Vibration Solution

[R.J.]

My car has a vibration that I can feel under the seat. It happens around 60-75 mph and gets worse when I get out of the gas and/or go over bumps. Here is what I have tried so far:
-Rebuilt rear end: backlash .010 and preload @18inlbs
-Aluminum drive shaft
-Alignment
-Wheels balance on a Hunter 9700 Road Force
-New rotors and pads all around

The guys that did my balancing noticed that the front tires are wearing unevenly on the inner edges. So maybe my shock are bad? My steering wheel is perfectly straight and does not vibrate. What would you guys look at next?

Thanks

 

[BobHyatt]

what about spinning the tires on the balancer and make sure there is no runout, either from an out of round tire, or something wrong with the rim (including bent/warped).

I can't think of much else that would do this.

 

[R.J.]

Yeah the Hunter 9700 Road Force balancer is the end all/be all of balancers and they were perfectly balanced on one of these machines. I was really wishing the balancing would have lead me to the problem!

 

[Dragstr05]

Yeah the Hunter 9700 Road Force balancer is the end all/be all of balancers and they were perfectly balanced on one of these machines. I was really wishing the balancing would have lead me to the problem!

Sorry to burst your bubble, but I have one of these at work and I did have a bent rim balance out just fine. I noticed it was bent as it spun on the machine, yet it says its balanced.

Check the lips on the wheels. Also check the sidwalls in the tires, if they're old you may have a break in the sidewall somewhere and they bubble out. The tires are the only thing on the car that contact the road, if your tires need replaced anyway and you cannot see anything obvious, start there.

 

[R.J.]

Now I have reinstalled the weight and rotated the D/S 180 deg. Still vibrates!!

 

[BobHyatt]

Yeah the Hunter 9700 Road Force balancer is the end all/be all of balancers and they were perfectly balanced on one of these machines. I was really wishing the balancing would have lead me to the problem!

You balance on that machine at a specific RPM. An out-of-round wheel or a bent/warped rim can be balanced at one specific speed with no problems. But you don't drive at just one speed, so it will be out everywhere else.

 

[Thundermouse]

The guys that did my balancing noticed that the front tires are wearing unevenly on the inner edges. So maybe my shock are bad? My steering wheel is perfectly straight and does not vibrate. What would you guys look at next?

Thanks

Be more specific on the kind of uneven wear along the inner edge of the front tires:
1)If the tire has patches of uneven wear along the inner edge, the your shocks are probably dead and you may also potentially be running too much camber.

2)If the tire is evenly worn-down along the inner edge as compared to the outer edge, then your shocks are fine and you are running too much camber.

Can you tell us anything more about the vibration you are feeling? Do you hear any sound along with the vibration? Is it engine speed specific? What happens to the vibration when the clutch is in? What happens when you are in neutral and the clutch is out? What happens when you are engine braking? Does your exhaust drone near that speed?

Are your exhaust pipes properly isolated? Are your spring isolators still in good shape? What about your wheel bearings, ball joints, and control arm bushings?

There's a million reasons you could be having a bad vibration, but the more information you give us, the better we can help you diagnose it.

 

[R.J.]

The wear is uneven on the inside row of tread on both front tires. Basically on that inner row, one chunk of tread is higher than the next then one might be lower and so on around the tire. Definitely not even at all, some of the tread on the inner edge is as good as the outer edge and the tires are only 8months old. I was told by the guy that balanced my tires that he would guess shocks from what he seen, BUT it could be just a worn front end part in general. I am basically looking for a second opinion. I’ve check my A-arm bushing, ball joints and wheel bearings, they have no play at all.
The Vibration:
-Sounds: Yes, sometimes a high pitch squeal, sometimes a hummm and sometimes both
-Engine speed: No, but vehicle speed yes. 60-75mph
-Clutch in: vibration does not change
-Neutral: vibration does not change
-Engine braking: vibration is at its worst
-Exhaust drone: No
-Exhaust pipes: well insulated (none of them are touching anything)
-Spring insulators are OK
-Brand new rear wheel bearings

Thanks for your interest.

