...I hate vibrations...

[ProTouring442]

You're running BMW wheels, yes? The wheels should be mounted "hubcentric" (indexed on the hub), and given the difference in bolt pattern between GM and BMW...

Know anyone with a set of GM wheels you can borrow?

[WSSix]

Originally Posted by ProTouring442

You're running BMW wheels, yes? The wheels should be mounted "hubcentric" (indexed on the hub), and given the difference in bolt pattern between GM and BMW...

Know anyone with a set of GM wheels you can borrow?

I have hub and wheel centric adapters from Motorsport-Tech/BORA to correct the bolt circle and hub diameter differences. I've also removed the adapters and bolted the wheels directly to the car since the bolt pattern difference is very minor. There was no change in the vibration even though I could only center the wheel using the lugs.

Originally Posted by randy

Did you get your driveshaft shortened?

Call up the driveshaft shop. They will build you a 3 1/2 aluminum driveshaft for around $450. This fixed my vibration issues the same ones you are describing. They are 1 of 3 shops in the US that balance the driveshaft high-speed. I have 1/4" slip yoke sticking out now past the t56 magnum dust boot.

I was getting vibration around 50 and it got alot worse 70 plus. Old steel driveshaft was double checked for balance and I couldn't figure it out. I did what unmentioned above and it fixed it. Also ask for the antivibration dampened option.

Yes, factory driveshaft was shortened back in 09 when I did the LT1/T56 install. I had a good, local company do the work. I didn't have the vibration issue until 2014. Shaft length was perfect until I put the new suspension on the car. That raised the rear a little which caused the length needed to change. Problem is, I did more than just the suspension at one time. I also can't remember at this point if I had this vibration before I changed to the 3.90 gears which would change shaft speed. I also had other vibrations like tires being old and out of balance and a u-joint not perfectly secured that I found during my searching for a vibration solution. It seemed like I'd fix one thing only to realize it was only part of the issue. This current issue just won't go away.

I appreciate the insight. I was considering them or Denny's. I was also only considering steel since I'm no race car. I've had my drive shaft balance checked by multiple shops and it came back perfect each time. U-joints are good too which is why I say the yoke stick out is the only thing not perfect.

Originally Posted by SSLance

Really does sound like the drive line vibration issue I chased...which I finally fixed with a 3.5" steel driveshaft. My car originally came with a 2.5" shaft and the drive shaft shop said they wouldn't build a 54" driveshaft in anything less than 3.5"...said they'll "noodle" at speed if not big enough diameter.

Hope you find it...I hate vibrations...

I'm going to measure soon but I think I'm close to 54 inches. Maybe it's 45. I can't remember. It's the factory shaft with 3R u joints whatever it is. Plenty strong enough for the power and I don't run road courses so every thing I've read is it's fine to use. Maybe they disagree and can recommend a solution. I hate this vibration crap too. Love the power curve and drive characteristics but dear lord is this vibration ruinous to the enjoyment of the car.

Thank you all. I appreciate the responses and thoughts.