vjd3

My 95 C4 exhibited something interesting driving on the highway home this evening; the most horrible, high-pitched screeching sound, apparently from the rear of the car. Not drivetrain related, does it coasting in neutral, too.

My first thought was worn brale pads, as I know some have those little wires in them that are designed to screech when they are almost all the way down. But I don't have a brake pad wear light lit on the dash, and the car was always dealer serviced, as far as I know at least, so I'm assuming stock pads.

Secondly, the car will roll and drive silently in a straight line or while accepting steering input to the left; but even a little steering input right of center, much less a turn, and it's screech city.

Ideas? Car's under factory warranty. Wheels looked fine when I got it home; I'm sure my neighbors were thrilled to hear me coming down the street (curves to the right).

Vic
95 C4

PeanutinCA

Wheel bearings???? On one side????

Ray Calvo

I once had an Audi that was exhibiting a similar screeching, but largely all the time. Turned out to be a rock caught between the brake splash shield and the rotor. Might suggest pulling the wheel and push back a bit on the splash shield (might be hitting the rotor or there's debris between the shield and rotor; I would espeicially suspect it if it came on all of a sudden).

I don't think bad bearings make a high pitched squeal; not in my experience. I also haven't heard of differential or limited slip giving such noises either.

By the way; those dopey wires telling you that the pads are worn - they don't cause any screeching, but DO light up a light on the instrument panel. No way could those puny little things cause a major squeal on purpose.

Under warranty??? Why bother us; let the dealer screw with it!

tom_993

Vic,

Two of the points you mention seem to be in contradiction to each other. One, the noise seems to come from the rear and two, it only happens when steering to the right. Since steering doesn’t effect the rear wheels, why would left or right make a difference? If it were a rock, it would have to be in the front, as it only makes contact (and noise) when steering right. Puzzling. Try this: park the car with the wheels facing slightly to the right. Jack up each corner and rotate the wheel. See if you hear the screeching. If you do, trace it to the source. I’ve had stuck rocks before, and the screech was so loud it was obvious to me which corner it was in. Is this the case with you?

You didn’t mention what speeds (all?) this occurs at. Also, do you have a limited slip differential? There could be something inside it that’s broken, something that doesn’t come into play unless the left rear wheel is rotating faster than the right rear wheel. Come to think of it, I suppose this could be true of an open differential as well, although that seems less likely. To test this theory, you could try jacking up both rear wheels simultaneously and spinning each. Try spinning both together (this will take two people) and one at a time. This may or may not replicate the problem, as you won’t be able to spin the pinion (the input shaft of the diff), but it’s worth a try. Like Ray, I’ve never heard of a diff screeching, but there’s always a first time!

I don’t think it would be a wheel bearing, as it would screech all the time, not just when turning.

Keep us posted. I’d like to know what it turns out to be. If there’s any more data, let us know that as well.
Good Luck!

Tom
’95 993

vjd3

Tom:

The car is at the dealer now. My guess is it's the driver side rear wheel that is the source of the noise. I pulled the rim and saw no evidence of a rock or anything else. It was very difficult to turn the wheel at all with the gearbox in neutral and the e-brake off, not sure if that is normal or not as I've never tried before.

The car is a C4, so I don't think there is a limited slip beyond the AWD system.

I suppose that turning right would still change the load on the rear suspension, but I really have no experience. And it happened at all speeds, whether 70 on the highway or 10 on the street.

Naturally, once I got the car on the flatbed and down to the dealer, the noise went away. But they are checking it out and I will post what, if anything, they find. I suppose it could have been a piece of grit or something that dislodged when I pulled the rim

Vic
95 C4

tom_993

[quote]Originally posted by vjd3:
<strong>It was very difficult to turn the wheel at all with the gearbox in neutral and the e-brake off, not sure if that is normal or not as I've never tried before.
</strong><hr></blockquote>


This is not normal. You should be able to spin the rear wheel, even if the other wheel is still on the ground. I wonder if you have a stuck e-brake on the left rear? The e-brake pads have worn down and now they’re making metal to metal contact. Perhaps a right turn puts enough stress on the left rear to push the e-brake around a bit, causing the contact. Or, the right turn causes the left rear to speed up a bit (relative to the right rear), which again moves something in the e-brake to cause the contact. There could also have been a rock or other debris inside the e-brake and it fell out as you loaded the car on the flatbed. I assume you’re acquainted with Murphy?

There could also be some problem in the left rear half-shaft, but that seems a bit unlikely. The differential is also a potential, but less likely, suspect.

vjd3

It appears Mr. Murphy is at work ...

The dealership's master technician drove the car a couple of times, noted no unusual sounds, removed the rim, inspected the rotor, caliper, e-brake, hub ... said all looks fine.

Amazing what flatbed ride will do for a Porsche. Would it have cured a holed piston? ;-)

Vic
95 C4

E. J. - 993 Alumni

Did he take off the brake rotor too? 'Cause I don't know how to inspect the e-brake without doing that.

E. J.

vjd3

The service rep said he took everything apart; their first thought was that the ebrake had failed and was causing the screeching. He told me that a Porsche owner had the same complaint and when he brought the car in they discovered he had been driving with the emergency brake on the whole time. It was a new Boxster owner ;-)

On my way to pick up the car now. Can't wait to get out of the Dodge Neon they gave me, I can tell you that!

Vic
95 C4

jason952

I had a rock behind one of my rear rotors, I thought the thing was gonna blow up, awful, high-pitched LOUD noise anytime the car even budged.

Jason