My 1988 Chevy Cavalier Z-24 has developed a vibration. It’s fine up until I hit 67 and then it starts to shake, a little more the faster I go.* It doesn’t sound like a motor problem, but IANAM (obviously, or I wouldn’t need to post here).
I have new front tires (it’s a front-wheel drive) but I do need new rear tires… could it be something with the tires or the tire setup?
It seems to be worse when it’s cold out. When it started about 3 weeks ago it was a lot colder out and it would start vibrating at 63. It’s been warmer lately and it’s at 67. The other day it was cold again… back down to 64. Incredibly hot today, and it didn’t shake at all (of course, I didn’t go over 68). This could, of course, be coincidence.
Should I just get new rear tires (since I need 'em anyway) and hope, or does this sound like symptoms of something bigger that could cause painful and immediate death?
[sub][sup]* Not that I would know, of course. I wouldn’t go over the speed limit…[/sub][/sup]
Did you have the front end aligned when you replaced those front tires? I imagine the vibration could possibly be caused by bad back tires, too. - Jill
My first guess would be a tire seperation. Take a good look at them. Especially the front ones.
I did have the front end aligned when the new tires were put on. It needed it too (uneven wear & a bad pull). The front tires are wearing evenly and it doesn’t pull anymore, so there’s nothing radically wrong with the front-end alignment. Bad uneven treadwear on the rear, though. I’m going in for new rears in a week, and I’ll get an all-wheel alignment then.
I thought and hoped the vibration would be explained by the tires. I just wanted to make sure there isn’t some kind of evil immediate-death bunnies that live in cars and KILL, and have the same symptoms. 
And that would be where??? Legally.
Of course, I’m speaking from an academic point of view. ::rolleye::
I never said MPH did i?
For the record, it’s quite legal to drive 70 on plenty of highways in Texas.
As for the question, I dunno. But the title reminded me of one lovely trip from Houston to Austin with my girlfriend at the time. 
(my car started vibrating at 70).
Here in Alabama, and up through Tennessee, the speed limit is 70 on the Interstates.
That said, my truck, at one point, would start to vibrate at around 72. [sub]that’s not speeding. when i do 80, that’s speeding[/sub]
I had just gotten new front tires, plus a wheel alignment. The tires had been balanced.
I brought it back in, they checked, and it turns out I threw a weight, causing the tires to be out of balance. They replaced it, I was fine for a few days, then it started up again. Brought it back one more time, and the replacement weight was the wrong type, and it had slipped a bit. They put the right type on (the owner did the work this time), and the truck has been fine ever since.
In my case, I have aluminum wheels, which have a tendency to toss weights. So, I would have someone check the balance on your front wheels, especially if they are aluminum.
As for the differential in the shimmy speed vs. ambient air temperature, my guess is that it’s likely due to increased air pressure within the tire on a warmer day.
To follow up Dire Wolf, my #1 suspect upon reading your post was out of balance front wheels. One (not necessarily conclusive) test for that: if you can get up about 10-15 mph past when the shaking starts and it smoothes out again, check the balance. #2 suspect is worn tie-rod ends. A third possibility is out-of-round tires (I’ve experienced that - Dunlops - no cure besides replacing the tires).