COOLTED

The '79 has a vibration that only occurs at speeds arouind and over about 65 mph. It makes me think U-joint. The thing is... I have had the car checked over quite thoroughly about 8 months ago and all was fine. Is it possible for a u-joint to be bad and not show it during an inspection?

The car sat for quite a while before I got it. perhaps about 8 years. I realize that tires can flat-spot, but I would think I would feel that at all speeds.

Thanks for any thoughts.

sstopczy

My thought is if those tires haven't been changed after sitting 8 years they should be immediately. 7 -10 years is a rough life of the rubber. Most shops won't touch wheels and tires if they are older than 10 years unless they are replacing them.

toobroketoretire

A flat spot on a tire or a half shaft u-joint would give you about 775 times-a-minute vibration and a drive shaft u-joint would give you a 2000-2500 times-a-minute vibration. If a front tire was the cause you'd feel it in your steering wheel and if a drive shaft u-joint is causing it you could feel it in the center console.

As the half shaft u-joints are always under a compression load they're harder to check.

COOLTED

Yeah. New tires this spring. It's a shame, these still have valuable smoke in them.

It is definately resonating throughout the car, not in the steering wheel.

toobroketoretire

A failing u-joint would be the most likely cause of a high-frequency vibration because of the high rpm that the u-joints operate in. And I would suspect the drive shaft u-joints because they spin at 3+ times the rpm as the half shaft u-joints.

You can easily check the drive shaft u-joints by using two large Channel Lock types of pliers; one to hold the yoke and the other to twist the drive shaft. If you detect ANY movement that u-joint is shot.

stumpshot

I had a 55-65 mph vibration. Shop that did my alignment wanted to replace all the u joints. Took it in for a tire balance and that fixed the problem although none of the tires were that far out.
I don't think u joints fail all that often and you usually get a pretty good clunk when putting it in drive if they are going.

AboveTheLogic

The first thing that came to mine was tire balance. If you're considering replacing the tires anyhow, might as well do that and while its up in the air, check on the drivetrain health.

If the tires are still good, it isn't too expensive just to balance them again.

OMF

Another thing to check is the transmission mount.....if it's original it could be on it's way out and not be able to hold things stable at speed.

COOLTED

Thanks all, gonna start by checking the tranny mount. It's easier to change than u-joints.

JC68

COOLTED

If your tires are old you could also have a problem with the belts coming loose. If this is true you will only feel the vibration at certain speed ranges. When I first bought my 68 it would vibrate only between 50-55 mph on the 15 year old tires it had on it. Above or below that speed everything was fine. Replaced the tires and it went away. My suggestion is replace your tires first, and if that doesn't fix your problem then worry about the rest.

John

biackbenz

Hey CoolTed,

Does the amount of vibration change when you let off the throttle and coast? Have the same issue with my '78 and the vibration occurs at 60 + MPH and it is constant. Somewhere I think I heard that U joints will vibrate under load bur not while coasting. Curious how yours reacts. I think my issue is tires and im not sure how old they are.

AboveTheLogic

That's how it was for me years ago on my old z-car. Vibrated under load but not when coasting. Replaced the u-joint, all good after that.

COOLTED

The vibration is always there, power, cruise or coast.