[78 GHOST]

I don't think cutting is the answer as you've got the female nut imbedded in the mount and cutting would garf that all the heck.

Personally, I'd rotate the driveshaft 180 Degrees, drive and evaluate. Then think about swapping out the mount. I think I have my old one which is servicable if you're near Houston.

I had nagging vibration issues, was assured by 3 shops my engine and tranny mounts were fine, only to find during the frame off, the LH engine mount was wasted. No vibration now, it was nagging as I could never pin it to either the engine or chassis, wasted a lot of money chasing my tail on that one.

[SS-TA]

You can't cut down the rubber mounts as 78 Ghost has stated. Certaintly rotating the drive shaft 180 degrees is simple. As far as the Trans mounts if you have the ES its probably to tall. The mount heights I quoted you were for mounts manufactured for a 1972 Olds Cutlass with a 350 with T-350 trans, the application for a Pontiac with a different Trans maybe different. There is only one ES for all GM applications. The heights of the rubber mounts may have changed since I purchased these in 2005. The good thing is all these mounts are cheap. (I believe they are all mfg. in either Korea or India). Check drivline angles and the actual height of your mount if it isn't a ES. If it is about 1.80 inches than changing to another rubber mount probably won't help. Hang in there it was a while before I could drive my car because of the vibration.

[gtofreek]

I had two different GTO buddies that were running Ralley II wheels. Same issue. One guys, the vibration was so bad it trashed his tranny and main engine bearings. Turned out to be the Ralley II were worn out on the taper that the lug nuts tightened into. The lug nuts were actually bottoming outy on the brake drum before tightening up against the wheels. New wheels fixed both cars.

[tulsarockbreaker1]

I don't have a fraction of the knowledge of the previous repliers but I did have the following happen in my 1968 GTO, don't know if it could help you or not.

About 500 miles on rebuilt 400 with non-clutch fan. When I bought the car there was a clutch fan in the trunk so I thought I would try it. It vibrated starting probably at about 30 mph & got worse the faster I went. I put the old fan back on & no vibration.

Just a thought. Good luck.

[getmygoat]

Hi all,

Well, I finally had some time this weekend to fuss with the vibration issue.

First, I swapped the driveshaft around.

I put a floor jack under the pumpkin and jacked the rear wheels off the ground. Ran the car up to 80 MPH with the tires and drums off the car.

Smooth as glass.

Then added the drums (with lug nuts).

A little bit of vibration.

Then added the tires... Yeah, some more vibration, not terrible, but there... Seems different than when driving.

Took the car for a drive. Same old BS vibration.

Then I swapped the rear tires from my convertible (which is pretty smooth) to the hardtop (which has the vibration problem).

This seemed to make a significant difference. The car is much smoother now. Not perfect (the front tires are still the same, and the convertible tires (on the rear) have never been balanced since I've owned it, so they probably need a little).

So, the tires on the hardtop (first set) have been balanced several times.. so it might either be a tire defect that balancing doesn't pick up, or a rim problem of some kind? I did notice the holes for the lug nuts look a little "worn", almost egged out a very small amount. Should have got a pic.

So the question is - Now what? Do I buy a new set of wheels and tires for the hardtop ($$$$$$).

[getmygoat]

So today I swapped the front tires from the convertible to the hardtop. The convertible was pretty smooth at speed with its original tires.

The hardtop with only the convertible rear tires installed ran pretty good, still some vibration but much better.

Now with the hardtop running all four convertible tires, the thing shakes like crazy. Weird. Its way worse than the convertible is at that speed with the same set of times.

So, one theory is that the "on car balance" of the original hardtop tires compensated for an imbalanced front rotor? Now with the converitble tires on the front, there is no compensation so the rotor is showing itself... (Grasping at straws here).

[lust4speed]

Couldn't the tire be egg shaped but in balance? I picked up a nasty vibration on the way home on the freeway and about 2 minutes later the tire blew. The vibration in my case was the tire ballooning out in a weak spot just before letting go all together.

[gtofreek]

With the lug nuts tight and the tire jacked off the ground, have someone hold the brake and grab the tire and try to rotate it back and forth as hard as you can to see if it is tight or if the lug nuts are tightening against the brake drum.

[getmygoat]

Some reading I did on the internet indicates that road force balancing can make a big difference. Specifically, they recommended the following machine.

http://gsp9700.com/

Seems worth a try. Has anyone had experience with this, and where it made the difference?

[getmygoat]

Well, what I did was replace the two front rotors. I think the right one had been warped a while back by a frozen caliper I had right after the major restoration. Replacing that one helped significantly. Then I just replaced the left one, and again some significant improvement. I also replaced the back drums.. This eliminated some pulsation I had in braking, but didn't seem to smooth it out any more.

So - the car is now very enjoyable to drive!... I can't tell most of the time whether the car is vibrating or its just the road.. (San Diego highway - lots of concrete, grooves, etc).

And, I've got great brakes alll around that operate smoothly and stop well.

I think I slayed this vibration dragon!

Thanks for all the help you guys provided!

[Grant Miller]

That is great news!! I'm glad that you are getting to enjoy your car!