Diagnosing minor steering vibration

strother · 05-05-2005, 06:12 PM

I have an 82 SC, 46K miles, stock suspension. When I get to 80-85 mph, the steering vibrates just a little bit, but enough to make the steering feel a little uncertain. Is this normal with an SC?

The ride in the SC is otherwise nice, smooth, and tight. I can only feel it in the steering wheel.

scottb · 06:30 PM

First thing to check is the steering column bushing. It's made out of nylon, and over the years tends to disintegrate. To check the bushing, sit in the driver's seat, grab the wheel, and move it up and down and side to side. If you have play, then the bushing is bad. Our host sells a metal sleeve to solve the problem. It's about $15, and takes an hour or less to install. Here's a tech article on replacing the bushing.

If your problem isn't the bushing, then you should probably take your car in to a reputable tire shop and have them check the balance on your front tires.

I'm sure others will chime in with suggestions, but these areas are where I would start my inquiry.

Good luck.

Oh Haha · 05-05-2005, 06:34 PM

I have been trying to solve a vibration issue the past few months. I replaced the front suspension bushings, tie rods, and ball joints. Still there but better. I had the tires balanced a couple of times by different shops. I finally figured out that I had flat spotted a tire last year in a panic stop. Never even gave it a second thought before now. My tires were getting old anyway so I replaced them yesterday with new. Rock solid now!!
As with most problems, check the simple things first. When were your tires balanced last? How old are they? Over 5 years and they tend to do weird things. Good luck and post what you find.

lateapex911 · 05-05-2005, 06:39 PM

swap front to rear if you can as a test,,,does it get cyclical on long bends?

stuartj · 05-05-2005, 06:42 PM

Id tip an out of round or flat spotted tyre.

strother · 05-05-2005, 06:47 PM

It's tough deciding what information to post when you ask a question... I should have added the fact that I have tires with less than 100 miles on them. They were balanced incorrectly when I first picked the car up, and I took it back for rebalancing. (When they were out of balance the first time, there was a massive shimmy/shake in the steering wheel beginning at 60 mph.)

I bought new tires because the ones that were on the car when I bought it were 9 years old. And I flat spotted one at a DE.

I'm kinda assuming that the wheels are balanced correctly this time, since I already took it back for rebalancing once. Maybe I'm wrong? This vibration is a very minor vibration, but it is there. Because I've never owned a car whose suspension was this performance-oriented, I'm wondering if it is normal, and that I'm just feeling the road more at that speed.

And I can't switch front to rear to test, I've got much fatter tires in back.

stuartj · 05-05-2005, 06:55 PM

Still wouldnt discount it- its possible (less likely I agree) for a new tyre to be out of round. Tyre guys will tell -some tyres on some rims just will not balance. But its the easiest thing to check before you start on suspension and steering components.

Perhaps another tyre shop?- get them all checked for round and rebalanced. If no fix, start on the other areas.

lateapex911 · 05-05-2005, 07:01 PM

Too bad, because 911 steering is the MOST direct feedback there is. It would tell you right away if it is a tire or not.

Look at the bearings by shaking the top of the tire in and out. If you feel play, the bearings are suspect. If the vibration comes and goes, it would indicate a harmonic issue between the two front tires. Mine did that. It would be fine, but as I went around a corner, the outside tire would travel further, and the shimmy would get worse. It was a belt issue with one tire., and only solution was replacement.

Also check all the steering linkages for any play, as that will affect it as well.

Or, find a Pelican in your area and swap fronts for 30 minutes! I like to have a solid answer when I go back to a shop with an issue, or they can sometimes have you coming back a dozen times until it's made right.

Zeke · 08:54 PM

Look. Bushings, bearings, steering bushings and u joints don't vibrate. They are all slaves to the big thing spinning with all the weight. Yes, you will notice more shimmys and shakes if you have other issues, but a car with perfect tires will hardly show up other worn out parts unless they are simply junk. Not so good shocks will work, a little bit of slop in the steering will feel fine and old wheel bearings that are not making any noise won't even come into the picture.

Add a bad set of tires and any or all of these things could appear and drive you crazy. Yes, again, you want good parts in yout car, but the tires are the only connection to the road and they tell the story.

I have posted this numerous times and have had many others chime in with very good thoughts. The first thing you do with a new tire is match it with the wheel; heavy spot on tire over light spot on wheel. The 2nd thing is to spin it up and put a runnout gauge on the tread. 1/16 runnout is 100lbs out-of-balance (depending on tire/rim size) at 60 MPH. The thing is, it gets worse as higher speeds whereas the weight stays the same. this is due to tire expansion and the OOR spot now being further from the rotation axis.

YOu must have absolutey round tires or you will have OOB tires at some speed, usually higher the rounder the tires are. Tires must be "run in" a bit before truing them with a tire truing machine. this si the same machine you hear about on Tire Rack when they shave your tread for racing (and making them round). You have never driven on good tires until you have drivnen on shaved and erfectly balanced tires. the steering wheel becomes like one in a small plane while in flight.

Well, on to balancing the perfectly round and run-in tire. It must be dynamically balanced on a computer to offsett weight descrepencies fom side to side ot the vertical centerline of the weight mass. This means you must accept weights on the outside bead as well as the inside or be able to calculate how to place them just inside the spokes as for outward as possible.

Finally, the tires must be trim balanced oin the car with a strobe. Once dialed in, they should not be oriented on the lugs differently and definately not rotated. The man who taught me all of this holds several patents in this feild and claims if the car is properly aligned and perfectly balanced, you don't need to rotate tires or even rebalance them as the wear down perfectly.

