Tires out of balance or what?
 

My 1984 190d at about 40mph started to shake a little bit - you know, like the tires are out of balance. I took her to have the tires rotated and balanced. The slight shake is still there, but at different speeds - 55, 45, 60, etc. Now, while I'm driving, say at 55 she shakes a little. I slow down and get back up to 55 and she's as smooth as silk. I guess what I'm trying to say is that some times she will, and sometimes she wont. When I had the work done I just mentioned I took her back because I thought they did not get the tires in balance. So, they did it again. If its not the tires, what in the world could be causing this??

Sincerely,

Hugh

shaking
 

I've had the same problem at high speed and went thru the tire balancing and rotation etc. like you are doing, at the end the problem went away when I replaced the steering dampener... My 2 cents

Shakes
 

Definately the steering dampener. Check the tie rod ends and Pitman while you're under there.

The steering dampener nor any other part in the front end can CAUSE a vibration. Bad parts can allow a vibration to be exacerbated, but only ROTATING parts can CAUSE vibrations.

The most common cause of vibrations are indeed tire related. Of the tire related causes, the most common cause is when the tire store kids do a static balance rather than a dynamic balance. A static balance involves putting a weight on the inside lip of the wheel only. This will prevent the wheel from hopping up and down, but on todays nimble suspensions this is not good enough.

A dynamic balance uses wheel weights on the inner and outer plane of the wheel and prevents the wheel from wobbling. The tire store kids avoid this because they get yelled at when they scratch alloy wheels with wheel weights. To dynamic balance WITHOUT scratching alloy wheels, a savvy wheel balancing tech will use tape weights just behind the spokes of the wheel for the balance of the outer plane.

If your tire store gives you a blank stare when you tell them that you want your wheels balanced this way, find another tire store.

As far as steering dampeners and other front end parts, I would not replace them until I got the vibration to go away. That way you have a system that will more easily tell you when a wheel is out of balance. Once the wheels are properly balanced then, of course, find and repair any loose or worn front end parts.

Good luck,

Shake
 

I agree with Larry. It could be poor balance. I got 4 new Goodyear tires recently, and the car shook as out-of-balance, yet the tires were spin-balanced on an electronic balancer. Found someone with a Hunter machine which measures road force (actually rolls the tire under load to check for uniform stiffness) and one new tire got junked.
My 420 was extremely sensitive to shake, to the point it was not drivable at speed, until I changed the steering damper; the old one offered no resistance when moved by hand. Everything fine now.

I would add that warped rotors will add to the harmony of vibration issues...

...though I have a number of front suspension parts that need attention, replacing the wheels,tires and all sorts of balancing did NOTHING to reduce the highway-speed vibration issues...until I finally replaced the original rotors on the car. Vibration reduced by about 95%!

It seems to me rotors would cause a vibration only when you braked. That's how I knew my rotors were shot in another vehicle. they were barely within spec, but got slightly warped.

Changed rotors, no problem.

I agree with the balance situation. I have had many tires balanced and it has been years since I have had a balance problem...and I dont' get tires balanced at any fancy place. I hope your ball joints or tie rod ends are not really, really worn.

Larry,
I've pretty much always agreed with you on most posts, because you are a professional and know your stuff, but I'm going have to disagree with this one. I too was tought during my apprenticeship that a loose front end component could allow shimmy but not cause it. I've had a couple of times and a 91 4matic wagon in particular where I couldn't find anything wrong. The steering shock on the wagon wasn't too yippy skippy, but I couldn't see how that could cause the intermittent shimmy. In desperation I changed it, and the problem disapeeared. I know, Larry, just when we think we know something, they change the rules.:D


Randy,
High speed tires are rated at higher speeds, because they are designed to control expansion at higher speeds. A tire will balance fine on any old balancer, but when the tire starts rotating at speeds that make the tire want to fly apart, an area of a defective tire will actually go out of round causing a deformity in the tire at high speeds. That special Hunter balancer you mentioned can detect the defect. It is funny you mentioned Goodyear, because that is one tire company that has had a problem in this area. For normal everyday balancing almot any balancer will work fine unless you encounter this problem. Then you need to seek out the Hunter. In fact my wheel balancer is a Snap-On that doesn't even spin the tire. You reach down and spin the tire a few revolutions by hand and wait till the LEDs tell you where to put the weights. I also have a Sun high speed balancer, and I don't see any difference between the two. Hope this helps.

