Vibration through car at speed

[andy625]

I have an '87 Firebird 5.0 and I have a problem with vibration through the car (not the steering wheel) at 60mph+.

I was originally told that this was due to 2 of my wheels being buckled, so I bought a set of 2nd hand Transam wheels & tyres (these are slightly wider than the original set).

I had the new wheels fitted & balanced (they look awesome!), but was told that one if the tyres had a sght "flat spot" presumably where it had been stood around whilst fitted to the previous car. This tyre is fitted to one of the front wheels.

Now, when I am on the motorway (I live in the UK), I still get a vibration when travelling 60mph or faster. I've had it up to 85, and the vibration is still there, doesn't seem to get any worse or better, just different frequency.

can anyone tell me whether this is likely to be the tyres, or is it more likely to be the propshaft, or a halfshaft that are bent or out of balance, seeing as how I've had the wheels balanced? I can't really afford to buy a new set of tyres just to see what difference it makes - I got into enough trouble for buying the wheels!

Any advice would be appreciated as this is spoiling an otherwise good car.

Andy

[volkerc]

Originally Posted by andy625

I have an '87 Firebird 5.0 and I have a problem with vibration through the car (not the steering wheel) at 60mph+.

I was originally told that this was due to 2 of my wheels being buckled, so I bought a set of 2nd hand Transam wheels & tyres (these are slightly wider than the original set).

I had the new wheels fitted & balanced (they look awesome!), but was told that one if the tyres had a sght "flat spot" presumably where it had been stood around whilst fitted to the previous car. This tyre is fitted to one of the front wheels.

Now, when I am on the motorway (I live in the UK), I still get a vibration when travelling 60mph or faster. I've had it up to 85, and the vibration is still there, doesn't seem to get any worse or better, just different frequency.

can anyone tell me whether this is likely to be the tyres, or is it more likely to be the propshaft, or a halfshaft that are bent or out of balance, seeing as how I've had the wheels balanced? I can't really afford to buy a new set of tyres just to see what difference it makes - I got into enough trouble for buying the wheels!

Any advice would be appreciated as this is spoiling an otherwise good car.

Andy

the flat spot is most likely causing it. take off the wheel/tire in question, put on your spare and see if you still have the vibration.

[tri-power]

There is a possobility that you might have a wheel balance issue. You might have a heavy spot where the rim and wheel have all the weight in one area. Try to have them re balanced. If the balancing place has spin balancers, you should be able to see if the tire is out of round when it is turning. A hanging brake caliper could also cause a vibration, however that you should normally feel in the steering wheel. In the north east the flex hoses have been known to go bad from the inside out causing the caliper to hang up. the chances of the drive shaft being out of balance is slim but not impossible. If the universals have been changed and not balanced, there is a small possibility. Check to see that the universal joints are not sticking.

[andy625]

I had a mechanic check all joints and bushes, and he thought they were all ok. He did say that there was a slight amount of play in one of the prob u/j's but nothing that would cause a problem.

The tire with the flat spot is on the front, so I would have expected it to shake the wheel rather than through the car.

I may try getting them re-balanced. Have to gamble with £23 ($40), cheaper than new tyres though!

[Philo]

Originally Posted by tri-power

There is a possobility that you might have a wheel balance issue. You might have a heavy spot where the rim and wheel have all the weight in one area. Try to have them re balanced. If the balancing place has spin balancers, you should be able to see if the tire is out of round when it is turning. A hanging brake caliper could also cause a vibration, however that you should normally feel in the steering wheel. In the north east the flex hoses have been known to go bad from the inside out causing the caliper to hang up. the chances of the drive shaft being out of balance is slim but not impossible. If the universals have been changed and not balanced, there is a small possibility. Check to see that the universal joints are not sticking.

There are two types of flatspots - the kind caused by the tire sitting in one position for a while, and the kind caused by a skid where rubber is worn away when the tire is not turning but the car is moving. The first kind generally goes away when the tire is used for a while, but the second will not go away - and the tire can be perfectly balanced. Remember, a balanced tire does not have to be perfectly round. A good example of the last type of flat spot is with an airplane. When they land, the tire is not moving, but must accelerate to the speed of the airplane in about one second (see the smoke?) leaving a flat spot on the tire. When I was in the service, I changed many fighter plane tires that flat spotted after only one landing. In fact, some fighters had lockouts on the brakes until after the touchdown so pilots could not hold the brakes on during touchdown - which causes instant blowouts.

[89camaroperson]

Could be your driveshaft is out of balance or worn u-joint bearings. I think that is what the cause of the vibration is on my 89 camaro with a 5.0 in it. It feels like the shaking is in the seat or down low when your driving instead of a tire. Just a possibility. Get an aluminum drive shaft off of a formula or z/28. Might help.

[Twizted_3KGT]

If it was the driveshaft you could rev the engine up while sitting still and it would vibrate the car. This is only at higher speeds so i'd say your tires are to blame. One or more could be out-of-balance, out-of-round, or have damaged tread. Even with a completely balance wheel, if one of these other problems exists you will get a vibration similar to that of an unbalanced wheel. Look to your rims and tires for the problem, bent rims and abnormally worn tires are common and often to blame for vibrations at higher speeds. I wouldn't think it would be suspension related.