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So I drove the truck without the belt. There is no noise. Since I have a new water pump and idler, it must be one of three things. Alternator, AC compressor or the idler on the tensioner. All three turn nice as can be by hand.

The tensioner itself is old, but I had to switch the idler on it because I needed one without grooves. I think it is brand new, but I’m not sure because I have a lot of parts, new and used in a box. (It looks new)

The AC compressor is new 5 years ago, but it has just been sitting in a box during that time.

The Alternator is used. I spun it with a drill just now and it turns nice. (I don’t know if the drill turns as fast as the motor.)

Im really at a loss. I’m thinking of ordering a new alternator.
The rear bearing on my 10 or 12si is a small needle roller bearing and has very little room for lube IMO that is the reason for it's short life span, when there is no side loading on it it was near impossible to notice it so you might pull the Alt. and split the case to visually inspect I'd look for the existence of lube as well as signs of excess heat build up a IR thermometer might also give you some info if you can get a reading of just the area of the bearing.
 
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I bought my hx30 used. It had some play in the shaft. (Not much) Anyways, after a couple thousand miles, I hear a whistle. It’s not the normal turbo whistle. This sound is at a constant cruise when the boost is at about 10-12. If I let off, it goes away. If I put my foot in it to make 20 plus boost, it also goes away. It almost sounds like belt squeal, but I have ruled that out.

Would that turbo shaft play make that kind of noise?
If there was any noticeable movement in the shaft either up and down or in or out, you should have fixed the bushings/thrust bearing before installing it ! Check all the joints, bolts any place something disconnects from the turbo, such as air tubes to the head, exhaust fittings and gaskets. Since the noise gets worse under load/ boost this makes it obvious or should. Those clamps on the rubber hoses can be a source of noise by not holding the seal. That's one I've found before. If the gasket at the mount flange is loose you will loose drive pressure which will drop your boost.
 

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I would be looking at the alternator diodes...this happened to me a long time back had me looking at everything but.
remove ALL the wiring from the rear of the alternator so it is not charging and go for a spin, it only takes 1 diode to fail to make a whistle or whine sound at different RPM's. a failed diode may not throw the alternator light on and will slowly leak the battery down over time.
 

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So I drove the truck without the belt. There is no noise. Since I have a new water pump and idler, it must be one of three things. Alternator, AC compressor or the idler on the tensioner. All three turn nice as can be by hand.

The tensioner itself is old, but I had to switch the idler on it because I needed one without grooves. I think it is brand new, but I’m not sure because I have a lot of parts, new and used in a box. (It looks new)

The AC compressor is new 5 years ago, but it has just been sitting in a box during that time.

The Alternator is used. I spun it with a drill just now and it turns nice. (I don’t know if the drill turns as fast as the motor.)

Im really at a loss. I’m thinking of ordering a new alternator.
get a can of belt dressing spray ( available most parts stories.. and any big farm parts store) ... spray belt when running.. if you got oil on belt it can have deposits and squeal... also worn pullies can lose grip and the belt will squeal.. if the belt dressing spray shuts it uo.. it is likely belt related... you can take the belt and buff it on a wire wheel.. it could shut it up as those belts like to glaze... and you can ruff up the pullies a bit and that can help with a lack of grip.. or you can replace the belt and tensioner.. as tensioners can lose tension over time.. and the belt will squeal..
 

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Discussion Starter · #25 ·
The rear bearing on my 10 or 12si is a small needle roller bearing and has very little room for lube IMO that is the reason for it's short life span, when there is no side loading on it it was near impossible to notice it so you might pull the Alt. and split the case to visually inspect I'd look for the existence of lube as well as signs of excess heat build up a IR thermometer might also give you some info if you can get a reading of just the area of the bearing.
I ordered a new alternator. If that cures it, I will take apart this one. If it doesn’t fix it, I have a spare. I may try the IR gun idea while I’m waiting for new one.

If there was any noticeable movement in the shaft either up and down or in or out, you should have fixed the bushings/thrust bearing before installing it ! Check all the joints, bolts any place something disconnects from the turbo, such as air tubes to the head, exhaust fittings and gaskets. Since the noise gets worse under load/ boost this makes it obvious or should. Those clamps on the rubber hoses can be a source of noise by not holding the seal. That's one I've found before. If the gasket at the mount flange is loose you will loose drive pressure which will drop your boost.
At this point, I believe it is belt related because it seemed to go away with the belt removed.

