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  #1  
Unread 01-06-2018, 03:02 PM
WSSix WSSix is offline
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Default Brake rotor centering

Should brake rotors be centered by the studs or the hub register on the axle? Just slowly working on my vibration issue before I decide to set the car on fire.

Thank you
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1979 Trans Am WS6: LT1/T56, Kore 3 C5/6 brakes, BMW 18in rims

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  #2  
Unread 01-06-2018, 06:15 PM
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The hub should index the rotor. Same with the wheel.
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  #3  
Unread 01-06-2018, 06:58 PM
randy randy is offline
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Yup both

Explain your vibration and mods
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  #4  
Unread 01-06-2018, 07:29 PM
WSSix WSSix is offline
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Thanks guys. That's what I was expecting you to say.

I found that my rotor bores are at 2.78 inches and the axle hub is 2.68 inches. This cased the rotors to drop down onto the hub when putting everything back together. I thought I was locking the rotors in eccentrically and this might be the cause of my vibration. So I got some shim stock, put it between the rotors and hub register to tighten up the slop, and that did squat to help the issue. I was so fed up I just parked the car. For all I know, the shim stock didn't stay put some how but I doubt it since it felt the exact same. Maybe I'll look at it tomorrow.

Randy, I talk about the issue in the last few pages of my build thread. There are also other threads I've started concerning the issue. If you do a search for threads started by me, I'm sure it'll come up. The simple answer is I start vibrating at 55mph and up. It's at its worst at 55-60. It's speed related not engine or rpm related. It's definitely the rear end area, confirmed via dyno, and the wheels are true, confirmed via Wheel Wizards a rim straightening company here in Atlanta. Literally, nothing I have done has had any affect on it positively or negatively. It's maddening.

Thanks
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Trey

1979 Trans Am WS6: LT1/T56, Kore 3 C5/6 brakes, BMW 18in rims

Holy crap! I finally have a Lat-g Build thread: http://lateral-g.net/forums/showthread.php4?t=46415
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  #5  
Unread 01-06-2018, 10:16 PM
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carkrazy1987 carkrazy1987 is offline
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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
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Last edited by carkrazy1987 : 01-06-2018 at 10:20 PM.
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  #6  
Unread 01-07-2018, 06:43 AM
WSSix WSSix is offline
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Quote:
Originally Posted by carkrazy1987 View Post
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
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Trey

1979 Trans Am WS6: LT1/T56, Kore 3 C5/6 brakes, BMW 18in rims

Holy crap! I finally have a Lat-g Build thread: http://lateral-g.net/forums/showthread.php4?t=46415
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  #7  
Unread 01-07-2018, 10:04 AM
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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.
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  #8  
Unread 01-07-2018, 11:57 AM
WSSix WSSix is offline
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Quote:
Originally Posted by GregWeld View Post
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.
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1979 Trans Am WS6: LT1/T56, Kore 3 C5/6 brakes, BMW 18in rims

Holy crap! I finally have a Lat-g Build thread: http://lateral-g.net/forums/showthread.php4?t=46415

Last edited by WSSix : 01-07-2018 at 12:01 PM.
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  #9  
Unread 01-07-2018, 01:28 PM
randy randy is offline
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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.
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  #10  
Unread 01-07-2018, 02:40 PM
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SSLance SSLance is offline
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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...
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