Luca Signore

Hi! I have a 2002 Porsche Boxster S that has been experiencing a few weird problems that two shops have been unable to fully diagnose, but that I am still feeling, and I was wondering if you guys had any ideas about the cause of the issue before I bring it to another shop.

I do remember being forced to exit a parking lot a couple days before I started noticing it on a dirt road that had a few bad pot holes - not sure if this has anything to do with it, but I drove it back from that place (about an hour in the hills - pushing it), to the grocery story the next day, and to work (25 miles) the day after that and it felt completely normal. I only started feeling it on my way home from work that day.

The symptoms I can notice are:
A strange vibration/rapid bumping noise coming from the car. I'm pretty sure it's coming from one of the front wheels, but I cannot exactly place it. It's very subtle, but it feels like the car isn't riding the way it should. It almost feels like one of the wheels is wandering slightly on the road, but the car doesn't really pull to either side. Maybe slightly to the right, but not really noticeable unless I fully let go of the wheel and still accelerate. It kind of feels like the wheel isn't completely round or something, but I just had the tires replaced and balanced.

The first shop I took it to said the motor mount looks fine and that the shocks look fine too - the rear passenger shock is leaking slightly, but they did not recommend replacing it.

The second shop said that my tires were worn and that the wheels needed to be balanced - I got new tires (Conti Extreme Contact) from them and they balanced them on a Hunter Road Force machine, and while the car does feel slightly better, I can still feel the vibration/clicking through the steering wheel. I emailed them saying the problem was still there and they said that they didn't want to waste my money and didn't recommend getting an alignment until I get new shocks. He said the vibration could be caused by steering bushings, tie rod ends, or the shocks, but said he wasn't positive.

Any ideas?

dr914

with new front tires and a new balance, if the problem is still there but slighter, maybe you have a bent wheel. Alignment would not cause that vibration. How many miles on your car?
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Luca Signore

What would be the best way to check if the wheel is bent? The car just hit 85k miles this morning.

Macster

Tech should have *eyeballed* the wheels/tires for any signs of excessive run out.

To check for bent wheels you might be able to with the car in the air and the tires off the ground have someone turn the wheel/tire by hand while you sight along the wheel rim at where the tire bead fits/seals and check for any run out. (Turning the rear wheels might be a bit of work.)

Unless you have confidence in your ability to do this (as an ex-machinist I have the ability -- at least I used to and I might still have it -- to spot just a few thousandths of an inch of runout from like almost a mile away but not everyone has this ability) you might want to have the car at a shop lifted up and the tech use some kind of dial indicator against the wheel to check for run out. Axial run out can be checked with the tire mounted but radial runout should be checked *before* the tire is mounted for this wants to see if where the tire mounts the runout is within limits. But maybe the tech has a work around or a good eyeball.

dr914

we call the tire mounting guys, tire "monkeys" because they do not pay very careful attention to their job, repeating the same procedure over and over again without thought. It is simple when the wheel is on the balancer, to put the pointer against the rim and slowly rotate the wheel to make sure that the runout is true (not going in and out or up and down. Once that is ascertained, they can mount and balance the tire, and carefully put the wheel back on torquing the bolts to 90 or so ftlbs and in a criss cross pattern. Then finally spinning the wheel to again make sure wheel and tire spin true

Luca Signore

Hey guys

Quick update: I took the car to a wheel/tire shop this weekend and they took the car on a test drive, said the front wheels were .5 oz out of balance, but that they could not feel the vibration/judder I was talking about. I'm getting really frustrated since none of the people I have taken the car to can feel what I'm feeling, but it's definitely there. It basically feels like the car is way too stiff and it's causing a constant harsh judder/vibration, but it's very subtle.

Any other ideas? I know my shocks are close to being blown, but could that really cause it? Would tie rods possibly be the issue? At this point I'm considering getting an alignment since it's cheap enough, but I'm unsure that it would actually address the problem I'm feeling.

Thanks again.

Macster

Not clear to me if the car has been on your position a while or you just picked it up.

If the car is relatively new to you these cars have a very communicative steering and suspension. To someone used to the near total isolation from the road a number of other cars have this can be an unfamiliar experience.

The tires tend to tramline a bit and when/where they do this is mainly tied to the road surface. In the bay area some roads, heavily traveled roads -- and almost all of them are heavily traveled -- develop depressions where the vehicle tires run. On the freeways the right most lanes really suffer from this. More than once in either of my cars this tramlining got so bad I thought I have a low tire and pulled off the road to check. And I travel these roads daily.

You mention you got new tires fitted. It take some few mles -- hundred or two -- for the new tires to kind of settle in. Until this happens they can feel a bit strange.

How did the old tires look? Was the wear across the front and rear tire tread faces even? If the front or rear tires had even wear between tires or uneven wear across the tread faces this is a pretty good sign alignment is needed.

I believe the new tires you had fitted are not N-rated tires. I know many dismiss this N-rated tire business as just nonsense but the N-rated tires have all the characteristics Porsche deems necessary for tires suitable for use on its cars. Non N-rated tires don't have the load rating, the sidewall stiffness, that Porsche tires need. As a result the car can feel squirrelly. It is impossible for me to say that this is the case in your case but you should be aware thee behavior you feel may be due to the wrong tires being fittied.

But let's assume for now that is not the cause of what you are reporting. With some miles on the new tires feel the tread blocks. If you feel any indication of feathering, cupping, severe abrasion taking place this is a sign of a bad alignment. You would be advised then in this case to get a proper alignment.

