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vibration about 75 mph?
- Thread starter 1stTurbo
- Start date
72firebird
Super Moderator
could be a lot of things, anything that rotates will hit a resonate frequency and when you hit a multiple of that frequency you're going to see an amplitude of the magnitude. So you're going to see a similar problem if it's a tire or drive shaft. If you haven't had the problem before I'm going to guess it's either a tire or alignment problem, driveshaft problems don't normally just pop up out of no where (not saying it never happens), but it'll normally be a tire problem especially if you just had something altered on alteast one of them.
Also since you're seeing an amplitude at certain frequencies that means that you're seeing the change in the amplitude at those frequencies so it's directly related to something that is changing, at those speeds I can almost guarantee it'll be a tire too, you'd see the driveshaft at lower speeds and all multiples of the speed.
Also since you're seeing an amplitude at certain frequencies that means that you're seeing the change in the amplitude at those frequencies so it's directly related to something that is changing, at those speeds I can almost guarantee it'll be a tire too, you'd see the driveshaft at lower speeds and all multiples of the speed.
Did you just put new tires on it? We have been having a lot of problems lately at our dealership with tire manufactors selling us new tires that are out of round. We had a brand new van that we ended up replacing 5 tires under warranty before it would roll smooth. I agree with checking the balance and while the tire is on the balancer look at the top of the tire as it is spinning and see if it has a hop to it.
If it is not a tire issue I don't know. I had a 96 Bonneville (a very different car from any sports car) that I bought with over 100,000 miles but drove it until 254,000 miles. It had a 70mph vibration all the while I owned the car. Just didn't drive 70mph. We replace the tires 3 times (not for the vibration just kept wearing out every 50,000 miles), we replaced the shocks/struts, we replaced the CV shafts thinking they were causing the vibration and got 4 or 5 alignments over the life of the car. We replaced all of the steering parts (tie rod ends, even the steering rack) and nothing fixed the vibration. I talked to the new owner of the car who is still driving it with 270,000 on it now. They mentioned that it has a slight vibration at 70mph...ugh. I guess the point of my story is that some times these little vibrations are hard to find. I sure hope it is a balance or tire issue for you. Good luck!
If it is not a tire issue I don't know. I had a 96 Bonneville (a very different car from any sports car) that I bought with over 100,000 miles but drove it until 254,000 miles. It had a 70mph vibration all the while I owned the car. Just didn't drive 70mph. We replace the tires 3 times (not for the vibration just kept wearing out every 50,000 miles), we replaced the shocks/struts, we replaced the CV shafts thinking they were causing the vibration and got 4 or 5 alignments over the life of the car. We replaced all of the steering parts (tie rod ends, even the steering rack) and nothing fixed the vibration. I talked to the new owner of the car who is still driving it with 270,000 on it now. They mentioned that it has a slight vibration at 70mph...ugh. I guess the point of my story is that some times these little vibrations are hard to find. I sure hope it is a balance or tire issue for you. Good luck!
WS6
Stay thirsty my friends
When I got the Can am restored and on the road I had a vibration like yours, so much so it would shake the empty passenger seat. First thing I did was to have the new BFG's rebalanced. It helped some but actually moved the point of vibration. Still not happy I changed all the shocks(which were new) to KYB gas. That helped allot, for awhile, and then it was back. Thinking that I had a bent steel wheel I had a set of aluminum snowflake wheels restored, which included an assurance of trueness. Put the new BFG's back on those wheels and had then 2 plane balanced on a different balancer. Vibration? still there:censor:. Over the next winter I put the 4 speed in and now the vibration was worse
. So I decided a simple solution it was not. So next I spent an obscene amount on a pinion angle gauge only find I was within specs, not to be deterred I changed the new U-joints out figureing I had messed up the installation. That time I had a driveline shop install them. All to no avail. They suggested an out of balance drive shaft. Hey! that's probably it! So it got balanced and it helped somewhat, almost to the point of living with it....but no, it started bugging me again so out came the driveshaft and back to the shop to have a brand new one made to a custom length and new U-joints again. This helped some other problems(driveline bind because it was 5/8" too long) I was having with clunking on gear change.
