Engine vibration in a moving vehicle

[james_hernandezu]

At 75 mph, I'm experiencing high-frequency vibrations within the cabin. Before I had the tires rebalanced, I thought it was the new/used tires I had purchased, but now I'm not so sure.


I can completely eliminate the vibration by briefly releasing the thin pedal. Going 75 mph is bearable, but after you hit 85 or 90 mph, the speed becomes apparent. Even more frustratingly, things start to rattle all of a sudden. The car handles superbly at 65 mph.

Compared to when I had this car, I don't remember it doing this. Yes, I have driven this vehicle up to 110 mph (although that was a long time ago), and if my recollection serves me well, it maintained a firm handling and composed ride throughout.

Have you any idea what it is that I could be seeing? Is there an issue with the torque cable? Is that a bad mount?

[rafaelmk]

Is it possible to do it when stationary by pressing down on the brake and adding power? Does traveling uphill or downhill affect the beginning?

It felt relatively stable even at high speeds, as you mentioned."So, is it now being implied that it does not?" The sensation of being "unplanted" is difficult to put into words.

[james_hernandezu]

At the next stop, I shall give that a go. Going uphill or downhill doesn't change the sensation. It doesn't appear to be as bad going downhill. My guess is that it's because I'm reducing my throttle input when descending.

To compare the old and new feelings, "planted" probably isn't the right word. In comparison to how it felt before, I would describe it as rough now. The vehicle no longer seems to relish faster speeds, unlike when it did.

I'm wondering whether it could be a flex disk. They mentioned that the flex discs might be replaced during the previous inspection of the automobile, if I remember correctly. However, the standard for replacement at my shop is really poor. It's usual for them to provide us ballpark figures for our cars, say $8,000 or $10,000, from which I can choose.

[james_hernandezu]

Just so you know, Claude said that I probably shouldn't travel faster than 75 mph, especially when driving across the desert in extreme heat, just in case it's a flex desk. Seems like wise counsel. The additional MPG is also something I will not dispute.

[james_hernandezu]

Oh, I see another piece of information that could be helpful. The vibration frequency somewhat fluctuates as the acceleration reaches 80 mph or higher.

[rafaelmk]

A motor mount or exhaust hanger were my initial thoughts. The part of the powertrain that comes into contact with the body as a result of torque.

Crawling underneath to inspect the flex connections might be possible. I will surely consult them if the situation worsens. You would prefer not to have a damaged one when you're out on the road.

[felix_okaforp]

I think it's a good idea to check the flex discs. I lifted the back wheels off the ground and put my Volvo diesel into gear when I felt vibrations; I could see the drive shaft support bobbing up and down. Its bearing was damaged.

A small number of people have had the flex disc separating under load, which led to transmission tail shaft cracking and hosing off.
Take a look at the centering bearings on the drive shafts when you remove the flex discs.

Those flex discs that I altered.

[james_hernandezu]

Tomorrow morning, I will phone each of the stores on my list in San Francisco to see if they can get it fixed this week.

I know there's more to diagnostics than just looking at the motor mounts and flex disks, but they seemed fine.

[james_hernandezu]

So, I was hoping to find a facility that could fix this by Friday, so I'm planned to say 1) on a road trip when I call tomorrow morning. 2) I am experiencing vibrations in the drive line at speeds of 75 mph and beyond; these vibrations become worse as the speed increases. 3) I am very suspicious that the problem lies with the flex disks or center support bearing, or possibly the mounts; can you provide these parts quickly?

Is there anything else I need to emphasize to get their attention?