Violent Shake

[svttouruofl]

I have been having a problem at very high speeds with the car shaking violently during a certain speed range. It smooths out once I get above a certain speed...What would cause this and what should I check on my car?

 

[Tony2005]

..at very high speeds with the car shaking violently during a certain speed range. It smooths out once I get above a certain speed...What would cause this and what should I check on my car?

Some of the things which can cause this are:

1) Engine/tranny mount. (inspect visually)
2) Lower Ball joint (2 and 3, do the o'clock test and push pull on wheel with one side of car on jacked up.
3) Tie rods.
4) Wheel bearing (but usually with a roaring sound).

Edit. O'clock test

Jack up the car one side. Place on jack stand.

Grasp wheel at 12 and 6 o'clock and push in and out. Any movement, most probably suspect wheel bearing.

9 and 3 o'clock - tie-rod/ball joint.

Lower the car and do the same for the other side.

 

[SvtTour98.5-3]

Generally, I've found tire balance to be the culprit for this situation. Starts shaking around 50 MPH or so and smooths out around 60-65 MPH. If the above doesn't take care of it, you might want to look at your tires.

 

[Big Jim]

Generally, I've found tire balance to be the culprit for this situation. Starts shaking around 50 MPH or so and smooths out around 60-65 MPH. If the above doesn't take care of it, you might want to look at your tires.

I agree, the first thing to check is the tires, wheels, and tire balance. An out of balance tire and wheel can have a horendous shake, usually most noticable at roughly 55 to 65 mph.

You may have a tire with a bubble, a badly worn tire with cord showing, a tire with internal problems that went out of balance as it wore, a bent wheel, a wheel that is hard to balance due to design (many good looking wheels won't balance well), a wheel that won't properly center on the hub (hubcentric adapters are needed with some wheels), a tire that never was balanced well, or any of a number of other problems.

 

[svttouruofl]

I dont think that the tires are the problem...I purchased some rims recently and have basically new tires...I'm not allowed to say at what speed this happens at do to the posting rules(one thread was already deleted) but it starts shaking at double the speed you mentioned that it smooths out at and my car car smooths out about 10-15mph after that....if thats any help.

 

[Big Jim]

Put the old tires and wheels back on and see what happens.

Out of balance vibrations come in multiples of 1700 RPM (speed of the item out of balance). That would be 1700 RPM, 3400 RPM, 5100 RPM, and so on. Sometimes it is mild at the first harmonic (1700 RPM) and harsher at the higher ones.

If it isn't the tires and wheels, look for something the rotates at about double the speed of the wheels. If it were something engine related, it would be present when you rev the engine in any gear when you hit the problem engine speed. It would also be present (but perhaps not as noticable) if reved while parked and out of gear.

If this started immediately after installing the new tires and wheels, I'm betting that it is tire and wheel related.

 

[Tony2005]

....a wheel that won't properly center on the hub (hubcentric adapters are needed with some wheels), ....

......I purchased some rims recently .....

If you installed aftermarket rims, first check on what Big Jim posted. That was usually the problem in previous times.

And yes, usually it smoothens out after a certain speed. Then if and when you do get to an additional increased "band", you will get the the massive vibration again. But you won't get to that speed as the SVT can't get to 180 MPH.

 

[svttouruofl]

I think that is what it was to because I was around 5Krmps when it started and it smoothed out just before 6K. But this was in fifth gear...Why haven't I ever had this happen in lower gears?

O and about the rims I have had them for about 4 months.

 

[Tony2005]

I think that is what it was to because I was around 5Krmps when it started and it smoothed out just before 6K. But this was in fifth gear...Why haven't I ever had this happen in lower gears?
....

I have the same problem (at 2.75 to 3K RPM). But I suspect it is something else for me.

As for your question, I suspect it is due to vibration of the engine and resonance created at certain speeds. Kinda like the "moose" that most of us have to deal with. I will PM you some info.

Edit. Link to resonance.
http://www.lightandmatter.com/html_books/3vw/ch02/ch02.html