Bad Vibrations

[RandallNeighbour]

Hey, I did have one question for all you fellow boxster owners. I am now 1/3 of the way through my vacation, driving from Houston, TX to Northern CA and back.

I've had HOURS to ponder why the rear of my car vibrates a lot from time to time, then is smooth as silk like I was driving on glass. Same goes for the front end. It either shivers like I have a bent rim, a bad tire, etc. Some times the steering wheel shakes, and some times it's nice and steady. All this happens while it's set on various speeds on cruise control. So speed is not the issue here (ie, vibrations come and go at 65, 70, 75, 80, and 85).

Just to clarify, I can be driving along on seemingly smooth black top on cruise control and the shimmer begins, then fades to nothing, then comes back, etc. I am at the same speed when this happens.

Before I left, I had a four wheel alignment done as well as road force balancing on all the tires. But, this problem has been in existence since I bought the car a year ago. I just can't seem to fix the problem. Replaced the tires, had them balanced four times, had it aligned four times too. Grrrr.

If this were a bad tire, a bent rim, a tire out of balance, it would be a consistent issue at certain speeds, right? Am I just feeling crappy pavement below my butt or can someone tell me what's wrong with my boxster so I can have it looked at when I get into LA?

[rctboxsters]

Randall,

I do not know what's wrong with your car but I think you will enjoy the drive. I drove back to No. Cal from Arlington several years ago. Almost one full day of continuous driving. It was a new experience for me driving through several states under the hot sun, with no AC. Hey, it was an old MX6. Anyway, have fun!

Richard

[ranbar2]

I experience the same phenomemon. Some drives it's smooth as glass, others the steering wheel shakes like it has advanced Parkinsons. I have had it checked out several times by both the dearlership and the local indie porsche shop and the car is mechanically fit. What is really stange is that I can never predict when it will happen...two drives on the same day can be entirely different.

[deliriousga]

In the steering wheel or the seat? Is it a "vibration" or a "shaking"? What about RPMs?

There's an issue in the 3000-3300 RPM range with the dual-mass flywheel that's standard on the Boxster. I feel it all the time, mostly in the seat. Mine started a few months ago. The problem is similar to a warped rotor, but since the flywheel moves so much faster it's a vibration you feel rather than a shaking like you would get from a brake rotor. The range widens over time and mileage.

Here's what to look for: See if you feel it more when the RPMs are coming down through the 3000-3300 range. You usually don't feel it on the way up because you're going through the range so fast as you accelerate through the gears. As soon as you feel it, hit the clutch and see if it goes away immediately. If it does, it's most likely in the drive train.

Since the Boxster has a dual mass flywheel, I have been told it can't be machined so it must be replaced. The flywheel for the Boxster is $700 for just the part. To fix it, I will be replacing my flywheel when I do the clutch in a few months with a lightweight aftermarket "racing" flywheel with inserts. Then as the flywheel wears down I can just replace the insert for way less money. That and the lighter weight flywheel will give me more rwhp since it takes less power for the engine to get the flywheel spinning.

[RandallNeighbour]

John, I had hours and hours on the road to look for what you are talking about with the 3000 to 3300 rpm vibration issues. I do not think this is the problem.

I believe it's wheel related. Worn rubber doesn't help it either.

I'm gonna save up and buy new rims and tires. I really want 18 inch Carrera lights, but I hear the 97's can't support them (bearings go out) although I can guarantee they are lighter than my 17 inch ROH's... which belong on a Trans Am, not a Porsche.

[deliriousga]

Originally Posted by RandallNeighbour

John, I had hours and hours on the road to look for what you are talking about with the 3000 to 3300 rpm vibration issues. I do not think this is the problem.

That's good news. It's not a cheap fix.
Just blowing through ideas so ignore any you think are a little off from what you've been experiencing on your trip.

Have you ever cleaned your ABS sensors? They are magnetic so they can have metallic brake dust stick to them and eventually not "feel" the wheel moving. My 928 did that and caused major vibration at speed. They should be cleaned at every brake change.

How many miles do you have on her? If high mileage, wheel bearing issue?

Have you ever used "fix-a-flat" or the like in any of the tires?

Have you had any of the tires plugged?

Do you have metal Porsche crested caps? (This one can get you if the guys take the caps off, check the pressure and balance them, then put the caps back on since they are heavy caps.)

Bad/worn shock or spring?

Pressure correct in all of the tires? Everyone who has balanced the Boxster has filled them to the standard 32/32 psi instead of the Porsche recommended 29
Front/36 Rear.

Loose undercarriage cover or front bumper?

I know it's a lot of stuff to consider, but there are so many things that can cause vibration. Hope you find it soon!

[RandallNeighbour]

Lots of good things to look at! Thanks. I'll let you know what I discover.