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Old 09-01-2010, 10:01 AM   #1
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Need help with vibrations

Hey all,

I know cars well but I don't yet know the boxster's weak points well, or what are known to cause rotation-related vibrations.

I'm running a set of 18x8/18x10 Porsche wheels with near-new Michelin Pilot Sports (NOT PS2s). I can confirm that when they first went on, their balance was superb.

After driving the car about 1000 miles, I've got vibration issues at a variety of speeds and situations. At around 45mph the wheel shakes, then evens out with some minor vibrations above and below it. 80+ starts to get really bad. Around 70 it gets twitchy weird. 75 is baby smooth. 65 is smooth.

There is no notable bends in the wheels. I have a set of winter tires I'm going to rotate on to see if it smooths it out, which would show me that it's balance or tire related.

If not, are there any known issues with the boxster suspension/control arms/links/bushings that could cause something like this?

If it is the tires, I'm going to get them road force balanced at a local shop.

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Old 09-01-2010, 10:23 AM   #2
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Maybe alignment, front, rear or both.

There really is no mileage component to an alignment.

Leave the alignment shop, hit a curb or a pothole, and you may need to head straight back in.

For lots of reasons (Range, handling, etc.) suspension components are often much lighter and less robust than in the past, and roads are generally much worse as well. This means that they are less able to withstand the many road hazards and still maintain proper alignment settings.

How many curbs, speedbumps, expansion joints, potholes, etc. might you have encountered in your 1000 miles?

Alignment could easily be the culprit here.

Cheers!
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Old 09-01-2010, 11:05 AM   #3
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I have had the same issue for 3+ years. I have tried all sorts of wheels, rotated balanced and changed tires, replaced disk rotors, bearings..... the list goes on.

the only this left is to check or replace control arms or bushings. I cant imagine that after replaceing eveything that rotates this problem will not go away.

one thing I have noticed, that the shaking comes and goes, at speeds over 50mph. I cant see where a tire or rim can be out of balance one day then back in , and back out. When it happens it is a rythmic situation depending on speed. At 75mph, it shakes hard for 7 sec, smooth for 4 sec, and shakes hard again for 7.
way too weird.

This has stumped all that has tried to fix it. Anyone have suggestions for us?
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Old 09-01-2010, 11:14 AM   #4
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Jhandy - I think that's a really good description of some of the symptoms I experience, where I can't always consistently reproduce the imbalance at a given speed. The only times it ALWAYS appears it at 81+ mph.

Otherwise, I've seen it migrate around 45mph on and off.

I'm going to rotate to my winter tire setup. If it cures it or it changes significantly, then it's definitely tire/wheel related and I can at least narrow it down to there.

If not, then I'm going to suspect a worn out bushing or wheel bearing allowing too much slop. The wheel bearings themselves make no discernable noise, so I'm disinclined to think it's wheel bearings. Alignments can cause imbalances, but rarely ones that wander in and out of vibration. Still a possibility though.

Worn out control arm bushings or bent control arms can cause all sorts of issues.

One thing I will always remember though is that lightweight, short-wheelbase cars with rigid bushings and suspensions setup for instant response....

Well, those cars tend to magnify even the slightest issues. So a hairline crack in a bushing or imbalance somewhere will magnify alot more than it would elsewhere.
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Old 09-01-2010, 12:50 PM   #5
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Mine begins at 70mph. Viibration appears to be from the rear passenger wheel. Sometimes it is smooth through 80, but 75% of the time I'll have some vibration. I had that wheel balanced but still seems to reoccur.

I can't replicate the issue though. Turning to left, turning to right keeping the weight on either side, doesn't alleviate the virbation chatter. Decelerating keeping the weight up front at those speeds, still chatter. Hammering the throttle to keep the weight in the rear, still chatter over 70mph.

The 3 wheel weights are the strips that reside just inside the spoke (adhesive wheel weights). The 4th wheel (rear passenger) was missing this weight when I picked up the car. I took it to get balanced and they placed a crimper style weight on the inner edge of the rim, not an adhesive strip on the inside. I can only think this is the cause of my issue.

Thoughts???

Edit: Realized that in the time I've spend mulling this over, I could just get it done. So I found a place that will replace these, I'm just getting it done this evening to stop speculating on this variable.
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Old 09-01-2010, 01:01 PM   #6
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Don't forget to check the wheels themselves, they have been known to get bent. When I bought my Boxster, the dealer had taken the sport classic wheels off to give to another customer, low and behold the turbo twists I received needed two wheels to be replaced, what a dumb dealer....
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Old 09-01-2010, 03:17 PM   #7
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The on and off and on thing is so strange that It has to be indicitve of a certin problem.

Some days it does not do it at all at any speed.

the only thing left to replace is the steering rack. is there something in the rack or steering box that could cause this?
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Old 09-01-2010, 03:39 PM   #8
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I have 18s on mine with Falken 912's. The ride is smooth as can be. Perfect tire for Florida.
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Old 09-01-2010, 10:07 PM   #9
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Update: I got the 1 known culprit tire balanced, 2 adhesive weights laid inside the wheel. Pushed it to 70mph and still some chatter but not from back there and the car felt better, not by too much though.

I returned, got the other 3 wheels balanced. Pushed car to 70mph felt great. Took the car back out tonight (after traffic was gone) and pushed the car to ...ahem... very fast... and no chatter! no vibrations whatsoever. For some reason these wheels weren't balanced well at all. The shop owner said BF Goodrichs can be hit or miss and sometimes they wear weird and fall out of balance. So whatever that is worth. He did fix the previous shop's dumb mistake though and got the car perfect.

All this for a measly $10/wheel. Wow. +1 for Austin Tire Man on Manchaca.
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Old 09-01-2010, 11:33 PM   #10
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Well realize that it's natural for a tire to come out of balance as it wears. They also usually get out of round as well.

You really should have the tires/wheels balanced several times throughout their lifespan for optimum ride.

Cheers!
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Old 09-02-2010, 06:02 AM   #11
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Sounds like they didn't clean the area for the weight at all. Inside Porsche rims get pretty dusty. I would have them rebalanced after 5K.

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