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How to install dual alternators - NO fabrication required!!!

This is a discussion on How to install dual alternators - NO fabrication required!!! within the Technical / Maintenance forums, part of the General Discussion category; You heard that right folks, I will show you how to install dual alternators on your Chevy pickup, with NO ...

  1. #1
    1986 ATC250R FTW Nick_R_23's Avatar
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    How to install dual alternators - NO fabrication required!!!


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    You heard that right folks, I will show you how to install dual alternators on your Chevy pickup, with NO FABRICATION REQUIRED!!! This is a 100% bolt on application that uses ALL oem parts that you can get from your local junkyard for almost no cost. As a plus, it will get rid of that unsightly left side A/C and smog pump bracket for a much smaller one. This setup is meant for trucks that have the 2 piece aluminum bracket set.

    Before you read any further THIS WILL NOT WORK ON A/C OR SMOG PUMP EQUIPPED TRUCKS!!

    What you will need:

    Go to your local junkyard and find a Chevy Astro van with a 4.3L V6. The one I pulled my bracket from was early 90's (first gen), however I believe the bracket is the same throughout the 2nd gens also. You will need the left side aluminum bracket off the engine, along with the 3 bolts that hold it to the head, and the 2 or 3 bolts that secure the alternator (depends on if the alternator you are using has an internal or external fan, however both style alternators will fit this bracket).

    What you should end up with is this:



    As you can see the new bracket is quite a bit smaller then the original one on your engine:



    Install the new bracket onto the head using the 3 bolts, followed by the alternator. If you are using an internal fan alternator, it will have a 3rd bolt for the rear. If you are using an external fan alternator, it will not use the rear bolt. I am using 2 105A external fan alternators on my engine. Belt routing will be the same as normal. (Shown below). You might need a new belt, (mine is too long in the picture below). The correct belt is 94" long, part # 25-060935 from Napa.



    How you wire your 2nd alternator is up to you. I have dual batterys on my truck so I will have one alternator power the truck and the 1st battery, and the 2nd alternator will power the 2nd battery and whatever accessories I want to run (lights, plow, camper, winch, etc) and will be on a seperate circuit then the rest of the truck.

    I hope this has been helpful as I know many people have been trying to find a way to run dual alternators in these trucks for years without major fabrication. Please be smart when installing and wiring these as I wouldnt want to see any members trucks get burnt up because of improper wiring or installation, so if you dont think you are capable of performing the work PLEASE consult someone who is. Thanks for reading and lets hear what you think!!

    -Nick
    Last edited by Nick_R_23; 09-18-2009 at 12:36 AM.
    1988 Chevy Silverado 5.9L Cummins : 1968 Ford Mustang Pro-Touring

  2. #2
    Loves GMT400 haters someotherguy's Avatar
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    Re: How to install dual alternators - NO fabrication required!!!

    Very cool mod! Thanks for the details.

    I won't be doing it though as there's no way I could stand it down here in Houston with no A/C, especially in a black truck! I can still appreciate that others would find it very useful, though!

    Richard

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    Re: How to install dual alternators - NO fabrication required!!!

    How would you go about running all your accesories off of the second battery? I'm looking at getting a slide in camper and that setup would be ideal. Do you just run a power wire to a multiple terminal board and go from there? Thanks

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    Re: How to install dual alternators - NO fabrication required!!!

    yea only people who drive beaters in houston dont have a/c.

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    1986 ATC250R FTW Nick_R_23's Avatar
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    Re: How to install dual alternators - NO fabrication required!!!

    Alright, I found the correct length belt to use on this setup. The correct belt is 94" long, part # 25-060935 from Napa.

    -Nick
    1988 Chevy Silverado 5.9L Cummins : 1968 Ford Mustang Pro-Touring

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    BNSF railfan csx7006's Avatar
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    Re: How to install dual alternators - NO fabrication required!!!

    hell i could use this

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    Supporting Gold Member GreaseDog's Avatar
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    Re: How to install dual alternators - NO fabrication required!!!

    would be good in the plow truck... hmmmm...
    77 Chevy K20 - 80 GMC K2500 (in pieces)
    90 Chevy K3500 - 93 Chevy C2500 (in pieces) - 94 Chevy K1500

  8. #8
    JoshTheCanadian
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    Re: How to install dual alternators - NO fabrication required!!!

    Quote Originally Posted by csx7006 View Post
    hell i could use this
    thanks for the thread dig.

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    BNSF railfan csx7006's Avatar
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    Re: How to install dual alternators - NO fabrication required!!!

    your welcome

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    The Good Samaritan
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    Re: How to install dual alternators - NO fabrication required!!!

    this should be in the tech articles, or a sticky at the least, before it gets lost
    1995 K1500, ECSB, 350TBI, 4L60-E, 285/75/R16

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    Re: How to install dual alternators - NO fabrication required!!!

    Hey nick what year is this set up for I have a 1970 K20 and am looking to add a second alternator to my truck, she originally came with dual batteries.... Im not set up for serpentine, I have a V-Belt 454 if possible I'd like to convert to serpentine and dual alternators on my Big Block....Can you lend some advice?
    Indy....Just in case your local to me (562)972-1471....

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    Re: How to install dual alternators - NO fabrication required!!!

    I didnt want to start a new thread since this one should answer my question if there is anyone that has any experience with it. I have an 89 2500 eclb, i also have a 90 1500 rglb, both tbi 5.7's. The 90 has the 2 piece aluminum bracket, and the 89 a steel 1 piece bracket. So far all parts have been interchangeable for me except for my alternator. Will the aluminum 2 pc fit on my 2500 without any mods? My alternator bearings are shot and i tried switching alts but they mount differently. So i figure i may as well just switch out the brackets so i can run a dual alt setup with the Astro bracket in the near future.

