Rear end slight shift at acceleration

rekabs

rekabs

Steve Baker
Contributing Member
Member
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.
 
Every time I had the feeling, it was a half shaft about to go. Check your driver's side.
 
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:
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.
 
I've always found thats its my right foot that causes that problem
 
Rob Burton said:
No, For you, it is definitely the loose nut behind the wheel!!!
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Scott Harrison said:
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.
Click to expand...

Interesting, feels strange. I think it has to be something more. Even my passenger noticed it.
 
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
 
phil mead said:
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
Click to expand...

Wouldn't you suspect the tires would break loose long before it twists a half shaft?
 
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?
 
phil mead said:
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?
Click to expand...

It's more of a drifting sensation as I accelerate, not a hard pull. haven't noticed it before
 
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