I am trying to solve an intermittent squeal on my truck. At first I thought it was just the serpentine belt, or one of the components driven by the belt. The squeal happens right after startup, at idle, while I am driving, with boost, without boost, in any gear, with the AC on, with the AC off, and even with the clutch pedal fully depressed.

1. First thought it was my tensioner idler pulley. Replaced it and still have the intermittent squeal.
2. Thought it might be one of the other components driven by the belt.
3. Removed the serpentine belt, and rotated everything by hand.
4. Top idler pulley spins smooth and is tight.
5. AC sheave pulley spins smooth an is tight.
6. Power steering sheave pulley spins smooth and is tight.
7. Fan pulley spins smooth, no end play, no slop and is tight.
8. Water pump spins smooth, and is tight.

I used an engine stethoscope, and could not pinpoint the exact location of anything significant.

Next I removed the serpentine belt from the engine, and fired the engine up. The intermittent squeal is still there. Now I'm stumped, and alarmed.

I took the intake off between the turbo and the intake filter. The turbo impeller looks good, no obvious damage or problems. There is no end play in the shaft. There is a very small amount of axial play, but according to Holset some is acceptable. Spinning the impeller shaft shows no signs of problems. By the way, this is the Holset HE351CW turbo.

Next I start up the engine, without the intake boot to the turbo, and also without the serpentine belt installed. I'm not certain that the sound is any louder without the intake connected.

So, like I said, I'm stumped. It is obviously an engine problem, and definitely a sound like a dry rotating bearing, or bearing going bad.

Is it possible to rebuild a turbo, or do you have to completely replace it?
Is it possible that this is the CP3 making this noise?
Is there anything else that this type of noise could be?

 

Sounds like it's the pilot bearing/bushing.

Next chance, check up near the bell housing with the stethoscope.

 

I'm not certain that this is the pilot bushing making this noise. With the engine running, transmission in nuetral, parking brake on, the clutch is engaged with the flywheel. Therefore, the engine crankshaft and the transmission crankshaft are turning in unison, and the pilot bushing would technically be stationary/not rotating. The pilot bushing should only rotate when the clutch pedal is pressed to disengage the clutch from the flywheel.

 

Right. But even when the input shaft on the transmission isn't turning, it's still riding in the pilot bearing.

 

I did some more investigating. When I first cranked up the motor, I kept the clutch pedal pressed in and waited for a long time, no squeal noise occurred. Then I let off the clutch, and soon after it started making the squealing noise. I press the clutch and the noise goes away. I played with it several times pressing down all the way or even just partially. Everytime the squeal would come and go with the releasing and pressing of the clutch pedal. So I believe the culprit is the throwout bearing. I bought a new one, now I just need the time to pull the transmission and put it in.

 

Update

I removed the transmission, and the clutch throwout bearing was bad. The pilot bearing was still good. Removed the old throwout bearing, cleaned everything up, lubed everything with new grease, installed new throwout bearing, and re-installed the transmission. Working smooth like brand new again.

 

Glad you got it!