Intermediate shaft noise question

[K24madness]

It looks like the intermediate shaft is the source of my noise. Looks like the motor has to come out again I kick myself for not splitting the cases but at 29k miles who else would have? Some mechanics say don't worry about it. To me it sounds worry some. I will have the oil checked for metal just in case. Is this a time bomb or just annoying?

1996 993 with 29k miles.

[Steve@Rennsport]

JMHO, but at 29K, its rare to have an intermediate shaft problem. A real sharp, experienced mechanic can spot this with a stethoscope.

These things do occur, albeit rarely, so you'll need to open everything up to have a look.

[K24madness]

Originally Posted by Steve@Rennsport

JMHO, but at 29K, its rare to have an intermediate shaft problem. A real sharp, experienced mechanic can spot this with a stethoscope.

These things do occur, albeit rarely, so you'll need to open everything up to have a look.

I would tend to agree. Some of the low mileage 996tt guys have suffered the same fate so its not unprecedented.

[johnman001]

Please excuse my ignorance, but for the benefit of us uninformed masses, what does this sound like?

[Steve@Rennsport]

Hi John,

As you might imagine, such things are virtually impossible to describe in writing since many engine noises vary by frequency, pitch & amplitude.

Intermediate shaft noise sometimes makes a light knocking or rumbling sound that differs from bearing noises or wrist pin knocks. Its FAR easier for one to listen to various engine sounds under the tutelage of an experienced person to learn and discern the differences.

[johnman001]

Originally Posted by Steve@Rennsport

Hi John,

As you might imagine, such things are virtually impossible to describe in writing since many engine noises vary by frequency, pitch & amplitude.

Intermediate shaft noise sometimes makes a light knocking or rumbling sound that differs from bearing noises or wrist pin knocks. Its FAR easier for one to listen to various engine sounds under the tutelage of an experienced person to learn and discern the differences.

I understand the difficulty in description of sounds, and thanks for trying. I also understand the benefit of learning firs hand and in person from an experienced person, but currently none are available.

Do you know what typically makes noises when it is suspected that the intermediate shaft is causing the noise(s). Is it bearing related? Does the shaft walk axially and tap on something?

The reason I ask is that I had a noise that I could not identify in one of my spare engines. I have yet to take it apart. I was assuming it was a quiet noisy rod bearing but didn't really act like it was.

One of these days, the noisy engine case will be split and I (hopefully) will be able to identify the source of the noise.

[Steve@Rennsport]

Intermediate shaft noises stem mainly from worn bearings and worn (or mismatched) gears. Chain sprockets rarely make discernable noise, even when the teeth show some wear.

In some situations, excess end play (thrust) makes noise and thats caused by worn thrust bearings or an engine case that wasn't machined properly.

You'll know when you have it all apart.

While I don't recommend them for street cars, there are straight-cut intermediate shaft gears that eliminate thrust wear, however they do make a racket.

[K24madness]

I just came from the dealer. The tech feels it is coming from the intermediate shaft area. He is also hearing the noise in the bell housing. He felt the noise was traveling down the crank and that is why he also hears it in the bell housing area.

After taking him for a ride and having him listen to the noise inside the car he was not so sure it was not coming from the trans and traveling down to the intermediate shaft area. I don't understand how that can be since when the clutch is pushed in and the car stopped the trans does not turn.

When I go for a long ride the noise seemed to be less.

Couple more pieces to the puzzle. When I got the car the tune was so bad it barley idled and lumped around like a V8 chevy with cams at 600RPM. Did that hurt something? I also know the trans main shaft is bent.

I have a call into Jerry Woods. He has LOTS of experence so I hope he can provide some insight. His shop is not that far away.

[AlfonsoR]

How common is this problem? I have read some engine rebuild posts where people suggest that once your engine hits 100k miles, that is "not uncommon". However, I have also read a couple of high mileage posts where people put over 200k miles on their SCs or Carreras with nary an issue, which would suggest that the issue is not common. So what causes the problem repeated high reving, or poor lubrication???

I have only had my car for a month (got it at 98k miles) and will be doing the second oil change shortly at 100k miles, and will be doing an oil analysis. If copper shows high, it will give me some sleepless nights. I'll be wondering the same thing, "how long can I safely run it ?"

[Steve@Rennsport]

Originally Posted by AlfonsoR

How common is this problem? I have read some engine rebuild posts where people suggest that once your engine hits 100k miles, that is "not uncommon". However, I have also read a couple of high mileage posts where people put over 200k miles on their SCs or Carreras with nary an issue, which would suggest that the issue is not common. So what causes the problem repeated high reving, or poor lubrication???

Its not common on the air-cooled engines. Its a whole 'nuther thing on the water-cooled ones.

There are MANY factors that affect intermediate shaft bearing wear that include, but not limited to: oil change frequency, type of oil, and valve spring pressures.

I don't believe that high revs affects this unless one has stiff racing valve springs. These are not all the same since seat pressures vary among them and some are much worse than others.

[HawgRyder]

Don't forget to check the Pilot bearing too.
Because it is in the end of the crank, even in Neutral, clutch out, stopped, and idling this can put out some noise.
Bob

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[K24madness]

Originally Posted by HawgRyder

Don't forget to check the Pilot bearing too.
Because it is in the end of the crank, even in Neutral, clutch out, stopped, and idling this can put out some noise.
Bob

Interesting.....I never thought of that.

[matt demaria]

With car stopped and clutch pedal disengaged (out) and engine idling, there is no relative movement between the mainshaft and flywheel. It is not likely pilot bearing can generate any noise especially if it is not moving.

[HawgRyder]

Matt is right...sorry...you need the clutch disengaged and the car in gear to make the bearing do it's work.
In that way the throw out bearing is also in play.
Pilot bearings are stupid little cheap things....but can make all sorts of noise when bad.
The easiest way to extract one from the crank is to pack the hole with grease....then drive in a rod of the correct size to go into the bearing.
The hydraulic effect will pop out the old bearing like a charm.
Have fun.
Bob

[Emery G.]

Just out of curiosity did this noise just show up or has it been getting louder with time and mileage? Are you running a stock flywheel or is it an aftermarket unit?

[K24madness]

Originally Posted by matt demaria

With car stopped and clutch pedal disengaged (out) and engine idling, there is no relative movement between the mainshaft and flywheel. It is not likely pilot bearing can generate any noise especially if it is not moving.

I have been doing the checks with the clutch depressed to eliminate gear rattle from the LWFW. I will recheck with the clutch disengaged. Good tips thanks guys.

[K24madness]

Originally Posted by Emery G.

Just out of curiosity did this noise just show up or has it been getting louder with time and mileage? Are you running a stock flywheel or is it an aftermarket unit?

LWFW.

The noise was present when I bought the car. I have not put many miles (3k maybe) on the car. The noise gets louder at times. I don't think it has changed much since I got the car but it's hard to say for sure.

[AlfonsoR]

K24,

where do you live? If you're in the Houston area, I wouldn't mind coming by to help a little if you decide to drop the engine yourself.

[HawgRyder]

Just had a thought.
Do you have one of those long probe stethoscopes?
Parts suppliers like Pep Boys etc sell them fairly cheap.
With that tool you might be able to determine whether the sound is coming from the front or back of the engine.
Bob