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Alternator upgrade for older trucks

Discussion in 'Truck & Equipment Repair' started by greenshoes, Jan 24, 2011.

  1. greenshoes

    greenshoes Junior Member
    Messages: 3

    I need to upgrade alternators on two trucks.

    First truck 79 chevy, 3/4 ton, 350 eng, Dual batteries, headlights, stock stereo, heater blower.
    Second truck 85 chevy 3/4 ton 292 eng. Single bat. headlights, stock stereo, heater blower.

    Talk to a local shop that specializes in auto electrical work, but don't know what to make of his advice. I think he's just trying to clear out some stock.
    He said for both trucks a 93 amp alternator was good enough, and he has then in stock.

    I've read a lot of posts here on this subject and most people are upgrading to 200 amps, but most people posting here have new trucks.

    I would appreciate some advice for these older trucks. Thanks Greenshoes
  2. Rat_Power_78

    Rat_Power_78 Senior Member
    Messages: 175

    First off, put dual batteries on the second truck, unless you arent using it much. Sounds like he is recommending the same alt I asitched to on my 76 this year. I tried one of those supposed "100 amp" rebuild kits from jegs on a stock 10si case, but only got about 65-75 amps out of it. I ended up with a 12si (pretty sure Im getting these numbers right). It puts out 93 amps, and I believe the stock application was for a buick. Case size is the same where it counts (hole spacing) and it fit the stock brackets. Your stock alt on your 79 is no bigger than 63 amps, and this one will make a huge difference. Only other option would be to try to find a shop that can rebuild the stock one to put out more.
  3. sweetk30

    sweetk30 PlowSite.com Addict
    Messages: 1,588

    for my 90-95 style serpbelt on my small block i have one of there 200 amp alts. with single 900cca battery. i dont have electric plow but lots of power needs and biggest is lightbar at 60-70 amps all on.

    the dyno sheet with the new alt showed 125 amp at 800 rpm then 210 at above 2000 rmp.

    i have zero power problems now.

  4. dave_dj1

    dave_dj1 Senior Member
    from NY
    Messages: 350

    I'm not sure if it can be adapted but there are Ford alternators (that can be had from junkyards for 25-30 bucks) that are 135 amp. It's basicaly a one wire unit. Google search
    3g upgrade or check out Ford Truck Enthusiest website. I just did this to my old 79 F150 and man what a difference.(stock alt was only 60 amps) I have a Meyer 7.5' plow on it and some safety lights. I do need a larger battery now though as the one in it is a small car one.
  5. forbidden

    forbidden Senior Member
    Messages: 392

    Research high output alternators from people like Ohio Generator. Do not use a remanufactured alternator that has more windings in the same size case, it will leave you with grief. More winding, same case = more heat = quicker failure leaving you dead in the snowpile. Do not just add a second battery, it will not magically solve the issue. A second battery is another draw for the alternator to now supply, now it compounds the problem. If you are having current issues with one battery, how is two then going to help. 93 amp alternators? Don't touch them, not enough output even though your vehicles are devoid of current sucking devices like todays vehicles. Stock alternators were designed to run the vehicle with a little left over but not enough to properly run a snowplow + lighting etc.
    Last edited: Jan 26, 2011
  6. welded wrenches

    welded wrenches Senior Member
    Messages: 177

    special g.m. alternator

    hi there,,what is and true that works on them 73-87 k series chevy gmc trucks is fatory oem ones that are stamped on the alternator housing the embossed stamp reads 78 AMP these are rare..these are a special LOW RPM Hi-OUTPUT..These do put alot of amps just at idle rpm speed.Find and locate a private owned alternator-starter rebuild shop..that is well recommended for doing great repairs..You not find any of these at a parts store or in a magazine..and yes dual batterys.2 the same new 1,000 CCA Batterys..good luck to you...
  7. Dr Who

    Dr Who Senior Member
    Messages: 637

    Find a shop that rebuilds alternators and have them build you one. All they would have to do is take the guts for something like a caddy or other big Gm car that has tons of electrical stuff on it and put it in your housing.

    I had this done for a Grand Wagoneer, they made a alt for a Northstar Caddy fit the Wagoneer, just had to get a wire adapter kit from them and I was pushing about 190amps....

    I wish I did this for my ford, but I was in a spot and did not have time to have one built, yet!
  8. stonewellmark

    stonewellmark Member
    Messages: 41

    My 97 dodge cummins has a 120amp and have NEVER had a problem....I can run the hell out of the plow with no issues. It has 2 batteries, I would say add the 2nd bat. on the 1 truck and go with the local shops suggestions. Just my 2 cents.
  9. forbidden

    forbidden Senior Member
    Messages: 392

    My next question would be do you want to do it right and solve the problem or put a band aid on it and hope it works and who knows for how long.

    FACT - more windings in same size case = more heat = failure. Heat is a natural byproduct of the production of power. You have to get rid of the heat.
    FACT - adding another device like a battery to a electrical system that is already having problems = burned up alternator.

    FACT - make the supply of current as efficient as possible. The ground wire is the single most important wire in your vehicle. Here are some links to help you understand what you should look at doing first and foremost.

    This link is a must do for any vehicle that has a draw of current. While the demands of a high power stereo system are one thing, the same can also be said about plows, sanders, lighting circuits etc. The same rules apply.

    This link is about the importance of grounding. Instead of reading amplifier or stereo, substitute in plow or whatever electrical device is attached that is a major draw of current in the electrical system.