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Discussion Starter #1
So I go out to my truck tonight... I've got the idea in my head that I'm going to make an uneventful trip home, but alas, it was not to be.

So I run out to the truck (it is SERIOUSLY COLD here) and jump in. Turn the key, wait for the glow plugs, and fire it up. Instantly squealing sounds start coming out from under the hood... I open the hood and the alternator is locked up. Great.

After a few seconds the alternator started spinning but kept making squealing sounds all the way home (not the belt - the alternator itself).


Just figured I'd complain a bit...
 

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that really sucks, we had the same problem on my dads 92 chevy with the 4.3 in it. the alternator siezed up while we were elk hunting. we were way out of cell phone coverage but luckily it was all downhill so i kicked it in neutral and away we went!!
 

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Well as long as we are complaining I had the alternator off my Mack four times this afternoon. It never locked up or squealed but I did manage to get it to charge the batteries in 35 seconds at 19 volts. I hope the batteries will forgive me for my mistakes.
 

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be thankful you don't have a serpentene belt. i lost a alt belt going over pass in northern california in dad's 85 suburban had a spare belt but no deep well 15mm to loosen power steering had to go to next town and belt up there.
 

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Discussion Starter #5
I'm just glad it unfroze... It was cold enough I was about ready to put it in gear and drive home with it locked up... ):h The funny thing was that by the time I got home it was spinning freely and making relatively little noise.

I have a digital voltmeter installed in my truck and it read 11.7V with the alternator locked up, 13.1V with it spinning but making noise, and 14.6-14.7V with it spinning and not making noise... :confused:

You guys with the serpentine belts are very unlucky... ):h I love the v-belt setup... Just remove a couple bolts and the alternator comes right off. :cool2:
 

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years ago we went out wood cutting on fed forest a good hour drive from nearest town and buddy's had a gasser chev with a serpentine belt and a electric winch. well they thought you could use this winch to your hearts delight so they drug every log out to them. well didn't have dual batteries and by the middle of the day the alt. froze up. had to leave rig in woods and they jumped in with us. came back next day with alt.
 

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High Sierra 2500;1579160; said:
So I go out to my truck tonight... I've got the idea in my head that I'm going to make an uneventful trip home, but alas, it was not to be.

So I run out to the truck (it is SERIOUSLY COLD here) and jump in. Turn the key, wait for the glow plugs, and fire it up. Instantly squealing sounds start coming out from under the hood... I open the hood and the alternator is locked up. Great.

After a few seconds the alternator started spinning but kept making squealing sounds all the way home (not the belt - the alternator itself).


Just figured I'd complain a bit...
Many Delco 10 and 12SIs will squeal at the rear needle bearing when cold.
A genuine mechanical lockup would have to be a front bearing in most cases.

I can't speak specifically about your engine and problem but from what you describe it is a common sounding event with 6.2s and cold starting. From many of the ones I had to figure out - it WAS the belt making the noise even though it did not overtly appear that way. So some of this may, or may not apply to your situation. Often the belt is not wide enough, and when a large electrical demand is put on the alternator - it stops turning - appearing to be locked up.

Problem #1 - is simply the wrong belt. If you go to a local NAPA, Autozone, Parts Amerca, etc. - they will sell you the wrong belt. It will fit and look fine - but is NOT the correct one. Once slighly worn, it will slip under a high load no matter how tight you make it. The do that to cut down on inventory - and enables them to have ONE belt that fits MANY applications. If you look at their small print - when looking up the belt - it will show the belt they prefer to sell you - along with a non-stocked belt that is called the "preferred GM belt." The preferred belt is usally 1/64" wider or more. These belts grip on the sides and cannot be allowed to bottom out. When a 6.2 is started cold, a tremendous amount of battery current is used to crank the engine and heat the glow plugs. Once started - there is a huge demand put on the alternator to recharged the batteries quickly - so it turns harder just like someone is applying a brake to it.

Problem #2 is the diesel-pulse surge of the 6.2 diesel and it's effect on belts on an older 6.2 that has a plain steel crankshaft pulley. The later, post 1985 rubber-cushion pulley makes a big difference. With the older steel pulley, no matter how tight you make the belt there will be pulse-cycles when it is loose. Just eyeball it with your engine idling and watch it dance around - if you have a steel bottom pulley.
 

