My friend has the above Mustang 428 C6 auto trans. He's getting a vibration between 3000 and 4000 RPMs. This winter he have the motor out, put a new cam in it so he could run pump gas and balanced and blue printed it. Balanced the driveline and put a new bearing in the output shaft of the transmission.
After all this work it still has the vibration. It has a 9 inch rear end with the Detroit locker. My thoughts are that the problem is in the rear end what are your thoughts?
Oh and I forgot to mention the vibration is worse in third-year then second gear, so somewhat speed related but still between 3000 and 4000 RPMs.

 

Could be a pinion bearing... Sure it's not just a tire vibration?

 

What kinda shape is the harmonic balancer in? Freakin sexy car too by the way.

 

I vote torque converter.

 

I'd check simple things first like have the tires balanced and maybe flywheel/harmonic balancer

 

We went all over a chevy once, and found the exaust hitting the body was causing it to vibrate.

 

I would assume you balanced the trans and torque converter with the driveline. If not then that may be the problem. But try rotating wheels and checking tread. Easiest solution and if its been sitting it may have flat spots, delamination or even water in the wheels. Then put it on jackstands and let it idle in gear. Listen for noise and watch for wobble. Sometimes a strobe or timing light helps.

 

Thanks for the ideas! I forgot to mention car has little over 400 hp at wheels and over 500 ft/lbs torque, runs low 12's. I should have taken some pic's of the motor ect... The rims and tires are new this year, hes gone thru almost everything trying to find that vibration. I'll have to ask him about the torque convertor. I still think he's putting so much power to the wheels it's something in the rearend. I think he should put a 8.8 in it, I know this is debatetable but the 8.8 is a stronger rear vs the 9 inch.

 

X2

 

what kind of vibration we talking? like really light or your getting thrown around a little?