Help - Do I Need an Alignment?

[guidob222]

Hello - I have a 1982 Porsche 911 SC...the car pulls to the right slightly at any speed; howeer, at high speeds over 65 MPH, the steering wheel shakes enough to rattle my wristwatch. Do I need an alignment? Wheel balance? The odd thing is It doesn't happen all of the time??? I do have aftermarket 17" wheels: 17x7-1/2 Fronts (205/50-17) and 17x8-1/2 Rears (255/40-17)...could it just be the lower profile tires pulling? Tires have about 23,000 miles...no sign of weird un-even wearing. I have owned the car for 5 years - never had an alignment done. Should I just go ahead and pay for an alignment/wheel balance for peace of mind? If so, how much should I expect to pay for this? Thanks so much for all of your help! Have a great holiday weekend!

[rallyracer]

Fix your shake, then check alignment. What tire are you using? 23k miles is probably enough to replace. Make sure you aren't on the tread bars.

1. Put the front of your car on jack stands, and check for worn parts. grab the wheel at 3 and 9 oclock and shake back and forth. Should be no movement in steering components. Shake at 12 and 6 oclock. Should be no movement in hub bearings. Spin the wheel. Brakes should not stick.

2. Check tire for slipped belts. run hands flat around tires to check for lumps. Visually check for spots with greater wear.

3. Take front wheels to a quality wheel balance shop. Spin balance check.

4. Some 911's responde poorly to the wrong wheel bolt hole being on the wrong wheel stud. Someone else can give you more info on this.

If it's really intermittent, you may have a sticking caliper. look for discolored rotors, possibly on right side. The more you drive, the more they heat, the worse the warp, the more the shake.
David

[mkossler]

Concerning the pull to the right:

You need to pay careful attention to whether the roads you commonly drive are crowned. This is commonly done to aid drainage, and will create a minor "pull" in any well-aligned car (unless it has positive caster off the charts).

I would also check the air pressure in your tires.

There is a condition called "radial pull" that can also occur for a number of reasons, and can begin to show immediately or after a considerable amount of wear.

Finally, inspect the wear on the tires, especially the fronts. If you see "cupping" along the edges of one or both tires, you have a toe-in or thrust angle (rear-to-front) condition that needs to be addressed. If you have smooth, even wear along the outside edges of both tires, alignment is not a likely culprit. Regardless, if you haven't had an alignment done in the recent (1-2year) past, I'd recommend you get one. They're not expensive, and the right shop will give you a very accurate report of the state of your wheel alignment at all four corners.

Now the Vibration:

The vibration, as you describe it, is not likely due to lateral or radial run-out ("belt shifts" some call it). The primary indicator of run-out will be a slow back-and-forth movement in the steering wheel at slow speeds, and increasing vibration as speed increases. You did not describe this.

I would look for:

-Out of balance condition. This is indicated by a noticeable build-up of vibration as you approach a certain speed, and some fading of vibration once you are past it. The build-up and decrease generally happens over a 10 MPH range. This would be the most likely culprit to me. Tires are made of a variety of compounds, and the Banbury mixers generally used to combine materials before they are extruded don't always produce a homogeneous mixture. This translates to uneven density in the tire compounds, and thus uneven wear down the road.

-Foreign matter caught in the wheel, perhaps on the inside. Mud especially can be an issue, and will not always be removed by a car wash (Shame on you if you're using a car wash on your 911 anyway! ).

- A negative caster condition. Very rare, but negative caster will produce intermittent vibration at speed.

All of these conditions can be checked and addressed at a competent tire and wheel center. Good luck!

Matty K.

[Miguel Antonett]

Yes, I would check the tire balance and alignmnet, mainly if it has not been done in 5 years.

[old man neri]

Another thought....

You said you had after market rims. Is the bore size of those rims the same as the hub on your car? In some cases hubcentric rings are required. Without them there is the possibility of the rim not being perfectly centered and this condition manifests itself as higher speed vibration.