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Discussion Starter #8
In this case the alternator suffered a mechanical failure. It doesn't have anything to do with cold starting, that was apparently just a coincidence. I will be tearing the alternator down either later today or tomorrow and we will see the results of the failure.

This alternator has had a bit of a rough life... It was locked up from sitting when I got the truck and appears to have been taken apart before, so who knows what has happened to it in its previous lives.
 

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i have had issues with the wrong belt with me if i remember it was the angle of the cut was wrong. also found my fan pulley was cracked when i changed my water pump. now i hear my ac pump grumbling when i fire her up and it is worse when cold. seeing ac oil on acc. around ac pump. good clue to rebuilt pump time. good luck let us know what you find.
 

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High Sierra 2500;1580637; said:
In this case the alternator suffered a mechanical failure. It doesn't have anything to do with cold starting, that was apparently just a coincidence. I will be tearing the alternator down either later today or tomorrow and we will see the results of the failure.

This alternator has had a bit of a rough life... It was locked up from sitting when I got the truck and appears to have been taken apart before, so who knows what has happened to it in its previous lives.
If you've got the older 10 or 12SI, there's nothing that can crap out and make it sieze other than the one little sealed ball bearing in front - unless it's really hammered and completely fallen apart. The back only has a open needle bearing. If it goes, usually everything else goes with it including the housing.

The newer style alternators (can't remember what year they start) - but I think they are only used in sepentine setups - have two ball bearings.
 

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farmer0_1;1580683; said:
i have had issues with the wrong belt with me if i remember it was the angle of the cut was wrong. also found my fan pulley was cracked when i changed my water pump. now i hear my ac pump grumbling when i fire her up and it is worse when cold. seeing ac oil on acc. around ac pump. good clue to rebuilt pump time. good luck let us know what you find.
The problem I've encountered many times is the width - not angle. Angle is supposed to be 36 degrees. But the part's listings and the guy(or girl) behind the corner is the problem. If you go to just about any major auto parts store - and ask for an alternator belt - for let's say an 87 Chevy Suburban with 6.2 diesel - they will hand you a Gates 7480 or equiv. It is a 3/8" wide belt. If you ask for their "premium" belt - they will sell you a 13/32" wide belt. Still not correct and still too narrow. In their list - is a little note about the non-stocked belt that is the correct and "preferred" GM belt - Gates 5725 which is 7/16" wide. All this would be fine if the counter-person told you - but they usually do not - and I assume many don't even notice.

This problem exists with many gas engines too - encountered it back in the early 70s.
I learned sort of the hard with the 6.2s. When I first got my 87 6.2 Suburban - from the original owner - I changed all belts, hoses, injectors, etc. First cold morning - the alternator/belt squealed like crazy. It never happened before - not even to the original owner. But . . . he had all his service work done at the dealer - NO aftermarket parts. This situation led me to several belt-changes, then super-tighening my belt and having the waterpump go bad shortly after. Then, I ordered a larger diameter alternator pulley - that has more belt gripping area. That in turn threw my tachometer reading off since it runs off the alternator. Finally, one day - while down at NAPA - I got behind the counter - and looked at the paper Gates belt book (not the computer). There was the answer - and I was really ticked off about it. After some complaints, the NAPA owner gave me (after ordering them) two new correct belts and gave me my own Gates belt and hose cross-reference catalog. It is very good to have.
Some time later, I put my original smaller alternator pulley back on, with the correct belt, and all was fine. Since that time -over 10 years ago, I've encountered the same problem with many 6.2 diesels - since most people buy belts aftermarket and just about always get the wrong belt.
 

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Discussion Starter #13
Well, I fixed it. The bearings were a bit dried out, but by some miracle they were pretty much intact although they are a bit worn from being run partially dry... I lubricated the bearings and it works good now. I'm guessing some water got in the bearings and caused it to freeze up when it cooled down. It will probably come back and give me more troubles one of these days, but at least this way I don't have to buy a new alternator right now...
 
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