Autozen,

I have seen something similar to what you describe in the case of the dampener correcting the vibration. This is a very unusual thing to see happen. In the case where I saw it, there was a combination of alignment anomalies that were causing it. If I remember correctly it was a previously crashed car that was way out in camber and a little toed out. The combination seemed to put the front wheel in a bind while going down the road straight and was causing the wheel to shimmy in and out.

Such an odd situation can cause all sorts of weird things to occur, but typically if the wheels and tires are properly balanced, no excessive RFV or lateral run out, you can take the dampener off and throw it away and not be able to tell the difference. That's just what I've found.

As with anything, there are almost always rare exceptions to the rule.


As far as todays Goodyear tires go, I would run wheels off of a covered wagon before I would spend my hard earned money for Goodyear tires. If I were going to sell Goodyear tires I would make DARN SURE that I had a GSP9700 in the shop with a maintenance contract on it because I would probably wear it out in short order.


BTW autozen, I know the Snap On manually turned balancer that you are talking about and I think that it is an OUTSTANDING unit. It does the very same thing as most any other spin balancer and does it in the same way. The difference is that you don't have an expensive drive motor to repair/replace/rebuild. The computer balancers don't need to spin the wheel fast to resolve the balance. I expect that they will work as good or better than any computer spin balancer. I have an old Coates 1001 and love it, mainly because I have learned how to fudge the settings for different situations such as using tape weights behind the spokes for balance of the outer plane. I would like to have found a Snap On like yours because not only does it do a great job, but I love the simplicity of these units.

My $0.02,

Getting a little off topic here, but my recently purchased Goodyear tires say " Made in Slovakia " on the sidewalls. :confused:
So far, so good.
On the steering dampener, it's always been my understanding, the function of it is to " soften", i.e. dampen the steeringwheel movement, whenever the frontwheels travel over bumps/ripples in the road.

I'm no pro, but I've certainly fought my share of vibration problems over the years. Most dampers aren't that expensive, so if the car has the miles, it could almost be considered a maintenance item.

In the majority of my cases, it turned out the be the result of tires with faulty belts - on brand new tires, on tires with 20k miles, and with worn tires.

Even if your wheels are properly balanced - statically and dynamically with weights on both sides - and the machine reads zero-zero on the check spin there is always a slight residual static and dynamic unbalance because modern machines only balance to within about 2-3 in.-oz.

I KNEW my steering damper was leaking, but I put it off, and the car on a couple of occasions went into the worst front end shimmy I have ever experienced, and the wheels were in good balance. Shame on me. That steering damper (not dampener or dampner) is there for a reason and an IFS with a lot of caster needs one.

If the damper is leaking, it needs to be replaced ASAP. It's also easy to disconnect one end and test it. Gas pressure should expand it and it should take a good 20 pounds of force to slowly compress it.

If it's leaking or limp - REPLACE IT!

Duke

Larry,
Snap-on likes to take credit for the concept, but I remember seeing a German unit at a local dealership about 25 years ago that operated the same way. I was awe struck at the time. Interestingly I was talking to a seasoned mechanic yesterday, and he said he can match any high speed balancer in a closed room with no drafts and a bubble balancer. I believe him and wouldn't put any of my money up to challenge him.:D

Your mechanic friend is correct in that he can achieve a STATIC balance with a bubble balancer as good as STATIC balance achieved by a spin balancer, but it is impossible to do a DYNAMIC balance on a bubble balancer.

I do believe that he can achieve a static balance with his bubble balancer that is equal to a static balance on a spin balancer, but that is not NEAR good enough with todays resilient suspensions.

Static balance only keeps the tire from hopping up and down while a dynamic balance given by a properly operating spin balancer, keeps the wheel from wobbling. If you only do a static balance for a wheel that is going on a Benz, you will have a vibration unless you are VERY lucky.