If you take the car in for an alignment be sure you chose a place that knows how to properly align your car. I know of one indy shop down in your "area", Custom Alignment in Mountain View, CA.

2599 Wyandotte St, Unit A, Mountain View, Ca 94043, Mountain View, CA 94043, (650) 961-5311

There is also a Porsche dealer in Santa Clara on Stevens Creek Blvd.

Speak to the shop about what you are experiencing and ask the tech advise you on the car's suspension condition. Suspension hardware, incliuding shocks, have a limited service life. Often the life is long but it doesn't have to be. The tech will check for wear/play, bent/damaged suspension hardware, evaluate the shocks perhaps -- my Porsche tech sources tell me as long as the shock isn't leaking it is good and mine have stayed fluid tight for over 315K miles -- but let the tech tell you what he finds.

Luca Signore

Macster -

Thank you so much - this is awesome information.

The car has 85k miles, I bought it about 11 months ago at 79,5xx miles. I have driven it quite a bit, mostly commuting, but also a fair bit of hill twisties (Hwy 9, Tunitas Creek, Page Mill). I definitely felt a difference the way the car felt on the road when I got into it that afternoon.

The old tires were dry cracked (installed in 2011 by previous owner) and some Chinese crap tire. Yet, they handled pretty well and the vibration started on that tire. They did not seem cupped, but again the vibration started near the end of the life of these tires, and I got them replaced within 500 miles of the issue starting. The vibration/juddering is the same on the new tires. I have about 100 miles on the new tires so far.

I've taken the car to Sportech in Campbell and BRRacing in Los Gatos, both reputable shops, but neither has said that they can feel what I'm feeling. Driving it every day though, I can definitely notice the difference between how it felt before and how it feels now.

The alignment shop is a good idea - I'll call that one you mentioned since I've heard some horror stories of the repair costs and inspection costs from the Porsche dealer. I did a visual inspection myself of the car when I took the front wheel off this weekend, and nothing seemed obviously damaged or broken, but then again, I don't have a very well trained eye. When I bought the car, I got a PPI from a Porsche shop in the North San Jose area (can't remember the name right now) and they did mention that the rear passenger shock was leaking a bit, but I drove the car close to 6k miles with it like that and never noticed what I'm feeling now. It could be this, but it seems weird to me that the issue developed all once instead of gradually.

I have also noticed the steering feeling a bit number on center - I can turn the wheel an inch or so both directions without direct movement, which was not the case beforehand. It has also been a bit jerky shifting - which would indicate the engine mount, but the guys at Sportech said that the mount look good. Although, they also only charged me for half an hour of labor to inspect it, and they said that they didn't feel the vibration, so I don't know if they actually pulled the mount off the car to inspect it. Tie rods and the mount are relatively cheap and easy to replace, so I might do those myself and then get an alignment, but I also don't want to waste time and money replacing stuff that doesn't need to be replaced.

Macster

My experience with N-rated tires -- and I would not be surprised if this is also the case for non N-rated tires -- is after a while after they wear some they can go out of balance. The SA/techs where I take my cars say this is common. As the tire wears heavier areas in the tread wear away and a mild out of balance condition can occur. Often when I replace the worn out rear tires while the fronts have more than sufficient tread to go another 20K miles I have these rebalanced.

If the rear shock is leaking it will be ok for a while then it will not be ok. There is some margin of fluid but once that margin is used up/leaked out in this case, the shock will no longer dampen. What can then happen -- I spot this once in a while observing other vehicles -- is the tire/wheel will go up and down like it is going over a line of railroad ties. The shock can no longer control the wheel/tire assembly and its spring.

Before you get the car's alignment checked, look into replacing at least the leaking shock and its sibling on the other side to keep the dampening even at least on that axle. Have the shocks replaced *before* you align the car.

Regarding alignment: The factory manual says the car should be empty of any extra weight. The spare tire/tool kit should be present and stowed correctly. The tires should be properly inflated.The fuel tank should be full. Some places make a big deal out of putting ballast on the driver side floor/seat to align the car as it will sit on the road with the driver present. Both of my cars have been aligned with and without the ballast. I can't tell the difference. Also, when carrying an up to 200lb passenger -- coworker -- the car doesn't seem to be affected. Up to the shop and you how you want to go with this ballast business.

Also, be sure you specifically ask the steering wheel be "centered".

A bit numb on center... I really don't recall this in either of my cars. The car is still a relatively unknown to you. It could be some of the suspension/steering connections are worn out. It happens. Before the alignment you need to have the car checked for any signs of loose/worn/damaged/bent suspension/steering hardware and have this addressed *before* the car is aligned.

What else...? Oh, with cars equipped with manual transmissions it is imperative the brake and *clutch* fluid be flushed/bled every two years. I learned that even letting this go a bit over 2.5 years affected the clutch's action and performance and this affected shifting. After having the brake/clutch fluid flushed/bled the clutch action was once again smooth and shifting of the 5-speed likewise smooth.

Might mention as near as I could tell braking before and after the flush/bleed was unchanged. Braking was ok before and after. Still the change/improvement in the clutch action and shifting was worth the price of admission.

dr914

If there is play in your steering, you definitely have a problem. Surprised that the tire shops did not pick that up when working on your wheels and tires. USUALLY play in the steering is a bad tie rod end. Thing to do is to slightly move the steering wheel side to side within the range of the play, and have someone underneath observe where the movement stops, and that is what is loose or worn. If you have a bad tie rod end it would definitely cause vibration in the steering wheel