Drivetrain Vibrations
 

I have a 1965 gto with an LS 2 with T-56 6 speed, moser 9" ford rear with 389 gears. I have baer brakes (track style) metco aluminum control arms (upper adjustable). I have a vibration around 65- 70 miles per hr. on up, never goes away. I have adjusted my pinion angle from +3 to -3. (The angles are set now at engine down 3.5 and rear pinion up 3). I keep going through rear axels bearings where the rear end grease penetrates the bearing. To stop the vibrations I have replaced the the axels, tires, rims, bearings, driveshaft, universals, center section, and housing. The t-56 tail shaft bushing is tight and there is no seal leak (8500 miles) No broken motor mounts. The frame of the car is straight (within manufactures specs).

NOW WHAT? I do not know what to do. thanks, steve fenimore

i know ist a dumb post... but are you sure its the rear tires or driveline that shakes?? i mean the front wheels are running the same speed..

does it shake on a lift/dyno?
have you replaced both axles?
is the centersection in ballance? .. (does it shake on the lift with the axles pulled/removed?)
is the driveshaft ballanced with or without the yokes that are on the car?
are the flanged squared.. front and rear?

Does the vibration go away if you drop a gear?

The car has four new rims and tires, the complete rear has been replaced moser 9" new from moser (2nd one). The drive shaft is in phase, new aluminum one balanced with yoke. I saw it balanced. This is a drive line vibration you cannot mistake it. The thing is I was thinking it was the clutch or maybe the pressure plate, but whipe out rear axel bearings? and when you push in the clutch it does not go away when the motor is idling and your rolling over 70mph.

If it was a Clutch issue it would happen at the same RPM everytime. Since it is MPH even in Neutral it has to a drivetrain issue. It sounds like it is an issue in the drive shaft or rear axle.
I doubt it is pinon angle if it does not go away at 70 in neutral.

Did you check that the wheel weights are still on the rear tires and wheels?

Rodger

had the same problem
 

on a friends car. He went from a GM 12 bolt to a 9 inch ford. The Gm is hub centric and the ford is lug centric. Meaning the wheel fits on the raised portion of the axle to center the wheel on a GM. On a Ford, the style of lugs center the wheel. What happened was the same wheel and lugs were used when he switched to the 9. The wheel would move and get off center causing a vibration at high speeds....basically wheel run out.

You can either change lug style and make sure the wheels is sitting flush on the axle pad or machine a thin spacer with a hubcentric centering ring.

Does this make sense?

Good call Payton, a chassis dyno session would go a long way there. I'd also look for a bent axle tube. Measuring your wheel runout on the car would be a good starting point.

vibs
 

I have new foose wheels with centering rings and I have spun the drivetrain up to 80 mph and could not detect much vibration or its location. The wheel runout is not significant and the vibration is definitely not wheel related. axels are not bent.

I appreciate any and all help, comments, what ever suggestions, thanks, steve. keep them comming, maybe there will be something I have not done.

Another thought. With an engine swap, the centerline of the crankshaft and the centerline of the pinion need to be parallel, both vertically (which you have experimented with by changing pinion angle) and laterally. They do not have to be perfectly in line with each other, just parallel. Some early big block cars had the front of the motor shifted to the right (passenger side) to give more clearance for the exhaust/steering on the left -- making the crank centerline non-parallel laterally with the pinion. I have seen driveshafts for those cars with the u-joint yokes factory-welded slightly out of phase (10-15 degress, as I recall) to minimize vibration -- definitely a crutch. You have probably already checked, but I would make sure things are parallel in both planes. Good luck.

Pappy

vibs
 

A ford nine inch rear pinion is not in the center of the car, but the pinion and tail shaft are parallel. This creates an angle as well of one or two degrees I believe. Are you saying to make the yoke and pinion out of phase to correct this. thanks steve