# I think my alternator finally gave up with only 162k miles



## obrut (Oct 30, 2002)

Just went to start my truck to run out and the battery voltage was down to 9. This is a 2000 NBS GMC sierra 2500 6.0L I drove home from work on Friday and it seemed fine, tonight was the first time I started it since then. I haven't had a chance to check anything yet but the truck does have 162,000 miles and it is the original alternator. I did add duel batteries and my truck does not have the factory plow prep so I think it has the smaller output alternator. So if I have to replace it is there something better that I can get? Can I/should I rebuild mine with better parts?


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## 2COR517 (Oct 23, 2008)

Rebuilding alternators at home is a long lost art. It just doesn't make sense anymore. You can buy a rebuilt for less than the special order parts would cost you.

Find out what size yours is first, there may be an upgrade available at AutoZone, Napa, etc.

You can always get crazy here:

http://www.dbelectrical.com/c-5273-high-output.aspx

How many amps would you like today, sir?


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## obrut (Oct 30, 2002)

I checked it this morning with my meter and the alternator was jumping between 5-6 volts, i could see the gauge in the truck jumping around too. I guess maybe the regulator is bad? I did some searching last night on this site and it seems like if I go with the bigger 145 amp alternator I need to run a different belt size. Also something about rpms and pulley size.


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## 2COR517 (Oct 23, 2008)

Could be the regulator, brushes, bad diode(s), bad field winding(s). Either way, the problem is internal to the alternator.

As for the belt, sometimes the old one will work, but not always. Time for a new belt anyway.


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## obrut (Oct 30, 2002)

2COR517, thanks for the help,

auto parts has a stock replacement re-man for $89.99 with a one year warranty or a lifetime warranty for $124.99. Both are re-mans, not sure how well these would be on a plow truck, do have experience with the re-man alternators?

I think my truck has the 105 amp, with the dual batteries I never really had a problem plowing, but just like a lot of things it could always be better.


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## 2COR517 (Oct 23, 2008)

100% new is better. But all the components are tested on the remans, and many parts are new. I'm guessing the case and field windings would be reused, maybe the rotor. Brushes, bearings, diodes are going to be new in a reman. And lifetime warranty is definitely the way to go, especially on a plow truck. Looks like 105 amp is stock. If you do lots of plowing, that's marginal even with dual batteries. I put a 155 amp from Napa in my 97. Made a huge difference, but by the time I bought the high output charging kit, I had over $300 in it.

You definitely want to upgrade your charging circuit, regardless of the size alt you get. Do some looking around here, it's been gone over dozens of times.


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## obrut (Oct 30, 2002)

well today my re-manufactured alternator went out, I was driving down the street and I noticed the battery light turned on. I looked at the volt gauge and it was around 18v, not good. I was only a block from home so I just idled back home. At idle the volts were at 14, a little bit of gas and they would jump up.

Anyway the auto parts store does not have the replacement 105amp that I had on there. They have the 135amp and they said it will fit my truck, and it is new with lifetime warranty, I just have to pay the difference. 

My truck (2000 NBS GMC 2500LD) has dual batteries and I have added 4 gauge charging wire to the battery in addition to the factory charging wire. I also added three extra ground wires. I installed the new 135amp alternator and it went right on. The belt was a little tough to get on, but I got it on. Everything seems ok but since I went from a 105amp to a 135amp is there anything else I need to change or do?

Tim


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## sweetk30 (Sep 3, 2006)

better check i think there is 2 diffrent belts for the alt size. if tight now might be to tight and cause problems.


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## obrut (Oct 30, 2002)

The pulley was only slightly larger, but I was thinking about getting the right belt anyway, thanks. I think I just need one for my truck, year model, but with the 135amp alternator. I'm going back by the auto parts store tonight, I'll see what they have.


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## jklawn&Plow (Jan 8, 2011)

Are both batteries good. If connected directly together are they at a a similar voltage?


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## obrut (Oct 30, 2002)

both batteries are about 5 years old, I haven't checked the voltage on them, will this cause problems like I had with the alternator over charging?


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## obrut (Oct 30, 2002)

Ok I replaced the belt with the right length one, didn't want to have to think about it if I'm out plowing anytime soon. I also checked both batteries with the truck off and they are both at 13.05 volts.


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## sweetk30 (Sep 3, 2006)

average life span for batterys these days is 5-6 years under normal conditions.


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## ontario026 (Dec 22, 2008)

I put a DB electric 250A alternator on my 2000 6.0L NBS silverado and at the same time put the biggest interstate battery that would fit in the stock location. I also added the fuse kit that DB sells to upgrade the charging link from the alternator to the power post, as the stock wire is fairly small gauge. I probably got my hopes/expectations up when I upgraded, but I expected less voltage drop when operating the plow, a dual batt install would probably do wonders as well with the bigger alternator....

if you were closer, and in the same country, I'd give you my old stock alternator, it was working fine when I removed it... mind you it probably had about 144K miles on it when I removed it...

Matthew


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## jklawn&Plow (Jan 8, 2011)

To check the battery voltages the batteries need to be disconnected from each other. Just removed both negative terminals and then put the meter on them. They probably won't read the same. You should probably take them out and have them load tested. That is the only way to see if they have Amp-hours in them (not the equivalent of 8 AAA batteries that have 12V but only enough power for the radio). It seems like if one or both batteries were going it would put a lot of extra work on the alternator.


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## sweetk30 (Sep 3, 2006)

and if doing 2 batterys then must be the same brand/size/age/capacity. or you can get draw or overload from 1 to the other. its basicly a fighting battery story if not all the same.


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## jb1390 (Sep 23, 2008)

The size/capacity will not matter when wiring batteries in parallel. Age is important however. If you have one battery go bad, it can kill the other.


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## jklawn&Plow (Jan 8, 2011)

I am going to put in two new BAT 75XDT800 batteries from Napa or better. I had one of these in my 1500 with boss plow and lights never dimmed. Had 13-4801 alternator upgrade.


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## obrut (Oct 30, 2002)

discounted the batteries from each other and one showed 12.94 and the other was 12.91. I found the receipt for the batteries, I bought them on 11-29-07. So the batteries are actually only 3 years old. I think everything is good, plow and truck both seem to work as they should, knock on wood, thanks for the help.

Tim


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