Vibrations at very low speed. Why? What to fix?

[velozi]

So here is the issue; when I drive between 3-6 mph my car begins to vibrate. Nothing major but I am about to tackle the rear suspension and would like to hit this problem at the same time.

It is not the engine: even if I rev it the shaking continues.
It is not the transmission: I tried first, second, third or coasting and same shakes.
Same driving straight or taking a curve.
Same with old or new correct differential fluid.

If I slow down it goes away, if I accelerate it never happens until I slow down and hit 3-6 mph.

Most time you do not feel it but if I keep it at the same speed it goes for the entire time.

Something is unbalanced?

Let me know when you think.

[Pete112]

Sounds like an out of balance tire to me. Sounds so simple, but that's what all of those symptoms point to. Not much is turning at the same speed under all those conditions. Really just the tires and driveshaft.

Easy elimination too. Try rotating them to see if it makes a difference or swapping out the spare for the tires.

[mbouse]

if you are a tire eater like i am, you would be amazed at what changes in handling when you do a five tire rotation a couple of times a year. i will do this (rotate all five) for every oil change, and again if i go to a show (with my cromadora rims going on for the show, and the OEM steel wheels coming off only for the show).

BTW - Karl, if you are reading this, i actually check the tire pressure EVERY time i do this rotation.


speed limits are for establishing the lower perimeter..
drive it like it's stolen!!

[kmead]

[racydave]

It sounds alot like a busted belt in one of the tires. Easy to diagnose, just jack her up, and spin the tire, youll see the wobble.

[ga.spyder]

I agree with Dave.My daughters car recently developed a low speed ''death wobble''.One of the tires had internally come apart.Plenty of tread and not a real old tire,either.
Craig

[velozi]

So I changed the tires/wheels, balanced everything, new brake rotors, checked all drivetrain components for wear, check condition of trailing arms, lookes at bushings... All looks fine.

But still the same strange vibration at very low speeds from the rear. No problem at all at higher speeds.

What now?

[HOLLYWOODSPIDER]

Since you've isolated it to the rear end, have you checked the differential and u-joints closely? Just a guess at this point, but maybe a worn input shaft bearing?

[ITA124]

But still the same strange vibration at very low speeds from the rear. No problem at all at higher speeds.

The reason you don't feel it at higher speed is the frequency is too high. I would run down the drive line components, isolate and check.
- Rubber doughnut
- Prop shaft centre support bearing
- Universal joints
- Diff input shaft (loose).
- Drive shafts bent.

When, or if you removed the rear brakes have a look for a brown coloured fluid weeping near the flange. This is an indication that the shaft brearings has gone. Another possible source of vibration.

Good Luck

[carl55]

You could try jacking up the rear, put it on jack stands, start the car and put it in gear and see what is vibrates.

Carl

[majicwrench]

Ita is on the right track. It is not a tire vibration, those show up at higher speed. At 3-6 mph tires are barely turning.
To vibrate something with some mass has to be spinning out of balance. Would be odd to see a driveline- ujoint issue at that speed, but driveline is spinning about 3.5 times faster than tires are, so a driveline vibration tends to show up at a lower speed, but usually that means 40mph.
Good luck

[ITA124]

You could try jacking up the rear, put it on jack stands, start the car and put it in gear and see what is vibrates.

I would not advocate this. My question is, what are you going to see? No one in their right mind is going to snoop under a car while it is running on jacks. Needless to say that you are sourcing a vibration that may oscillate the jacks and perhaps the car off.

Safety First guys. The car is not worth it.

[baltobernie]

Some tires use materials and construction that allows them to "dent" when parked for an extended period of time. Since our Spiders are usually driven infrequently, this may be what you're experiencing. Some classic car owners even park their car on cupped trays made for this purpose in order to eliminate this tendency.

The problem seems to be most noticeable on vintage tire designs, but I even see (feel) it on newer cars, but the thump disappears by the end of the driveway.

If you've inspected the undercarriage to your satisfaction, I'd try and swap wheels/tires with another Spider for a test drive. Unless your tires are more than six years old, in which case you should replace them regardless.

[velozi]

Finaly found the low speed vibration problem. Unbalanced drive shaft with a worn center bearing.

Began getting worse and a metal sound appeared. Looked under the car and found the sharft hitting a seat belt bolt.

INext step is to take out the entire shaft, balance, paint and replace all joints.

[Zippy]

Glad you found the problem. Thanks for posting the the result. Often we hear a complaint about a problem and suggestions are made as to the cause but no folllowup is provided.

My first thought was about the tires, too. We had a Subaru awhile back and on a trip back from Santa Cruz our kids kept complaining about the car shaking. I pulled into a parking lot and walked behind the car as my wife drove it slowly and you could see the back end shake. I looked at the tires and saw one was bulging in one spot. I put the spare on and the shaking went away.