Loud intermittent high pitched scraping/grinding noise ?

[Diggs]

 1983 720 z24, 5speed.  85,000 miles. 

 

I recently started getting this awful high pitch scraping/grinding sound from the engine, and can't figure it out.  I can hear the noise everywhere in the engine compartment so its hard to pinpoint the origin.

 

Thought it might be a bad pulley or tension-er?

 

Thought it also could be a worn clutch but it makes the noise in idle, and goes away randomly through all speeds.   When i let off the clutch @ high speeds it completely goes away.  Also,  seems to go away in 5th gear, but it does get a little louder with acceleration.  

 

any help would be greatly appreciated.   I will try to post an audio clip of the sound.

  

[datzenmike]

High pitch sounds or squeaks under hood...

 

Low power steering fluid.

 

Loose or glazed fan belt, power steering belt or air conditioner belt. Both the PS and AIR have a tensioner adjustment using an idler pulley. The bearing in it may be going bad. It's time consuming but you could remove each belt in order one at a time and run the engine briefly to eliminate or confirm the cause. While the belts are off inspect and or replace them and check the idler pulleys for excess play or roughness.

 

Bearing in alternator going bad.

[wayno]

Does it make the noise when your not moving while the clutch pedal is pushed in when it's in gear?

[Charlie69]

Take a the wooden handle off a toilet plunger  (I prefer to cut down a wooden broom handle).  place your thumb over 1 end and stick the other end solid against various parts of the motor, now the end with your thumb over it place against one of your ears, preferably a good ear, and listen until you locate the area the noise is generating from.  This works similar to a stethoscope.

[Diggs]

It does make noise when not moving 50 % of the time. (clutch pedal in).    I will try removing the belts and replacing the pulleys and start from there,   will keep you updated,  Thank you for the input  !   ~(*!*)~

[720DEBORAH_OWNER]

Im betting on throwout bearing......

[720inOlyWa]

Sounds like a throwout bearing to me, too. An easy test to see if it is a tensioner pulley is to shoot a little white lithium grease spray into the tiny gap where the bearings live- one pulley at a time. I use the little red tube to really get it in there. I live dangerously and so I did this very carefully with the engine running. If it is the pulley bearing going out, it will usually quiet down briefly, until the grease is gone. It doesn’t always work, but it has helped me isolate which pulley was in trouble.

[720DEBORAH_OWNER]

Sounds like a throwout bearing to me, too. An easy test to see if it is a tensioner pulley is to shoot a little white lithium grease spray into the tiny gap where the bearings live- one pulley at a time. I use the little red tube to really get it in there. I live dangerously and so I did this very carefully with the engine running. If it is the pulley bearing going out, it will usually quiet down briefly, until the grease is gone. It doesn’t always work, but it has helped me isolate which pulley was in trouble.

Another way to isolate is to CAREFULLY use a pry bar to add or remove a bit of load on the suspect. If it is your culprit the pitch of your noise will change. Example: one can pry a bit on the body of the suspect accessory this works best on non-serpentine systems. Serpentine's reqire more finesse. Adding tension anywhere adds it everywhere.

 

But by far the best way is to use a mechanics stethoscope on the body of the device that the suspect pully's shaft is mounted in. This method is VERY definitive. Doesnt matter if the noisy bearings are in the pully itself like a tensioner or if the shaft is fixed in the pully and the bearings are inside the device, like an alternator or power steering pump.

[datzenmike]

It does make noise when not moving 50 % of the time. (clutch pedal in).    I will try removing the belts and replacing the pulleys and start from there,   will keep you updated,  Thank you for the input  !   ~(*!*)~

 

 

Im betting on throwout bearing......

 

The throw out bearing is only in use when the clutch pedal is going down, is down or is coming up from the floor... or, in the act of disengaging or engaging the clutch. When driving it's not moving and definitely not under any load load so it can't be making any noise.

[720DEBORAH_OWNER]

 1983 720 z24, 5speed.  85,000 miles. 

 

I recently started getting this awful high pitch scraping/grinding sound from the engine, and can't figure it out.  I can hear the noise everywhere in the engine compartment so its hard to pinpoint the origin.

 

Thought it might be a bad pulley or tension-er?

 

Thought it also could be a worn clutch but it makes the noise in idle, and goes away randomly through all speeds.   When i let off the clutch @ high speeds it completely goes away.  Also,  seems to go away in 5th gear, but it does get a little louder with acceleration.  

 

any help would be greatly appreciated.   I will try to post an audio clip of the sound.

 

 

The throw out bearing is only in use when the clutch pedal is going down, is down or is coming up from the floor... or, in the act of disengaging or engaging the clutch. When driving it's not moving and definitely not under any load load so it can't be making any noise

 

Again Mike is right here. i misread the orginal post........ How about Pilot bearing/bushing? 

[wayno]

He has not been back since the last post he made, but if were my truck, I would check the level and color of the transmission fluid, and rule that out.

[datzenmike]

 How about Pilot bearing/bushing? 

 

The pilot bushing and the transmission input shaft inside it would be connected together when the clutch is engaged or pedal in the up position. They would be both spinning if the engine was running but together as a unit. Only when the clutch was disengaged would they uncouple and be free to move at different speeds.... then they could make noise.