Bad vibes

shuzboomer · shuzboomer's Garage

Hello Friends,

I am trying to sort out a front end vibration that occurres while driving at highway speeds. The vibration is felt directly through the steering wheel but the car does not drift or pull if the wheel is released.

The vibration actually gets less pronounced when I run over 80mph, and is most noticible at around 60mph.

The car was taken to a local porsche wrench, who suggested balancing the tires... 60 bucks later zero improvement.

The car is an 86 targa with little to no history. Most if not all suspension is stock. We have 130k on the clock.

Tell me where to start.

Thanks!

RBL

mreid · 10-25-2013, 07:41 PM

Ball joints, tie rod ends, steering rack are all culprits.

Norm Faustino · Norm Faustino's Garage

Jack up the front end and check the running gear and suspension for any looseness or play that shouldn't be there. In my opinion, if you have a vibration that dampens out with speed it is usually worn components of the type mried mentioned. you could start cheap by changing the inner and outer wheel bearings and have the rotors checked for trueness. If you have a warped wheel or rotor you will see the steering wheel shimmy at all speeds above 15-20 mph or so. These are just general rules of thumb and guidance but with systematic approach and process of elimination you will find the problem. Good luck!

al lkosmal · 08:31 PM

I am/was in the same boat. Shimmy at 70...gone at 80. On my way home from work yesterday, I noticed that is got slightly worse.....and then it felt like I might have a tire going flat. Got in the garage and found that the right front had considerable play....................front outer wheel bearing is toast. I'd start checking there. Cheap fix!

regards,
Al

Update,
Replaced the right front, inner and outer bearings today...............went out for a test drive and the bad vibes are gone. Solid man! I'll do the left front tomorrow....

al

PS: I bought this car in San Diego and drove it home to the Seattle (1400 miles) area a couple of months ago...the wheel shimmy was the only issue I could find with it. I was headed to the shop to get my wheels balanced, but before I got around to it..............wheel bearing failure. Glad it happened close to home.

newms · 10-26-2013, 01:02 AM

Are you running any wheel spacers?

jason2guy · 10-26-2013, 02:00 AM

its the tires. trust me. ive been thru it a dozen times
i always start checking the bearings and all that stuff then i get new tires and all is well

Vereeken · 10-26-2013, 02:32 AM

I also suggest looking at wheel spacers if you have any.

The tire should be balanced with the wheel spacer included and should then go on in the same way.

KFC911 · 10-26-2013, 02:50 AM

Quote:

Originally Posted by jason2guy

its the tires. trust me. ive been thru it a dozen times
i always start checking the bearings and all that stuff then i get new tires and all is well

I'm with Jason...just because you got the tires rebalanced doesn't meant they're not still the culprit.

steve911T · 10-26-2013, 05:25 AM

Been there, done this. Check the front end and if nothing is bad, find someone who can balance the tire on the car. We are lucky in the DC/MD are having a company called Radial Tire in Silver Spring who can do this and it has always solved the problem. If the tires are really shot, uneven wear, etc. get new ones. Problem solved.

Alan Lindquist · 10-26-2013, 07:20 AM

We'd like to think that the tires were balanced correctly but it is possible that the balance was not done adequately. I had the same shimmy and went to a "nearby the office" shop and had the tires balanced. The guy said that they "matched" the tires to the rims by re-seating the bead to assure that they were "round" on the rim. Then they balanced them using much less compensating weights. I had the same problem.

I took it to another shop and asked them to check the balance. They came back laughing and said that the previous balance was done with inadequate weights applied. They fixed it using their approach (more weight in different spots) and the problem went away.

They were nice enough to not charge me and encouraged me to come back when it was time for tires and give them the business.

Bob Kontak · Bob Kontak's Garage

Quote:

Originally Posted by shuzboomer

Tell me where to start.

Put the front end on jack stands and grab the wheels and reef to side and top and bottom. If play is felt, get under the car and have a pal do the pulling until you spot the movement (slop) in the parts mentioned above.

Do this with the steering wheel unlocked and locked. May help you isolate.

Spin the wheels and feel for any resistance indicating bearings.

I am going out on a limb here, even though you said the vibration is felt directly through the steering wheel. If the whole car vibrates, there may be issues with the motor mounts. I am not sure of the symptoms with tired/exhausted 911 motor mounts but I have see a lot of bizarre vibe harmonics coming and going at different speeds with bad mounts on conventional cars. Of course, these cars have the engine in the front.

Jerome74911S · 10-26-2013, 08:10 AM

I am going through this and have a thread on it, too. Yesterday my shop rebalanced the front tires, because the shop owner felt that the young new guy in the shop might have gotten it wrong. Sure enough, with a lot fewer weights stuck on - although now in the correct places - the shaking in the steering wheel (at 60+ mph) is gone.

So, I zipped on up to 100 mph (160 kph) (I will not mention the country I was in) and at that speed I got a fierce, heavy vibration from the rear of the car. The left rear wheel bearing is a tiny bit loose; it is hard to imagine it causing this strong vibration, but who knows?

Bottom line is, start simple, but check everything and do not assume what it is. Be methodical.

jason2guy · 10-26-2013, 08:53 AM

The tire and wheel can balance and still cause vibration. Tires only last 15-20k on a 911
I just bought new tires yesterday and know im sitting at another shop getting them road force
balanced cause the shop that put them on didnt even know
how to work the balancer. I hate taking this car to a shop
its nerve racking

jason2guy · 10-26-2013, 08:54 AM

The tire and wheel can balance and still cause vibration. Tires only last 15-20k on a 911
I just bought new tires yesterday and know im sitting at another shop getting them road force
balanced cause the shop that put them on didnt even know
how to work the balancer. I hate taking this car to a shop
its nerve racking

jason2guy · 10-26-2013, 08:55 AM

The tire and wheel can balance and still cause vibration. Tires only last 15-20k on a 911
I just bought new tires yesterday and now im sitting at another shop getting them road force
balanced cause the shop that put them on didnt even know
how to work the balancer. I hate taking this car to a shop
its nerve racking

mreid · 10-26-2013, 09:00 AM

Okay, I heard ya the first time!

jason2guy · 10-26-2013, 09:57 AM

Sorry bout

CountD · 10-26-2013, 10:03 AM

Had the same problem - tried everything - ended up being a bent rim - ovalized - and no one picked this up after rebalancing, new tires, new ball joints, new shocks, etc. It was a stinking bent rim that could not be seen by the eye....at 70 mph...

gsxrken · gsxrken's Garage

Tires. They can be balanced every week but they seem to get cupped or chuffed up and you'll never get rid of it.
911s are the most sensitive car I've owned tire-wise. Borrow a set from another PCA or Pelican if you can to prove it

porsche930dude · porsche930dude's Garage

how old are the tires? swap out the fronts for spares and see if it goes away. check for looseness jacked up at the ball joint.