But after all of that the vibration was still there. I decided that I was being too fussy and that's how old cars were, and I just needed to live with it. After all, I was about to get new axle shafts because that was the last link in the chain of possible problems. And I was growing weary of putzin around with this problem, besides, it was just a car show cruiser. What's the big deal?
In the end it got fixed, not with axle shafts, but with what an old timer told me at the tire shop..."put a different set of tires on it"
He was right, those brand new BFGs with 1200 miles on them had one square one. I swapped them out for Goodyear eagles and the car was so freakin' smooth it scared me. I watched those get balanced like 3 times, no wobble, no excessive run out, just a poorly built one. And that fix cost me nothing because of a warranty.
All that work for something that I couldn't imagine from the begining. A bad "brand new" tire.
So, the moral? keep it simple and save your self some money.
...
. So I decided a simple solution it was not. So next I spent an obscene amount on a pinion angle gauge only find I was within specs, not to be deterred I changed the new U-joints out figureing I had messed up the installation. That time I had a driveline shop install them. All to no avail. They suggested an out of balance drive shaft. Hey! that's probably it! So it got balanced and it helped somewhat, almost to the point of living with it....but no, it started bugging me again so out came the driveshaft and back to the shop to have a brand new one made to a custom length and new U-joints again. This helped some other problems(driveline bind because it was 5/8" too long) I was having with clunking on gear change.But after all of that the vibration was still there. I decided that I was being too fussy and that's how old cars were, and I just needed to live with it. After all, I was about to get new axle shafts because that was the last link in the chain of possible problems. And I was growing weary of putzin around with this problem, besides, it was just a car show cruiser. What's the big deal?
In the end it got fixed, not with axle shafts, but with what an old timer told me at the tire shop..."put a different set of tires on it"
He was right, those brand new BFGs with 1200 miles on them had one square one. I swapped them out for Goodyear eagles and the car was so freakin' smooth it scared me. I watched those get balanced like 3 times, no wobble, no excessive run out, just a poorly built one. And that fix cost me nothing because of a warranty.
All that work for something that I couldn't imagine from the begining. A bad "brand new" tire.
So, the moral? keep it simple and save your self some money.
...
I am very familiar with tire vibration and what that is. I have been selling cars for 12 years and we always have tire issues. This is not a tire. The old tires that were 10 years old did it and now the new tires the same way. I actually think it might be the inter cooler scoop because it is slightly mangled or like a motor mount broken or trans mount broken, I just wondered if these cars had drive shaft issues or axle issues.
Thanks for all of the advice!:toot:
Thanks for all of the advice!:toot:
I've got a similar problem with my car. I was thinking driveshaft at first, but I've now ruled that out. Here's how:
In overdrive, run the car up to the speed you feel the vibration.
Manually downshift to drive and keep the car at the same speed, then determine if the vibration is different. You need to give the car some throttle as you downshift to keep the car at your desired speed and not shock the drivetrain too much.
If the vibration has changed, you know it is not the driveshaft because it will still be spinning at the same speed as it was in overdrive.
I would suspect my motor mounts or trans mount next. I know it is not a wheel or tire problem because I have two sets of wheels and tires and the problem is the same with either set mounted.
In overdrive, run the car up to the speed you feel the vibration.
Manually downshift to drive and keep the car at the same speed, then determine if the vibration is different. You need to give the car some throttle as you downshift to keep the car at your desired speed and not shock the drivetrain too much.
If the vibration has changed, you know it is not the driveshaft because it will still be spinning at the same speed as it was in overdrive.
I would suspect my motor mounts or trans mount next. I know it is not a wheel or tire problem because I have two sets of wheels and tires and the problem is the same with either set mounted.
