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Suspension - Brakes - Tires OEM to all out Performance - Brakes, Suspension, Wheels & Tires

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Old 08-06-12, 01:39AM   #1
T/A 1975
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Default Vibaration / shake @ 100+??

Hi Guys,

I have a perplexing vibration / shake issue with my T/A @ after 100mph. It feels like the wheels / tires, but I am starting to give up. I balanced the tires, replaced my old drive shaft with a new balanced one, new HD u joints, new motor mounts, new trans mounts, new ball joints, new tie-rods, new poly bushings etc etc.. Everything looks a-OK from my vantage point and my fellow gear head friends.. at a loss here. Shake seems to be coming from the front of the car...

There are no signs of vibration or shake below 100mph. My fellow gear-heads tell me to relax it's a muscle car etc... but I literally am afraid to push the car past that speed. With the 3:73's and a three speed tranny there aren't to many mph's past 100, but to me it just ain't right.

Hopefully some one has run into this before?

Thanks guys,
Trevor
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Old 08-06-12, 01:51AM   #2
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Did you check if the tires are separating. You should be able to see if you spin them and see high and low spots or a wobble
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Old 08-06-12, 01:33PM   #3
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Tire separation? Well, they are about two year old BFG's... I guess anything is possible... I am not balancing them with standard wheel weights I am using the stick on wheel weights because of the restored rims etc.. Could that be a factor?
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Old 08-06-12, 08:47PM   #4
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The balance does not matter.
If the tires are not round they are not round even if perfectly balanced.
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Old 08-06-12, 08:57PM   #5
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From what changes you've made I'd have to say tires. The could be cupped also. Which is hard to spot.
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Old 08-07-12, 07:14PM   #6
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Default Highspeed Vibrations

The age of the tires is the date they were manufactured, not when they were purchased and mounted on the rims. They could have been on the shelf up to "years" previous before sale. Even tires have a shelf life.

If the car sits for long periods of time raise it up on jack stands so the tires are just off the ground. Make sure they stay inflated.
Another thing to note. Using "air" to inflate tires is OK as long as it is a clean ,dry source of air.
High dew point "Wet Air" (that is air that contains a lot of moisture) when compressed will have that same amount of moisture concentrated in it when used.
If the moisture is not removed from the air before it goes into the tires it will fall out of suspension when the tires cool and "puddle" on the low side of the tire.If it freezes over night there will be ice formed inside the tire on the low side.That will cause an imbalance untill the ice melts.
That is one of the reasons nitrogen fills on tires are preferred. Nitrogen is cleaner , dry (no oil or moisture content) and expands /contracts less than "air".
Believe it or not : wheel trim rings added on after rim/wheel balancing (if not zero balanced themselves) can throw the balance off and cause vibrations to show up at certain speeds.
Avoid using "custom car show " doo dads like dice etc. etc.
for valve stem caps . Those add extra weight to the valve stem .If they were not compensated for when the wheels and tires were initially balanced ?
You guessed it ! OUT OF BALANCE!
Insufficient shock absorber cooling , damping rate or aged shocks can contribute to a high speed vibration.




If the tires have not been flat spotted during a panic stop this is what needs to be done to solve high speed vibration problems.

For sustained highspeed running tires need to be checked for roundness.
If they are mildly out of round they can be 'trued" on a machine that will remove rubber from the highside.


With the tires removed each rim needs to be checked separately for trueness/out of round , lateral runout and zero balance.
Used rims definitely need to be checked before mounting tires on them.
Even "new" sets of rims should be checked this way before ever mounting tires on them.

Each brake drum/rotor needs to be checked for out of round , zero balance and lateral runout.

Rear axel flanges need to be checed for out of round & lateral runout.
Are the axles straight?
Front spindle flanges need to be checked for out of round and lateral runout
Front wheel bearings need to be checked for proper preload & wear.

The drive shaft and U-joints can cause vibration problems.
A worn or improperly installed /binding u-joint can set up a vibration at speed.
Are the driveline angles correct?
Pinion and trans angles may need to be adjusted.

If the original stock driveshaft is still being used get the shaft checked for straightness .If it is a keeper get it highspeed balanced, if not, get a new one made.If a new one gets made use a larger dia. like 3".It will have less tendency to bend or twist.
The original drive shafts from the factory, beginning some time in the mid 1970's, had vibration issues because the factory saved money by not precision balancing them.
GM figured that since the national speed limit was 55 mph most cars would rarely see over that speed .Right around the same time the 80 & 100 MPH speedometers started showing up along with the unleaded fuel only gas gauges.

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Old 08-09-12, 03:16PM   #7
T/A 1975
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Hi Guys,

I believe you guys are correct regarding the tires. There are more then one issue due to age and sitting for some time etc..

I will have them checked with a hunter road force machine and this will reveal all!! I simply spun balanced them @ a friends shop a few times (good ol' snap on machine) and thought "I can rule out tires now". Silly rabbit...

Anyway, considering all other things are new / fresh/ balanced with my suspension and drive-train, I believe you gents are right in pointing me back to the tires.

I'll let you know how I make out after I find someone who has a road force machine... lol

Trevor
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Old 08-16-12, 02:21PM   #8
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When I had my '77 T/A, I had a vibration above 75 mph. I had my tires balanced, driveshaft balanced, changed rims, and still had the vibration. Eventually, I needed new brake pads on the front. I decided to get new rotors rather than turn the old ones. The vibration was gone. 0 to 140 mph. Obviously, the rotors were out of balance. I hope you find your problem quicker than I did. I went about a year and a half before finding my problem.
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