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Macht Schnell
 
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Rear End Howl

Hi,
I have a Howl in the rear of the car somewhere and am trying ti find it. I wiggled a wheel today and thought the bearings felt loose to me. I have this howl that gets real loud at 2000-2500. It continues from 2500 but as you go faster and everything gets noisier it is not as noticeable and changes to a higher pitch. It is real bad from 2100-2500. I wold think it is a wheel bearing, except that when you engega the clutch while running down the road at 70mph, the sound disappears completely. If it was a wheel bearing, I would think it would keep singing. Any ideas?

Thanx!
Les
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Old 01-08-2008, 05:09 PM
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When my rear bearings went south it went from whining/howling to humming/throbbing to a loud clunking noise. It changed around at will.

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Old 01-08-2008, 06:45 PM
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Macht Schnell
 
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I was wondering if bearings can go silent when you engage the clutch?

Les
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Old 01-08-2008, 06:57 PM
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Mine didn't go silent when pressing the clutch every time. They went silent when they chose to do so. If yours stops when the clutch is pressed I would say it's not the wheel bearings.
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Old 01-08-2008, 07:11 PM
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Yeah, it was explained to me that a wheel bearing makes a howling noise.
Old 01-08-2008, 07:47 PM
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Possibly while in gear appliying load to the bearing would cause the howl. Then when you let the clutch out the car would coast removing bearing load eliminating the noise temporarily. I'm sure in time the noise would eventually come back but much greater amounts as well as more damage. More than likely but then again just a thought.
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Old 01-08-2008, 07:55 PM
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Les, I had a right rear bearing going out.

It starts off with a very light high pitch hum, then progresses to the point where you think a Apache Helicopter is following you at various speeds.

In itís later stages, the sound is more prevalent during cornering.
But since it is progressive, you will not really detect it until your daughter rides in the car and asks why the radio is so loud
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Old 01-08-2008, 08:04 PM
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Could it be somthing as easy as a loose fanbelt?
Old 01-08-2008, 08:05 PM
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Quote:
Originally Posted by GJF View Post
Possibly while in gear appliying load to the bearing would cause the howl. Then when you let the clutch out the car would coast removing bearing load eliminating the noise temporarily. I'm sure in time the noise would eventually come back but much greater amounts as well as more damage. More than likely but then again just a thought.
I thought about that too, and got on and off the gas to see if it changed with varying load, but it didn't. I'm not sure that you can truly vary the load much at 70mph though.

Les
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Old 01-08-2008, 08:10 PM
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Quote:
Originally Posted by snbush67 View Post
Could it be somthing as easy as a loose fanbelt?

Hmmm,
I've never heard a loose fanbelt on a Porsche, but this sure sounds like a bearing. I don't hear it free revving it. I also think it's speed related not rpm necessarily. I'll check this tomorrow.

Les
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Old 01-08-2008, 08:12 PM
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Other items to consider is the throw out bearing or the input shaft bearing. Just guessing, I'd rather it be a wheel bearing than to other two.
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Old 01-08-2008, 08:20 PM
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Quote:
Originally Posted by GJF View Post
Other items to consider is the throw out bearing or the input shaft bearing. Just guessing, I'd rather it be a wheel bearing than to other two.

Hi,
Yeah, I've considered all those also. Everything is new except the wheel bearings. That doesn't mean that I couldn't have problems with them though. The input bearing and throw out bearing have maybe 1000 miles or less.

Les
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Old 01-08-2008, 08:39 PM
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Les,
I think that the release bearing will show itself to be bad at any RPM and any speed. If you apply any pressure on the bearing at all and the noise goes away, then the bearing is potentially bad. On the other hand, if the release bearing is totally shot, it will grind when pressure is applied.

I don't believe the wheel bearing is the culprit. You seem to have eliminated that with your on-throttle off-throttle test. Most of the load on the wheel bearing at cruising speed is from gravity, and the weight of the car, not the torque of the engine. Since the noise goes away by disengaging the clutch, I would say that the problem will be found elsewhere.

My guess (albiet amateur) is that the problem lies between the mechanisms you are affecting when you engage and disengage the clutch: clutch disc, flywheel, and input shaft of the tranny.

I think you have all but eliminated the flywheel because you said the noise doesn't show itself when you free rev. A loose flywheel will vibrate while free revving, and will quit vibrating when you hold in on the clutch because you are effectively pushing the flywheel into place with your foot. A bent or out of balance flywheel will always vibrate at a certain RPM regardless of whether the clutch is engaged or not.