    Any input ???

  13. #13
    The Good Samaritan
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    Re: How to install dual alternators - NO fabrication required!!!

    bump for sticky/article.....C'mon Admins/Modz wake up
    1995 K1500, ECSB, 350TBI, 4L60-E, 285/75/R16

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    Re: How to install dual alternators - NO fabrication required!!!

    LoL he bumps it 14 minutes after i just bumped it from 4 months ago.

    But yes he is right, this info is GOLD, im sure there's alot of people that would be all over this mod. This NEEDS TO BE A STICKY !!! : )

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    1986 ATC250R FTW Nick_R_23's Avatar
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    Re: How to install dual alternators - NO fabrication required!!!

    Quote Originally Posted by Eismanx View Post
    I didnt want to start a new thread since this one should answer my question if there is anyone that has any experience with it. I have an 89 2500 eclb, i also have a 90 1500 rglb, both tbi 5.7's. The 90 has the 2 piece aluminum bracket, and the 89 a steel 1 piece bracket. So far all parts have been interchangeable for me except for my alternator. Will the aluminum 2 pc fit on my 2500 without any mods? My alternator bearings are shot and i tried switching alts but they mount differently. So i figure i may as well just switch out the brackets so i can run a dual alt setup with the Astro bracket in the near future.

    Any input ???
    The 2 piece aluminum brackets will fit ANY Chevy small block/4.3L as long as the heads you are using have the 3 bolt holes in front. This means that older 283, etc heads with one or no bolt holes will not fit, but since these heads are fairly uncommon it should not be a problem for anyone.

    Also as a side note for those of you who may not know, if you are using these brackets on a Pre-TBI engine (86 and older blocks, basiclly all 2 piece main blocks), you MUST run a Post-TBI (87+ blocks, 1 piece main) waterpump. The reason being is that because of the way the serpentine belt is routed, the serpentine waterpump rotates the opposite direction then the older V-belt waterpumps. It is a direct bolt on, but remember that you must use the fan that is matched for your waterpump as well, since the blades face the opposite direction because of the pump spinning the opposite way.
    1988 Chevy Silverado 5.9L Cummins : 1968 Ford Mustang Pro-Touring

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    Re: How to install dual alternators - NO fabrication required!!!

    I upgraded mine. This works perfectly.

    UPDATE: DO not be a cheap @$$ like me and think the old tensioner will work. YOU MUST BUY THE ASTRO TENSIONER WITH THE ASTRO BRACKET, THE TENSIONER ON THE ORIGINAL BRACKET WILL NOT WORK ON THE ASTRO BRACKET. They look identical but they're not. The truck tensioner is flat on the back and the the little knob on the back is only around a 1/4 inch, the Astro tensioner has a lip on the back to fit into the recessed bracket, and the guide knob is almost 1/2 inch.

  17. #17
    Why don't you shirt it up 07tbss's Avatar
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    Re: How to install dual alternators - NO fabrication required!!!

    bump so i can find this when i get home...guess this is another to add to the list...

    I do have one question tho....what would be the advantages of doing this instead of just buying a 200+ amp alternator??? Price maybe?? Or is it the fact that you can charge 2 different batteries without using an isolator?? Also i suppose you could just use both alternators to charge one battery right??? Thanks again for the awsome write up

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    Re: How to install dual alternators - NO fabrication required!!!

    Well you have one charging system dedicated to your system and the other dedicated to the truck like its meant to be. I took a battery tray from the junkyard and modified it to fit on the driver side which consisted of just taking the bracket off the tray and mounting it on the opposite end. I had to bend the bottom of the bracket a little, but it worked out great and now i have 2 completely seperate charging systems.

    Price is definately a factor. I did this mod for no more than $50 dollars including a free battery i found on craigslist, which is still good and holds a charge. The new belt is what cost the most at $25.

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    Registered User dave89iroc's Avatar
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    Re: How to install dual alternators - NO fabrication required!!!

    you can also use a vortec(96+) pass side bracket, the tensioner mounts different, but the otherwise it looks the same as above
    ASE Master Certified Technician

    2000 Silverado 6.0 4L80E 2wd
    *RIP*1994 Z71 SCLB 355, Dart Heads, 10.5:1 CR, PM rods, CC XR270HR

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    1986 ATC250R FTW Nick_R_23's Avatar
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    Re: How to install dual alternators - NO fabrication required!!!

    Bump for the 2011 crew!

    After nearly a year and a half, I can still say that this is the best mod I've done yet.

    I'm currently finishing up a 1 ton frame swap with this truck, and in the process, I've done a few small upgrades regarding this mod. I'm going with 2/0 gauge wire for ALL my battery cables, and upgrading to military style post connectors. I've also upgraded the distribution block feed wire with 4 gauge. I've also added another distribution block for the 2nd battery for easier attachment of accessories. On top of that, I'm going to run another length of 2/0 cable from the two positive terminals on both batteries (similar to a diesel truck battery setup), but with a disconnect switch in the middle. This way, I still keep both batteries and charging circuits seperate, but if the main one fails, I can switch to the #2 battery and alternator with the flick of a switch.

    Hope this write up can still help and give you all some new ideas.

    I can also provide a wiring diagram of how my truck is setup, if anyone is interested in copying it.
    1988 Chevy Silverado 5.9L Cummins : 1968 Ford Mustang Pro-Touring

 

 
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