I need your help, badly!

68stang351

Founding Member
May 16, 2002
850
9
39
Savoy TX
Ok, for about 4 years now I've had this annoying shake. I'm hoping someone can help me because I'm really getting tired of it. I will present you the facts.

It only happens between about 65-85 mph, and only when I'm coasting or maintaining a steady speed. If I'm on the throttle it doesn't do it.

It started happening after I replaced all of my front suspension and changed the rear end. I did all of it at the same time. (It was a 6 cyl., so I put a 8" in). I've ruled out the driveshaft, because I've used 4 different driveshafts in it and it still does it. I've even bought another trans crossmember and mount. I've had all wheels/tires balanced.


I should note that I've never had the front end aligned, however the car goes down the road straight. So I guess it could be coming from the front.
I'm not sure if its in the front or the rear, but I'm thinking it's the rear.
The whole car shakes horribly.

I think that maybe I have a pinion angle issue. I think this because that it only does it when I'm not on the throttle. From my thinking, the pinion angle is acceptable when the rear is slightly turned from applying the power, but when I let off the gas, and the rear is no longer applying power, that it settles back into a bad angle. Am I correct in this being a possibility?

I'm also questioning the engineering integrity of my traction bars. They are the kind that have the u bolt/shock mounting plate welded to the traction bar. It looks homemade. I'm wondering if that could cause the problem.

Should I have the pinion angle checked?
Should I have the front end aligned?
Or can you think of something else it might be?

I really need help with this, it's making the car no fun to drive.
I appreciate any advice.:SNSign:
 
It ain't the traction bars. My Lakewoods are built the same way. And they're not cheap pieces. Could be a pinion issue or the tailshaft bushing in the transmission tailhousing is worn out. Could also be bad tires, does the frequency of the vibration correlate to the driveshaft rotation or the wheel's rotation (wheel rotation is slower than the driveline)
 
It ain't the traction bars. My Lakewoods are built the same way. And they're not cheap pieces. Could be a pinion issue or the tailshaft bushing in the transmission tailhousing is worn out. Could also be bad tires, does the frequency of the vibration correlate to the driveshaft rotation or the wheel's rotation (wheel rotation is slower than the driveline)

"D", lets throw in "U" joints?

HistoricMustang
 
It's definitely not u joints. I've used many different sets with many different driveshafts.

The tires are M/T Drag Radials, only about 1.5 years old, it still shook before them, as well as when they were new.

does the frequency of the vibration correlate to the driveshaft rotation or the wheel's rotation

I just went and drove it and payed close attention to what it did.
It shakes at the same speed no matter what gear i'm in (3rd, 4th, 5th). So I guess that would be wheel rotation.

It doesn't shake at all if I'm in the throttle. But if I maintain speed, it shakes. If I coast w/ no throttle, it does it the worst.

Thanks!
 
I edited my last post, but not before you replied. You might not have seen the edited post. I went and drove it.

What I meant was the going a set m.p.h., it shakes at the same frequency no matter what gear I'm in.
Thanks. I think we'll get it figured out.
 
It's definitely not u joints. I've used many different sets with many different driveshafts.

u-joints dont have to be bad to cause a vibration. if they are installed incorrectly they can be slightly offset which will cause a vibration.

something else to check is the brake drums and rotors. if they are out of balance you get a vibration. this can be checked with the tires on the car. i forget the name of the machine used.

one last thing to check after you have looked at the above items. ok two last things;

1: look for a bent wheel
2: check to make sure the tires are round. i have seen tires out fo round enough that you could actually see it when the tire was spinning on the balance machine. tires can be trued by trimming the tread on a lathe.
3: check for a bent spindle(ok i lied again:D )
 
I have just been through this issue too. I found my pinion angle was the issue. My trans angled up 4 deg, and the pinion nose at 2 deg down. I replaced my rear first off after 4 years of dealing with the vibes, and it was still there afterwards. I bought some 4 deg shims for the spring perches, and it is now smooth. I couldnt believe it when I did it, because my other rear that was only 5 years old was good. It was all in the angles. You want the trans angle to be equal, or possibly 1-2 deg down from the trans, so when the pinion rotates up under load, they are equal.
 
Put it back on the jack stands. Remove the rear tires. Install a couple of lug nuts to hold the brake drums in place. Run the car up and see if the vibration is still there. Then remove the brake drums. After doing so DO NOT STEP ON THE BRAKES AT ALL. Run the car up and see if the vibration is still there. Let it coast down - DO NOT STEP ON THE BRAKES.

If the vibration is still there you almost certainly have a pinion angle problem.

Good luck. I have a vibration and I have done everything you have done and I have shimmed the the pinion up twice (4 degrees and then 6 degrees). Still have the vibration.
 
Put it back on the jack stands. Remove the rear tires. Install a couple of lug nuts to hold the brake drums in place. Run the car up and see if the vibration is still there. Then remove the brake drums. After doing so DO NOT STEP ON THE BRAKES AT ALL. Run the car up and see if the vibration is still there. Let it coast down - DO NOT STEP ON THE BRAKES.

If the vibration is still there you almost certainly have a pinion angle problem.

Good luck. I have a vibration and I have done everything you have done and I have shimmed the the pinion up twice (4 degrees and then 6 degrees). Still have the vibration.

Thanks, I will definetely try that.

As for axle bearings, I put new ones in before I put the rear in the car.

And thanks for everyone's help!:nice:
 
Okay, I tried 68RCode's suggestion. Even with the drums off it still shook. Not near as bad as when it was on the road though.

I could tell no difference in the shake with drums on vs. drums off.

Pinion angle? I have some 2 degree plates I guess I'll put on if I can ever find them. I bought them 4 years ago before we moved.
 
something else to check is the brake drums and rotors.




WOW! I feel stupid now!!!

I never looked at the drums. I decided to put my Bullitt wheels on yesterday and for some reason only just now noticed that one drum has a weight on it and one doesn't. I went and put a new pair of drums and I now have no vibration at all.

What an idiot!:doh: It only took me like 8 or 9 years to figure it out when it was something so simple, and someone even suggested it!