The clutch disc itself doesn't seem to be it either. The disc is clamped in place while cruising, and is somewhat free spinning when disengaged. When clamped in place, it is part of the flywheel (so-to-speak), and can't make noise on it's own.

That leads me to suspect an internal tranny problem.

Once again, I am a rank amateur, and believe me there are far more senarios that could explain your dillemma. I only hope I am wrong, and that the real experts chime in and shoot big holes in my theories.

Good luck with it!

Drew
Old 01-09-2008, 07:02 AM
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Quote:
Originally Posted by Wolf300tt View Post
Les,
I think that the release bearing will show itself to be bad at any RPM and any speed. If you apply any pressure on the bearing at all and the noise goes away, then the bearing is potentially bad. On the other hand, if the release bearing is totally shot, it will grind when pressure is applied.

I don't believe the wheel bearing is the culprit. You seem to have eliminated that with your on-throttle off-throttle test. Most of the load on the wheel bearing at cruising speed is from gravity, and the weight of the car, not the torque of the engine. Since the noise goes away by disengaging the clutch, I would say that the problem will be found elsewhere.

My guess (albiet amateur) is that the problem lies between the mechanisms you are affecting when you engage and disengage the clutch: clutch disc, flywheel, and input shaft of the tranny.

I think you have all but eliminated the flywheel because you said the noise doesn't show itself when you free rev. A loose flywheel will vibrate while free revving, and will quit vibrating when you hold in on the clutch because you are effectively pushing the flywheel into place with your foot. A bent or out of balance flywheel will always vibrate at a certain RPM regardless of whether the clutch is engaged or not.

The clutch disc itself doesn't seem to be it either. The disc is clamped in place while cruising, and is somewhat free spinning when disengaged. When clamped in place, it is part of the flywheel (so-to-speak), and can't make noise on it's own.

That leads me to suspect an internal tranny problem.

Once again, I am a rank amateur, and believe me there are far more senarios that could explain your dillemma. I only hope I am wrong, and that the real experts chime in and shoot big holes in my theories.

Good luck with it!

Drew
I've been "hoping" it was wheel bearings. I had the tranny done also and it has only about 600 miles on it. But you know how that goes.

Les
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Old 01-09-2008, 10:13 AM
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It could even be the CV's.
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Old 01-09-2008, 12:18 PM
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Quote:
Originally Posted by les_garten View Post
Hi,
I have a Howl in the rear of the car somewhere and am trying ti find it. I wiggled a wheel today and thought the bearings felt loose to me. I have this howl that gets real loud at 2000-2500. It continues from 2500 but as you go faster and everything gets noisier it is not as noticeable and changes to a higher pitch. It is real bad from 2100-2500. I wold think it is a wheel bearing, except that when you engega the clutch while running down the road at 70mph, the sound disappears completely. If it was a wheel bearing, I would think it would keep singing. Any ideas?

Thanx!
Les
My guess is the Ring and Pinion. Does the pitch change when in accel or decel at those RPM's and gear selection you mention?
A loose wheel bearing will also generate a groaning kind of noise when the brakes are applied with moderate pressure at highway speeds.
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Old 01-09-2008, 12:25 PM
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Quote:
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It could even be the CV's.
I had the CV's greased at the same time as everything else.

Les
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Old 01-09-2008, 02:53 PM
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Quote:
Originally Posted by WERK-I View Post
My guess is the Ring and Pinion. Does the pitch change when in accel or decel at those RPM's and gear selection you mention?
A loose wheel bearing will also generate a groaning kind of noise when the brakes are applied with moderate pressure at highway speeds.
There is no change with brake application, and it is the same at 2500 in 3rd or 4th gear. The only pitch change I can achieve is engaging the clutch, it goes away when the clutch is engaged.

Les
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Old 01-09-2008, 02:55 PM
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Quote:
Originally Posted by les_garten View Post
There is no change with brake application, and it is the same at 2500 in 3rd or 4th gear. The only pitch change I can achieve is engaging the clutch, it goes away when the clutch is engaged.

Les
When you say "engaged" do you mean your foot is on or off the pedal?
Old 01-09-2008, 04:14 PM
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Quote:
Originally Posted by Wolf300tt View Post
When you say "engaged" do you mean your foot is on or off the pedal?

Engaged to me is my foot is holding the Clutch down, foot to the floor.

Les
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Old 01-09-2008, 05:30 PM
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