# bad vibrations



## mbspeed (Sep 25, 2012)

HI all got a 67 GTO with bad vibrations when I drive over 60 mph..
car sounds like its going shake apart its a 4 speed and I think problem is in the drive line ,,,,,I tried every thing could think of stop the vibs I have change pinion angles balance rims new drive shaft... also the car has massive wheel hop if you spin tires off the line ...and car ripped a few motor mounts stock and mighty mounts I am guessing from the wheel hop ..new center force clutch car is nice and smooth up too 60 mph and I keep pushing the car when I make a correction but still feels the same any ideas will be helpful thanks :banghead::banghead::banghead:


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## PontiacJim (Dec 29, 2012)

Sounds like you have done some checks that I would already tell you to do. But....

1. Make sure your universals are centered (front and back) and see that none of the "C-clips that secure them are missing. Is your driveshaft centered - side to side, and not at any angle coming from the trans to the rear axle?

2. Make sure the rear universals is centered on the rear axle front pinion. There are 2 cast in tangs, one on each side, that your u-joint cap is held in by. The caps have to be seated between these tangs before you install the U-bolts and tighten them down. If one of the caps is caught on top of the tang, the cap will not be fully seated even though you tightened the U-bolts.

3. It is possible that you have a tire/tires out of round (flat spot) *OR* a tire which has had the radial belt inside it slip/break. I just had one break on my '97 Toyota and the tire was not very old and the tread was very good. I took a good hard look at it and in the center of the tread, running around the tire, there was a pronounce "valley". Never saw anything like this before, but I have had radial tire belts break/shift on some other tires and it does indeed produce a very bad vibration over a certain speed. 

4. Bad shocks in combination with a bad tire - your tire may be bouncing like a basket ball as it goes down the road.

5. Have someone drive alongside you at the higher speeds you get the vibration and check both sides of your car for any unusual signs of a bad/bouncing tire (front or rear). Wheel-hop can be very violent and punishing on the tires, suspension, and drive train and must be eliminated or you will do some real damage.

6. My brother had a vibration with his '73 Plymouth, my fault. Some how I put the transmission mount in backwards (looked OK to me while on my back!) and when it was switched, it cured most all of the vibration. You may want to check the angle of your driveshaft coming out of your transmission to make sure it is not pointing upward towards the floor. Does your car sit level like factory or is it raised up in the rear?

7. On bigger HP with a lot of engine torque, you may want to "chain" the engine to limit the amount of twist the engine mounts have. I have never done this personally, but have seen a few who have -whether or not it works. Solid mounts in my opinion are not good for a street car.

8. You have to address the wheel hop. You can install a set of "no-hop" bars which bolt on the rear end and raise the upper control arms to change the suspension geometry. They are designed to stop/help wheel hop. ALKY extended his lower control arms down to do the same thing. Check out the thread "PMT Rear Control Arms" for a better explanation and photos ALKY posted.


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## BearGFR (Aug 25, 2008)

All good advice from "PJ". Also possible that your wheel hop problems and vibration problems have the same cause. If your rear control arm bushings are too worn, that can cause the wheel hop (too much play) and also vibrations (driveline angles off due to axle housing rotation). If the centerline of your crank/transmission and the centerline of the pinion in your rear axle aren't parallel with each other, it'll cause vibration.

Bear


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## mbspeed (Sep 25, 2012)

thanks Pontiac jim and bear...my upper control arms are new and adjustable lowers are also new boxed style.... all bushing to diff are new as well my you joints are new and centered good ...my trsns tail is up about 3 degrees up.. with a poly mount with out the extra mounting plate.. my rims and tires new and I rechecked ..when I am driving 75 on freeway can feel the vibes most from shifter I have cargo coils with air bags and air shocks I was going try new rear drums because I think break pedal does not return to correct rest position its like it gets stuck about 1" down some times and I need pull it up by hand when I stop or break light stay on.... I figured a different problem do guys think if I fit wheel hop high speed vibs will go away this sucks ..think my next step is to have my girl follow me and report on problem like you guys said .,:: or maybe set up the gopro camera under car having so meany problems trying get car 100%:nopity::nopity::mad2::mad2:


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## BearGFR (Aug 25, 2008)

Considering the changes you've made, I'd definitely start with making sure your angles are right. Here's a really good explanation. 


http://www.hotrodhotline.com/md/html/drive_shaft_harmonics.php

Bear


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## PontiacJim (Dec 29, 2012)

BearGFR said:


> Considering the changes you've made, I'd definitely start with making sure your angles are right. Here's a really good explanation.
> 
> 
> Drive Shaft Harmonics
> ...



Good article to read from Bear. Read the last 2 paragraphs as this may apply to your problem. I don't like that your transmission is 3 degrees up, and that articles states it should be no more than 1 degree from level. I would definitely try to get that trans level. Use your frame to get your overall car back to level and then check your trans at the output shaft and adjust it to be level with the frame. 

Then I would drop the car to the ground and get the cars weight on the suspension (you may want to do this with a full tank of gas for more weight) and then check the pinion angle now that you have the transmission where you want it. Since you leveled the trans to the frame and your car may be higher in the rear, this won't matter because now you are measuring the pinion angle at the rear end, and not levelness.:thumbsup:


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