Have a great day,

That's always been my thinking. A bubble balancer will take out a heavy spot radially, but I don't see how it can differentiate axially. Again I wo't argue with him. I'll just keep using my spin balancers.:D

A tire/wheel can be in static balance, but not dynamic balance. Mathematically dynamic balance means the angular momentum vector is not coincident with the axis of rotation, which will make the assembly want to wobble, and wobble can induce shimmy without adequate damping.

That's why Mercedes high caster suspensions have steering dampers.

Dynamic unbalance became more critical as the aspect ratio of tires was reduced (larger width to sidewall height ratio) and wheel width increased to match the wider tires.

Many think that the old on-the-car spin balancers offered dynamic balance. NOT TRUE! They only statically balanced the assembly.

Dynamic balance requires the tire to be balanced across it's width. An assembly can be in static balance, but not dynamic balance, but not vice versa. In order to achieve dynamic balance weights are required on both sides of the wheel, except for rare cases.

I have one wheel/tire on my Cosworth Vega that read zero-zero without weights. We even rechecked it. My guy said he's seen that before, but it's very rare.

Duke

Can rotors cause vibration at speed?
 

While on balance, vibration and front end components, I recently installed a new set of front rotors - Balo - on my 1990 300E 2.6 (95K). I was careful to thoroughly clean the hub so as not to leave any residue that might cause uneven setting of the new rotors. While installing one of the rotors, I noticed what looked like a "V"-shapped piece of the metal missing from one of the interconnecting "webs" (probably not correct term). The edges where the piece was gone were very smooth - not jagged like they might be if a piece had been broken out. Thought the missing piece might have been machined out to achieve balance. After installation, I noticed a very slight vibration around 55+ mph that had not been there before. I don't believe this is tire related because I had the tires re-balanced, then a new set mounted and road-force balanced. The pedal also does not feel quite right - a barely perceptible bit of pulsation at times, almost as though there is a VERY SLIGHT warp of the rotor. Again, I thoroughly cleaned the surfaces and was careful to torque everything to spec. Is it possible for a rotor to be out of balance? Is some metal machined from the web during the manufacturing process to achieve proper balance of the new rotor? I discussed this with someone who said he has been involved with NASCAR and he said he has never heard of a rotor being out of balance or of how to check the balance on a rotor.

Oliver,
Ithink you got a defective rotor.

Duke,
If you say the weights have to be on both flanges of the rim, I will have to disagree with you. Your theory may be correct and scientific, but for all practical purposes weights on one flange are all that is necessary even for folks like me who like to open it up across the Mohave Desert on the way to Vegas. The only person I know who might be concerned with your theory is my neighbor who lives 20 miles away. When he runs his car it is around 600 MPH and he has special tires that are Kevlar rapped.

oliverb

It s not unusual to have a rotor with some of the ventilating vanes machined off at the end.
That's an indication it was necessary to achieve balance.
Autozen could still be correct though. ;)

It's not a theory. It's basic physics.

If you don't mount weights on both sides the assembly is probably not in dynamic balance, which may or may not cause a problem.

There is insufficient room between the wheel drop center and brake caliper on my Cosworth Vega to mount stick on weights, and I don't want to marr the outside of the wheel with weights, so I only have them statically balanced with aluminum wheel clip on weight on the inside flange. Since the wheels are only 6" wide with 205/60R-13 tires, dynamic balance has never been a problem. Dynamic unbalance is be indicated if the steering wheel wiggles right-left a bit at certain speeds.

As wheel and tire width go up, dynamic balance becomes a greater issue.

On my 190 I have the tech mount stick on weights on the wheel drop center just inside the outside face. Modern equipment has probes that provide the machine with the distance of the weight planes from the wheel center plane and also the radius of the weight from the axis of rotation. Both these dimensions are required so the machine can calculate the required weight for dynamic balance.

Most who have not been exposed to an engineering course in dynamics do not understand dynamic balance. The angular momentum vector conincident with the spin axis is the easiest way to describe it, but from a practical point, if the steering wheel doesn't wiggle back and forth, any dynamic unbalance present is not sufficient to cause problems. In the case of Mercs, this is true IF the steering damper is okay. If not, get ready for some serious front end shimmy.