Using his method, I have gotten some incredible mileage out of tire on my Porsches not to mention a perfectly steady steering wheel I could write a note on at any speed as long as the road itself was smooth enough.

I got over 60,000 on some Potenzas on the '77 Targa and I have 30,000 on the Continentals that came on the Boxster ans they show no signs of needing replacement anytime this year and probably into next. You don't see numbers like that often, but I will concede my wife drives these cars more than I do. Still, some tires wear out due to improper installation no matter how gentle you are with them.

stuartj · 05-05-2005, 09:05 PM

Excellent post, Milt

strother · 05-06-2005, 03:44 AM

Thanks, Milt. Very, very informative post. I'm storing it on my hard drive.

One of the many points you raise is that I have to accept weights on the outside bead. Of course, I told the shop to but the weights on the inside. I'll take the wheels back and ask them to rebalance them again, this time putting the weights whereever necesary.

jtratza · 05-06-2005, 05:12 AM

Excellent post Milt. I thought I had a tire problem recently. Turned out it was not but the point is the tire shop (Discount Tire on I-10 in Houston)was very willing to replace both tires if I wanted to give that a try. Turns out they love to supply tires and service to high performance cars in the area. If all else fails ask the shop that sold you the tires to replace them.

MAS · MAS's Garage

I had the same problem with my 77 a while ago. I got new tires (front and back), had them all balanced properly, and the problem vanished.

-MAS

Rondinone · 05-06-2005, 09:04 AM

Quote:

Originally posted by strother
I have an 82 SC, 46K miles, stock suspension. When I get to 80-85 mph, the steering vibrates just a little bit, but enough to make the steering feel a little uncertain. Is this normal with an SC?

The ride in the SC is otherwise nice, smooth, and tight. I can only feel it in the steering wheel.

IMO vibration is never normal. It indicates wear or imbalance somewhere in the suspension or wheel. Every time I've ever had a vibration that didn't go away with balancing, I have found either a bent wheel (2x) or worn shocks (bumper bounce test does not simulate driving conditions!) or worn suspension bushings (you may not be able to detect a worn suspension bushing with your arm or a crowbar).

A bushing, being somewhat of a spring, can couple harmonic motion. Tight bushings couple higher frequencies than loose bushings. As the bushings wear, the coupling frequencies change. If a bushing coupled a frequency that overlaps a harmonic resonance in your steering system, such as an imbalanced wheel, then you get vibration in the steering wheel.

Rondinone · 05-06-2005, 09:15 AM

Quote:

Originally posted by Zeke
Look. Bushings, bearings, steering bushings and u joints don't vibrate. They are all slaves to the big thing spinning with all the weight. Yes, you will notice more shimmys and shakes if you have other issues, but a car with perfect tires will hardly show up other worn out parts unless they are simply junk. Not so good shocks will work, a little bit of slop in the steering will feel fine and old wheel bearings that are not making any noise won't even come into the picture.

Add a bad set of tires and any or all of these things could appear and drive you crazy. Yes, again, you want good parts in yout car, but the tires are the only connection to the road and they tell the story.

I have posted this numerous times and have had many others chime in with very good thoughts. The first thing you do with a new tire is match it with the wheel; heavy spot on tire over light spot on wheel. The 2nd thing is to spin it up and put a runnout gauge on the tread. 1/16 runnout is 100lbs out-of-balance (depending on tire/rim size) at 60 MPH. The thing is, it gets worse as higher speeds whereas the weight stays the same. this is due to tire expansion and the OOR spot now being further from the rotation axis.

YOu must have absolutey round tires or you will have OOB tires at some speed, usually higher the rounder the tires are. Tires must be "run in" a bit before truing them with a tire truing machine. this si the same machine you hear about on Tire Rack when they shave your tread for racing (and making them round). You have never driven on good tires until you have drivnen on shaved and erfectly balanced tires. the steering wheel becomes like one in a small plane while in flight.

Well, on to balancing the perfectly round and run-in tire. It must be dynamically balanced on a computer to offsett weight descrepencies fom side to side ot the vertical centerline of the weight mass. This means you must accept weights on the outside bead as well as the inside or be able to calculate how to place them just inside the spokes as for outward as possible.

Finally, the tires must be trim balanced oin the car with a strobe. Once dialed in, they should not be oriented on the lugs differently and definately not rotated. The man who taught me all of this holds several patents in this feild and claims if the car is properly aligned and perfectly balanced, you don't need to rotate tires or even rebalance them as the wear down perfectly.

Using his method, I have gotten some incredible mileage out of tire on my Porsches not to mention a perfectly steady steering wheel I could write a note on at any speed as long as the road itself was smooth enough.

I got over 60,000 on some Potenzas on the '77 Targa and I have 30,000 on the Continentals that came on the Boxster ans they show no signs of needing replacement anytime this year and probably into next. You don't see numbers like that often, but I will concede my wife drives these cars more than I do. Still, some tires wear out due to improper installation no matter how gentle you are with them.

Yes, but suspension systems are designed to decouple small vibrations, and can hence tolerate some tire variation without it showing up in the steering wheel. MB and Porsche don't trim balance on the car at the factory, and they don't shave tires either. But my wife's MB cruises beautifully at all speeds, and so does my SC.

A really decent balance can be achieved using a Hunter road force balancer. Most upscale dealerships have one. It places a 1000lb load on the tire during the balance, and computes weight placement to minimize effects of radial variation. It will also tell you if you have a sprung cord, a flat spot, or a bent wheel. If your suspension is marginal and you don't feel like replacing bushings, this is an easy alternative.