U sure its not the driveshaft?

 

I suppose you know that drive shafts have to be balanced.

 

Had the driveshaft balanced by a local drag strip parts place that specializes in driveshafts. Please keep in mind that the driveshaft is spinning at 3 times the "frequency" that I am feeling this vibration at.

 

yea, the drive shaft was the only thing i could think of, but i remember him saying it was balanced. If it shaking as hard as he says, in neutral, i wouldn't suspect the drive shaft, but IT STILL COULD BE IT! I would have it checked by another shop.

 

Did you replace your rear axle shafts when you rebuilt the rear end or reuse the originals? I tracked vibrations in my truck and car to bent wheels but you can use the same method to check for a bent axle shaft.

I took a jack stand and taped a screwdriver to it horizontal to the ground. I then moved the jack stand with the screwdriver to the wheel lip until the tip of the screwdriver was almost touching. I then spun the tire by hand with the wheel raised of the ground slightly. There was a slight but noticeable change in gap as I spun the tire.

I'd do this on all 4 wheels and see what happens.

I suppose a balance problem with the axle shafts could also cause this.

It could still be a tranny vibration since even in neutral, the driveshaft is still spinning along with gears on the output side of the tranny. Can you feel the vibration in the shifter?

If your steering wheel is not shaking back and forth even a tiny but, It' probably not the front end.

How are your rear shock absorbers? Does the vibration occur on all road types? The spacing of the joints on highways has been known to cause the rearends of cars and trucks to bounce up and down in a frequency that causes a severe shake.

This is what I've found while troubleshooting my shaking problems so I hope this helps.

 

Great suggestions, and I've done them all. Being an engineer, I've actually used machinest dial indicators and checked "runout" at the lip of the wheel rim. It's OK.

In desperation I jacked up each front wheel AGAIN (for the 1000th time...) and this time I got rough with the wheel. Passenger side was tight as usual. Moved to the Driver's side and DAMN if I didn't hear a clunk! Drove down to my friendly tire dealer (just bought those rims/tires, so I knew I could get a favor) put it up on the lift, had the guys watch underneath as I forced the tire, and sure enough the upper control arm bushing is shot and the control arm can move in/out maybe a 1/2 inch or more!! I've ordered the new shaft/bushing kit and I'll have THEM install it when it gets here (I hate working with the Spring... had a bad experience when rebuilding the car!) Will also get the shocks replaced (lifetime warrantee...)

Think this would cause the kind of vibration I was feeling?? Or is this just something else that needs fixing that won't fix the vibration?

 

Great suggestions, and I've done them all. Being an engineer, I've actually used machinest dial indicators and checked "runout" at the lip of the rear wheel rims. Axles are OK.

In desperation I jacked up each front wheel AGAIN (for the 1000th time...) and this time I got rough with the wheel. Passenger side was tight as usual. Moved to the Driver's side and DAMN if I didn't hear a clunk! Drove down to my friendly tire dealer (just bought those rims/tires, so I knew I could get a favor) put it up on the lift, had the guys watch underneath as I forced the tire, and sure enough the upper control arm bushing is shot and the control arm can move in/out maybe a 1/2 inch or more!! I've ordered the new shaft/bushing kit and I'll have THEM install it when it gets here (I hate working with the Spring... had a bad experience when rebuilding the car!) Will also get the shocks replaced (lifetime warrantee...)

Think this would cause the kind of vibration I was feeling?? Or is this just something else that needs fixing that won't fix the vibration?

 

I really hope that's what the problem is. I don't know anything else to check. You could have someone drive along side you and see if they see any of the tires shaking if you haven't already done so.

Coincidentally, I just recently noticed another shake on my truck lastnight at 70MPH. I haven't driven it on the highway in a long time so I had no idea I had another problem. The shake was so bad I couldn't make out the cars behind me in the mirrors.

I jacked it up, and gave the front passenger tire a tug and sure enough it has about 1/4" of freeplay in the hub assembly. Unfortunately you can't just replace the bearings and races but instead have to replace the whole hub assembly! The dealer price is crazy so I searched every AutoZone within 100 miles and found 1 in the area for $227.

I installed it this morning and sure enough, no more shake.

so I guess it's possible that your shake is caused by the freeplay in the front end.

If your rear end bounces a lot when you push down on it hard, dead shocks could be contributing to the effect.

 

try jacking the car upin center of rear axle, then place jackstands under the ends of the axle as far out as possible, get it high enough for the tires to clear and chock both front wheels well. Run it up to speed while someone watches the rear wheels, then kick in in neutral at the speed you feel the vibration. If you find no vibration then you know its in the front wheels. If you hit the vibration then you know its in the rear. This will at least let you know whick end to work on, and you may be able to isolate the problem since it will be vibrating while the car is stationary.

 

upper control arm bushings helped the steering stability a lot, but it DIDN'T FIX THE VIBRATION PROBLEM!! I've ordered new outer axle bearings, since it is the ONLY rotating part left that I haven't changed, balanced or replaced!! Will keep this list posted...