I would be looking at the alternator diodes...this happened to me a long time back had me looking at everything but.
remove ALL the wiring from the rear of the alternator so it is not charging and go for a spin, it only takes 1 diode to fail to make a whistle or whine sound at different RPM's. a failed diode may not throw the alternator light on and will slowly leak the battery down over time.
I have never heard of diodes making noise, but Im open to all ideas. I will try the “no load“ idea.

get a can of belt dressing spray ( available most parts stories.. and any big farm parts store) ... spray belt when running.. if you got oil on belt it can have deposits and squeal... also worn pullies can lose grip and the belt will squeal.. if the belt dressing spray shuts it uo.. it is likely belt related... you can take the belt and buff it on a wire wheel.. it could shut it up as those belts like to glaze... and you can ruff up the pullies a bit and that can help with a lack of grip.. or you can replace the belt and tensioner.. as tensioners can lose tension over time.. and the belt will squeal..
I thought you don’t use belt dressing on serpentine belts. In any case, the belt is new and most of the pulleys are new. I may need a new tensioner.
 

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I ordered a new alternator. If that cures it, I will take apart this one. If it doesn’t fix it, I have a spare. I may try the IR gun idea while I’m waiting for new one.



At this point, I believe it is belt related because it seemed to go away with the belt removed.



I have never heard of diodes making noise, but Im open to all ideas. I will try the “no load“ idea.



I thought you don’t use belt dressing on serpentine belts. In any case, the belt is new and most of the pulleys are new. I may need a new tensioner.
any spill on the belt and it can be contaminated... try the belt dressing trick...its just a spray can .. you spray on while running... I'd bet it will shut up.. for a while... which likely means the belt is contaminated, or loose... but if you spray at each pulley.. you may get an identity as to if you have a pullet that is too polished down...
 

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One thing you mention that has me wondering. You changed the pulley on the tensioner from grooved to smooth. Aren't tensioners that are made with the different style pulleys made with different spring actions? All the 4bt tensioners I found in my industrial catalog are smooth but they vary depending on their location position on the belt. Have you got a photo or diagram of your belt routing and tensioner placement?
 

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Discussion Starter · #28 ·
any spill on the belt and it can be contaminated... try the belt dressing trick...its just a spray can .. you spray on while running... I'd bet it will shut up.. for a while... which likely means the belt is contaminated, or loose... but if you spray at each pulley.. you may get an identity as to if you have a pullet that is too polished down...
When I said the belt is new, I ment it is literally brand new. I recently changed my tensioner configuration and had to get a different length. I might have 20 miles on it. I have used belt dressing on deep groove pulleys. Didn’t know it was for serpentine. I’ll give it a try.

One thing you mention that has me wondering. You changed the pulley on the tensioner from grooved to smooth. Aren't tensioners that are made with the different style pulleys made with different spring actions? All the 4bt tensioners I found in my industrial catalog are smooth but they vary depending on their location position on the belt. Have you got a photo or diagram of your belt routing and tensioner placement?
I was not aware of differnt spring rates. (That means nothing) Maybe I could measure the spring rate with a torque wrench. I have a 6BT with a tensioner and smooth pulley stock. I could swap the whole tensioner off that to my 4BT and see if it makes a difference. I don’t have a good pic of the 4BT, but it’s the same configuration as this 6BT.

Tire Wheel Automotive tire Motor vehicle Blue


The only difference on my 4BT is the fan hub is replaced with a smaller idler.
 

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Seems odd no one has mentioned using a stethascope to find the noise? I know this isn't always the final solution to finding noises but it should be the second step after an un aided ear. In the past I have had to deal with noises that made us guys in the shop I worked in scratch our heads a few times, Had a few Cummins and Duramax's and Powersmokes plus about every other animal come along with some tough track downs and even found some noises to be caused by such minor misalignments they were not obvious at first. It's really a tough one when the parts have the pulley's pressed on from the factory such as the water pumps on Cummins. Those that have pressed on bolt hubs are not out of suspicion either. Point is, as I mentioned about the air leaks, clamps and bolts can and do come loose and it's a simple task to check for any. Flanged items can warp from heat and pressure, such as the air horn on the intake. Somewhere I thought I saw where it was mentioned that the noise got worse under load so at that, I would not be considering alternator or belt noise until after the air system had been eliminated. Wasn't the turbo removed before the noise came along? Another reason to be looking there first. Either way the process of elimination most always find it is the last thing you look at !
 