Duke

Duke

I have to agree with Duke on this one. It is certainly possible to get lucky with a static balance using weights only on the inside rim. In my experience if you are using Michelins or Kumhos you might get lucky because I have found that these tires typically require a very small amount of balance weight.

Even in a case of a tire that requires a small amount of balance weight if you don't DYNAMICALLY balance both planes the wheel will have wobble and on a nimbly suspended car such as most any MB built in the last 30 or 40 years you will very likely get a vibration.

Static balance will keep the wheel from hopping up and down and is better than nothing, but a proper two plane dynamic balance will almost always eliminate vibration.

autozen, since you only use weights on the inside rim, you may very well lose money to your friend. If you are only using your spin balancer for static balance you are doing no better than can be done with a careful bubble balance job.

Have a great day,

Peter, I also agree with Duke on this one.

As a person who has been involved with balancing jet engines for 25 years, the proper way to balance an automobile tire and wheel assembly is by the use of a dynamic balancing machine.

"Dynamic" in this sense is the combination of "static" and "couple" unbalance. Static unbalance is a single force acting through the center of gravity of the object that effectively displaces the C.G. from the axis of rotation. It can be corrected by a single weight placed in the plane of the C.G., or, in the case of an automobile wheel, by two weights on both flanges, at the same angular location.

Couple unbalance is an equal and opposite force acting on the object. The C.G. remains on the axis of rotation, however, the principal intertia axis is not parallel to the axis of rotation. A wheel that "wobbles" on a spindle would be a perfect example of couple unbalance.

All automobile tire and wheel combos exhibit a combination of static and couple unbalance. Naturally, the static unbalance component is the most important part of the balance because the forces transmit straight into the spindle. The couple unbalance will produce less force because it is dependent on the distance between the couple legs. So, the forces acting on an 8" wheel will likely be greater than those acting on a 6" wheel.

A modern tire balancing machine can sense both static and couple unbalance and provide the correction required to achieve "zero" unbalance. Please note, however, that these machines are relatively crude and do not have much capability of seeing unbalance that is less than 2 oz.-in. The machine has software that automatically displays "0" when the machine gets below this "magic" number.

Just for comparison, some of my jet engine components weight 250 lb. and the balancing machine is capable of reading the unbalance down to .1 oz-in. in each of the two correction planes. A similar machine, if used on an automobile tire, could measure and display readings down to .02 oz.-in. in each of the two correction planes.........fully 100X more sensitive than the machine in the tire store!

autozen,

I hope you don't think that I'm trying to be combative about this. I am just trying to show you the difference in static and dynamic balance. For years I got by with static balancing using a bubble balancer. My first 240D in 1977 gave me fits the first time I tried to run wheels balanced on a bubble balancer. That's when I became acquainted with dynamic balance and I am a huge believer. I feel that it is absolutely mandatory on modern cars with nimble suspensions such as the 123 and newer MB cars.

The article explains this well and has diagrams that will help show the difference.

http://www.gsp9700.com/pub/technical/4202T/6GLOS003.cfm

Have a great day,

I appreciate all you guys being considerate of my professional standing and not flinging me up against the wall. It turns out I am in total agreement with the concept of dynamic balance. I misinturpreted Duke's comment about two flanges to mean two spots on the flange. At my age brain f*rts come far too often. I'm well aware that wheels with KPI need static balance to eliminate front wheel tramp and dynamic balance to eliminate wobble from the wheel changing direction along its axis. Wheels that always remain in the same plane only need static balance.

I pride myself on reading posts very carefully and picking out details that others miss. I guess I blew it on this one. Sorry guys.:o

........ahh, when you get to be our age........all is forgiven.;)

As an addendum: I do not use a bubble balancer. I merely commented on a former shop owner turned Snap-On dealer who commented he could match a high speed balancer with a bubble ballancer. I have a Sun high speed balancer and A snap-On hand crank balancer. I really like the Snap-On machine and have loaned my Sun machine to another shop.