Rear end slight shift at acceleration

rekabs

TWERK
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#1
I've noticed when I accelerate fairly hard while cruising in the Cobra I have the slight feeling of the rear end of the car shifting to the right a little bit. Any ideas what might cause this? I have a Backdraft. I don't feel anything when I cruise at constant speed. No slipping of tires during the acceleration.
 

Hotfingrs

Running mid to low 9's All Motor Best ET 9.14
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#3
Every time I had the feeling, it was a half shaft about to go. Check your driver's side.
 

Scott Harrison

"Growing old is mandatory, growing up is optional"
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#4
BACKDRAFT COBRA:
  1. Check the nut between the steering wheel and seat: (If the tires break loose-which is particularly easy with summer tires in the cold, the rear will naturally crab to the right.)
  2. Check tire pressures
  3. Check lugnuts
  4. Check for loose wheel bearing
  5. Check for worn CV joint
  6. Check alignment (http://www.capitalareacobraclub.com/index.php?threads/bdr-owners.13511/)
 
Last edited:

Scott Harrison

"Growing old is mandatory, growing up is optional"
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#6
Cold tires won't make much noise, and the side pipes will drown it out.
 

Scott Harrison

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#7
Physics lesson.....from the WEB:

During hard acceleration, there is also a weight transfer from side to side across the axle based on the prop shaft direction of rotation and torque reaction. We refer to this as tire jacking. Since our reference point is the ground and the wheels are attached to the ground, it may seem difficult to see what is happening. It is actually quite easy to see what is occurring, but the explanation seems backward. We see the right side of the vehicle squat down during hard acceleration. The right wheel is being pushed upward toward the vehicle body. However, since the wheels do not leave the ground and the ground is our frame of reference, it appears that the right corner of the car is lowering. If we were to put scales underneath the wheels during such an event, we would see that the load on the right wheel is decreasing, and the load on the left is increasing. Drag racers know this quite well, and try to combat the phenomenon by installing an adjustable air spring to apply a preload force to the lighter loaded tire on the right side of the vehicle.
 

rekabs

TWERK
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#13
Physics lesson.....from the WEB:

During hard acceleration, there is also a weight transfer from side to side across the axle based on the prop shaft direction of rotation and torque reaction. We refer to this as tire jacking. Since our reference point is the ground and the wheels are attached to the ground, it may seem difficult to see what is happening. It is actually quite easy to see what is occurring, but the explanation seems backward. We see the right side of the vehicle squat down during hard acceleration. The right wheel is being pushed upward toward the vehicle body. However, since the wheels do not leave the ground and the ground is our frame of reference, it appears that the right corner of the car is lowering. If we were to put scales underneath the wheels during such an event, we would see that the load on the right wheel is decreasing, and the load on the left is increasing. Drag racers know this quite well, and try to combat the phenomenon by installing an adjustable air spring to apply a preload force to the lighter loaded tire on the right side of the vehicle.
Interesting, feels strange. I think it has to be something more. Even my passenger noticed it.
 

phil mead

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#15
Closely inspect axle. BMW half shafts may be fatigued from the torque of the V8. It would take a very small amount of twist to cause your issue. ?????????????? good luck
 

Scott Harrison

"Growing old is mandatory, growing up is optional"
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#16
Closely inspect axle. BMW half shafts may be fatigued from the torque of the V8. It would take a very small amount of twist to cause your issue. ?????????????? good luck
Wouldn't you suspect the tires would break loose long before it twists a half shaft?
 

phil mead

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#19
I have heard about half shaft twist on the track with drag radials. Just noticed he said he was "not accelerating that hard" So probably not half shaft. Scott is correct about a sloppy CV joint. (easier to check also) In a BMW you would hear the bad CV joint. You may not in a Cobra. How hard of a pull is it? Is this new or has it always done it?
 

rekabs

TWERK
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#20
I have heard about half shaft twist on the track with drag radials. Just noticed he said he was "not accelerating that hard" So probably not half shaft. Scott is correct about a sloppy CV joint. (easier to check also) In a BMW you would hear the bad CV joint. You may not in a Cobra. How hard of a pull is it? Is this new or has it always done it?
It's more of a drifting sensation as I accelerate, not a hard pull. haven't noticed it before
 
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