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Discussion Starter · #30 ·
Seems odd no one has mentioned using a stethascope to find the noise? I know this isn't always the final solution to finding noises but it should be the second step after an un aided ear. In the past I have had to deal with noises that made us guys in the shop I worked in scratch our heads a few times, Had a few Cummins and Duramax's and Powersmokes plus about every other animal come along with some tough track downs and even found some noises to be caused by such minor misalignments they were not obvious at first. It's really a tough one when the parts have the pulley's pressed on from the factory such as the water pumps on Cummins. Those that have pressed on bolt hubs are not out of suspicion either. Point is, as I mentioned about the air leaks, clamps and bolts can and do come loose and it's a simple task to check for any. Flanged items can warp from heat and pressure, such as the air horn on the intake. Somewhere I thought I saw where it was mentioned that the noise got worse under load so at that, I would not be considering alternator or belt noise until after the air system had been eliminated. Wasn't the turbo removed before the noise came along? Another reason to be looking there first. Either way the process of elimination most always find it is the last thing you look at !
Post #9 suggests a stethoscope and a few posts later I had bought one and found it to be of no use. Hard to use it when it’s driving. In this truck it’s not impossible because of mid engine, but it’s still kind of scary. The turbo has not been messed with for a long time.

The sound actually goes away when the boost is over 15”. I think that is because the engine is excellerating. It’s very elusive sound. Could be bearing, boost leak or belt. But when I drove it with out the belt, it was gone. So I’m pretty sure it is the belt or a belt driven item.

I ordered a new AC clutch bearing. The sound doesn’t change whether the AC is on or off, but that bearing is turning in both cases. It was rather cheap (as compared to an alternator) I’m hoping it’s not much work to change.
 

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Discussion Starter · #31 ·
Well today I got the new alternator and a bearing for the AC clutch. I picked the alternator first and swapped it in. Took it for a drive and………..





No Noise! God it was nice to hear only the sweet whistle of the turbo. I only drove for about five miles, so I won’t say it’s categorically fixed, but I have high hopes. It really makes me mad I didn’t try running it unloaded as some one suggested. One thing I did notice was the nut that held the pulley on was really hard to get off. I wonder if it got hot on that end.

Anyways, I’m pretty happy right now. Thanks to all that helped.
 
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Well today I got the new alternator and a bearing for the AC clutch. I picked the alternator first and swapped it in. Took it for a drive and………..





No Noise! God it was nice to hear only the sweet whistle of the turbo. I only drove for about five miles, so I won’t say it’s categorically fixed, but I have high hopes. It really makes me mad I didn’t try running it unloaded as some one suggested. One thing I did notice was the nut that held the pulley on was really hard to get off. I wonder if it got hot on that end.

Anyways, I’m pretty happy right now. Thanks to all that helped.
Excellent then.
Lots of good info here helps to do the least expensive tests first, now take the old alternator apart remove the diode plate disassemble it and test each diode for a faulty one give the bearings a spin at the same time check for a grumbly one. I am sure it will be a diode. rgds
 

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Discussion Starter · #33 ·
Excellent then.
Lots of good info here helps to do the least expensive tests first, now take the old alternator apart remove the diode plate disassemble it and test each diode for a faulty one give the bearings a spin at the same time check for a grumbly one. I am sure it will be a diode. rgds
So are you saying that it will still charge with a bad diode? It charged real good. I’m not very good with electronics. I will probably take it somewhere if I can find a place. These days nobody does this stuff.
 

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You mentioned the pulley being very tight. It is supposed to be very tight. Torque rating to that nut is pretty high. Alternator stores have a special unit to install that pulley.
 

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Discussion Starter · #35 ·
You mentioned the pulley being very tight. It is supposed to be very tight. Torque rating to that nut is pretty high. Alternator stores have a special unit to install that pulley.
I installed that pulley a short time ago with an impact. The same impact couldn’t get it off. (It took it off multiple other times.)
 

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Hi Yes it will still charge with "a" bad diode but will eventually leak the battery down. You now have the alternator off the vehicle so get yourself a good quality multimeter meter and check the flow of current from the large + terminal to alternator body, then switch the leads round and see if the meter registers any difference. If you receive no reading in one direction but a large reading in the other direction then diodes are good. If the mulimeter needle moves no mater which way you connect it then diode or diodes are bad.
I contract to Nippon Denso and other electronic places here in Japan and have seen and herd real weird sound coming from diodes and other solid state components. A high pitched whistle sound is common from diodes giving it up, giving the impression of turbo troubles, the higher the engine RPM the higher the whistle...... Hope this helps in the future.

True very few places repair this stuff, those days are mostly gone, Throw away society now, Sad.
Wages and time fees have outstripped the cost of parts and repair.
 

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Discussion Starter · #37 ·
I will try it.

One of the things about this alternator. A guy on another forum said it’s very good quality because it had 12 diodes instead of the normal 6. Does that sound right? If that’s true, would a bad diode have the same effect?
 

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True to a point, I have never seen 12 diodes installed alternator....yet, maybe an aftermarket or custom unit of some sort. Most common are 6 diode plate alternators. And yes, same effect. It only takes 1 bad diode to generate the whistle noise.
 
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