 

[Thundermouse]

The wear is uneven on the inside row of tread on both front tires. Basically on that inner row, one chunk of tread is higher than the next then one might be lower and so on around the tire. Definitely not even at all, some of the tread on the inner edge is as good as the outer edge and the tires are only 8months old. I was told by the guy that balanced my tires that he would guess shocks from what he seen, BUT it could be just a worn front end part in general. I am basically looking for a second opinion. I’ve check my A-arm bushing, ball joints and wheel bearings, they have no play at all.
The Vibration:
-Sounds: Yes, sometimes a high pitch squeal, sometimes a hummm and sometimes both
-Engine speed: No, but vehicle speed yes. 60-75mph
-Clutch in: vibration does not change
-Neutral: vibration does not change
-Engine braking: vibration is at its worst
-Exhaust drone: No
-Exhaust pipes: well insulated (none of them are touching anything)
-Spring insulators are OK
-Brand new rear wheel bearings

Thanks for your interest.

Yep, shocks are gone. Replace those and then let's work from there.

 

[R.J.]

What a coincidence I was actually pricing and comparing some Tokico Illum 5-ways and some Bilsteins today. Looks like I’m getting some Tokico’s. Every body seems to love the quality and warrantee of Bilstein but the ride seems rough to most. Now I just have to figure out how to pay for them!! Do you think this could be part of the vibration? I was thinking I had two different issues?

 

[DTNODYA]

Check your motor mounts. I had an issue similar, it almost felt like the driveshaft was shaking right under my seat. It took me FOREVER to figure out that it was my motor mounts that were shot. The engine was sitting lower because of this and it caused the trans, driveshaft, etc, to be crooked. The driveshaft would sometimes rub the e-brake bracket and other times it would just feel like it was binding (at about the same speeds you are having issues with).

May be an alignment issue but if the steering wheel isn't shaking then it kinda rules it out IMO.

Food for thought ..

edit: Shocks could be the culprit too now that I think about it ...

 

[R.J.]

My local Mustang shop said to try front wheel bearings before I spend the money on shocks. They have seen a couple of 99-04's have bad bearings that showed no signs of play or movement. So I ordered some.

 

[steve_stang2003]

My local Mustang shop said to try front wheel bearings before I spend the money on shocks. They have seen a couple of 99-04's have bad bearings that showed no signs of play or movement. So I ordered some.

Before you replace shocks have someone drive next to you and look at your wheels to see if they are bouncing around. This is also a good check for a bent axle.

As for U-Joints, put two people in the backseat and drive around and see if the vibration changes. The extra weight will change the driveshaft angle and usually either aggravate the problem or make it go away.

FWIW I fought a vibration problem similar to yours on a 79 Chrysler RWD car and went through all the same kind of stuff.
It ended up being a sticky rear wheel brake cylinder/spring/etc in the drum brakes. It would also get me in the seat of the pants and in my case it was intermittent but happened enough to drive me nuts.

I feel your pain because I know vibrations and weird noises are some of the most difficult problems to troubleshoot.

 

[2002GreyGT]

As for the Hunter machines, I have also seen a bent rim (mine) come out perfect on these machines, that what they are made to do is help balance tires good or bad. Usually I watch for the rim or wheel to HOP when its spinning to see if there is any out of round or bent rims, etc.

Also what was your road force measured at on the hunter? They may say its passing, but for instance 16lbs of force would not show up in a passenger car, but you will feel 16lbs in a mustang...especially if you shocks are going.

Have you checked to make sure you back rotors are not warped?
How lowered is you car? You might need some CC plates to straighten her out.

Also try a different shop to balance the tires, the machine may be good, but the tech you never know. Those machines are supposed to be serviced and checked I think, my shop has had to get theirs repaired a few times before.

I had my tires balanced on a hunter before a road trip and thought they would be good, but after about 80 miles I found a different shop and got them done again, some where out as much as .75oz. After the next shop did it, it drove like a dream.

Start cheap and work your way up.

You can always swap rims with a friend to see if its in your tires / rims.

~K

 

[R.J.]

I have steeda sport springs with CC plates.
back and front rotors are brand new and have no runout.
My highest road force was 24, what does this mean?
Thanks