Chasing Down Vibrations and Ride Quality

[Mike1261]

I bought an 03 GT with 158k and TR3650 last summer.

By the time I got it home the throwout bearing went bad so the car sat till Jan when I changed the clutch, tires, shocks & struts (Tokico) and Eibach Pro-Kit springs.

Finally I got to drive the car, and I noticed that with the top up I could suddenly hear and feel lots of things that I overlooked with the top down.

The transmission makes a lot of noise. I'm sure it needs a rebuild at some point.

But the most annoying is how much the car shakes and vibrates going down the road.

It gets worse over 45-50mph. I don't really drive highways around here, but if I did it would be unbearable.

The vibrations DO NOT change when the clutch is pushed in. It also DOES NOT change with the Transmission in Neutral.

I was thinking maybe the tires are cheap (but new) and maybe not the best quality. Perhaps a Road Pressure balancing would help.

Unfortunately I made all the modifications at the same time so I can't say whether or not it had vibrations with the old bald tires. But when I bought the car I drove it top-down which makes vibrations and noise disappear, and the shocks and struts were toast so the car drive like crap anyway.

I've rotated the driveshaft into all possible positions in case vibration subsided at all. No luck.

I considered motor mounts, but clutch down and transmission in N, no change at all even when revving up the engine. Smooth as buttah..

Where do these SN95's typically develop their vibrations? Where would you start with diagnosis?

 

[ttocs]

when was the last time the alignment was done?

 

[white95]

Could be a worn transmission mount or one of the engine mounts transmitting unwanted vibrations through the chassis but you thought of this already.. I’ve never had a convertible but I know they’re leas structurally rigid than their coupe brethren. Does the car have aftermarket subframe connectors? Have you checked for worn control arm bushings? That could lead to some unwanted suspension movement and vibrate while moving. Does it get better on smooth roads?

 

[DKblue98GT]

When I first got my car it had worn out motor mounts but the only time I noticed a vibration was accelerating on the highway. From about 45 on the car would vibrate if I got on it. No vibration at low speeds.

 

[delling3]

I have had my '96 GT VERT for about a year. It is my first/only Mustang, so I have a pretty narrow frame of reference. My car's suspension is pretty much stock at present. It is a California car, and has been garage stored it's entire life, so it's been babied a bit (no snow, no salt, etc.) I replaced the tires/shocks/struts when I purchased it with around 95,000 miles on the odometer. I also had a set of Steeda full length SFC's installed. It came to me with a front shock tower brace installed.

Tires and shocks/struts really made a huge improvement in ride quality/road noise/vibration. The SFC's helped stiffen up the chassis, which is noticeable operating over Michigan's notoriously bad roads. When I do find a stretch of decent pavement, the car is very smooth and quiet. Operating on uneven pavement, cowl shake is very noticeable.

My experience is similar to yours with regards to interior noise - particularly with the top up/windows closed. A lot of this is (in my opinion) due to the large expanses of cheap plastic used on the interiors of these cars. The interior door panels, and rear seat trim panels flex and drum against the interior sheet metal (inner doors, etc.), creating a "booming" sound. The door pulls are hard plastic and don't have a particularly tight fit in the door panels, resulting in squeaks and rattles. Same for the console components. Cheap crap.

I am thinking of getting some Boom Mat - or similar, and installing it between the door panels and rear seat trim panels, and the body. This should help reduce and deaden the noise.

My other "solution" is to avoid driving the car with the top up I have that luxury though, as it is a toy for me, and not a daily driver. It rarely leaves the garage if it isn't "top down" weather.

 

[DKblue98GT]

My other "solution" is to avoid driving the car with the top up I have that luxury though, as it is a toy for me, and not a daily driver. It rarely leaves the garage if it isn't "top down" weather.

Me too!

 

[ttocs]

when you say it shakes, do you mean the steering wheel shakes? The rear end shakes/drifts? The front end shakes? You need to narrow the area down. Year ago when I had my ranger I started to notice that the wheel would shake mainly under light braking at moderate speeds. It turned out to be that the steel belts on the front passenger side tire separated and made bubble on the inside of the tire where I could not see.

 

[Mike1261]

So it turns out that the reason I had trouble narrowing down the shaking, was because the shaking was EVERYWHERE at ALL speeds.

Solution: $22 for a pair of U Joints and an afternoon with a BFH :-D

3 of the 8 bearings were bad, and I've attached a pic of the really bad/bone dry/fell completely apart in my hand bearing lol.

The worst bearing was the front bearing. Now with new U Joints, dash rattles, shifter shake, sideview mirror shake, and 75% of the reasons I hated the car were cured.

Our daily is an 06 BMW X5, which has had its own long list of fun things I've fixed, and the Mustang really is just a winter car (Florida rains too much all summer to bother driving a convertible lol). So I've put less than 500 miles on the car since I bought it. Now with a freshly charged AC and new U Joints, I'll probably take it out more.

Next weekend project is to line the car with sound deadener to make that exhaust drone more tolerable. Never was a fan of Flowmaster, but I'm not paying for a new exhaust at this point!

Thanks y'all for all your feedback and food for thought. There's a lot more to do to this thing to get it to where I want it, but this $22 fix went a long way!

 

[white95]

Good catch!!

 

[lutter94]

I have over 200k miles on the original u joints. Should prob look into swapping these at some point......

 

[myk]

Doesn't anyone test drive or inspect cars before buying them, anymore?

 

[delling3]

I know the OP solved his issue with new U-joints, but I discovered something on my GT Convertible today that I thought I would pass along. As noted in my earlier post, my car is kind of noisy on rough pavement. The noise is interior noise - which I attributed to the plastic trim panels flexing and banging against the inner sheet metal. This morning I drove the car (top down) over a stretch of pavement, and dealt with a lot of noise. A few hours later, I drove over the same section of pavement with the convertible top boot installed (it was left off earlier) over the same stretch of pavement. The difference in interior noise was very significant. Maybe the noise I had heard was the folded top banging around, or maybe the boot dampens out some of the flexing of the rear seat trim, but regardless of which, the car is noticeably quieter with the boot on. Just a tip for you vert owners.