vibration felt in drive shaft at track

[frankym]

Ok,

Having trouble diagnosing a problem. I took my superformance to pocono last saturday at the north course. I began noticing that particularly out of tight turns on full acceleration, the car felt a little loose, like the drive shaft was vibrating or picking up vibrations from the rear end.

After a run, we jacked the rear of the car off the ground and with one man holding the alternating wheel, we rotated the opposite rear wheel front to back to determine if there was excess play in the CV joints. There appeared to be slightly more play in the passenger side rear wheel than the driver side rear wheel. We also shook the wheels at various angles while on the lift to see if there was play in the wheel bearing but it was tight. The excess travel was about 3-4 inches in outside tire circumference, and maybe 2.5-3 inches on the driver side rear, not sure if these are tolerable amounts of play.

I am not sure what could be casusing this feeling of excess play in the rear. Simultaneous to this, the car also feels a little notchy (but sporadically) when disengaging the clutch in reverse, like clutch chatter / uneven surface on flywheel.


The notchyness in reverse occured on another cobra I had with a live axle and after replacing the axle seals and putting in new differential fluid, reverse became smooth. I brought my SPF to my SPF dealer and when I took the car out for a ride with the mechanic, the car ran exceptionally well, but maybe the car needed to be driven hard for a while before the problem persists. On the track the sound and vibration out of turns was constant, and on the street, it's sporadic. Not sure what it could be but the mechanic said after doing a visual inspection of the chasis on a lift, nothing jumped out at him, not sure if he removed the axle boots or inspected the differential but I wanted to see if there are others out there that have experienced this.

I am also trying to rid the carburetor of a hesitation in performance around 2k rpm. I am going with a Barry Grant demon 750 with mechanical secondaries, my current holly has no metering block for the secondaries. so it might be harder to get the existing carb tuned right, plus, it's a stroker motor so it might benefit from a racing grade carb.

appreciate any help.