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How To: Chevy 105amp 3wire Alternator Swap

Last Updated: Feb 24, 2015
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mjavy7 avatar
mjavy7   +1y
Ok ppl. I finally got it to work witout a squel.
1993 b2600i. I ended up using a Durslast belt part number 15405. I hope this helps the 2600i people out there.
kam avatar
kam   +1y
Howdy All,
Been gone for a while, haven't had my truck so I haven't been doing much until now. Drove her from STL to Cleveland, made it just fine with the exception of a front wheel bearing going out in the last 50 miles. (Replaced with Timiken, bearing turned out to be original w/ 235,000 miles on it. -- oh well)

Anyway, more to the point. I followed these instructions (with some modifications of my own) For a B2600i pickup. The swap is relatively similar with a few key differences to note:

For one, the m10 x 80 bolt is too short. B2600s use a drill block and a sliding bracket for the alternator adjustment instead of just a bracket. For the 2600, both the block and the bracket need to be reamed out.

Drill bits I used were 13/32 for a tighter fit, could go to 27/64 for a little looser feel.
Bolt I used was a 3/8ths inch (VERY SIMILAR TO M10) with coarse Threads, 4 Inches long. (need to compensate length because of the block). Instead of using a dremel to adjust the bracket, all I needed was a flat file, however there was some serious filing involved.

The upper bracket for the B2600 needed to be taken off completely, and given a small (one or two washer) shim away from the engine to fit right with the GM unit. Don't go more than this or else thhe bolt isn't threaded into the block right. If you need more shim, I suggest you bend the bracket, or get a longer bolt into the block (Which I intend on doing soon)

Also, the lower bracket on the B2600 is slightly different, I had to file the outer casing of my alternator a little and adjust the drilled out hole to be a little looser (27/64ths) so that it would fit on all the way.

Do Note: I noticed that the fan on the GM unit comes VERY close to the horizontal bracket of the 2600. For me, it seems to clear the bracket with about 3mm to spare, however I strongly recommend that anyone doing this swap check to make sure none of their alternator blades are bent out or are too long. The tolerance is a little tight, and I sure wouldn't want to see anyone whacking their alternator blades off into their engine doing this.

Other than that, the retrofitting is roughly the same. The original alternator is still the mitsubitchie 55 amp unit, with the same two wire connector on the back. My findings were that White/red Stripe was 12 Volt constant, White/Black Stripe was with ignition.

Oh, and if you are wondering. The alternator I used was from an 83 Citation, I made it work, however I noticed that unlike the one used above, this one had the connector near the back of the alternator, right in line with the hole for the lower tab. I made this work OK with a small ammount of difficulty, however for future ease of use: TRY TO FIND A GM ALTERNATOR WITH THE CONNECTOR NOT IN LINE WITH THE BOLT.

Final words: It seems that the GM units want to be spun a little faster than the Mitsu. I haven't had any problems yet, however I am only getting 12.3 at idle, 14v comes at around 2000-2500 rpm. Any suggestions?
Oh and the Duralast Belt mentioned is a *litttle* short, but its okay. Works well.

Pictures of stuff below:

The drill Block
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The Horizontal Bracket
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Choose Alternators Wisely: DO NOT LET THIS HAPPEN TO YOU
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Reamed and Filed so it can go around the B2600i lower bracket nice and smooth. (Stupid cast iron parting lines...)
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Fitting it in: NOTE SHIM WASHERS
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All fitted in nice: note close fit between blades and bracket. Just be careful.
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dealwithit avatar
dealwithit   +1y
if you want abit more power than the gm 105 amp unit, the ford 3g 130amp (there are lots of different ones, but certain ones have the same mounting tab setup as the gm unit) which is usually on 90's taurus, windstar, mercury sable, and a few others im sure (and all these domestic fwd cars are littering the junkyards everywhere). the install is pretty much the same except for the wiring. the key to the ford 3g alt install is that the keyed power needs a resistor installed inline before the alt (at a value of around 500ohms, a 1/4w to 1/2w electronics resistor works just fine, they're cheap and available at most electronics stores) or they wont turn on and charge. they all came with serpentine pulleys on them, but its easy enough to switch the mazda v belt pulley onto it (be careful tho, 130amps is right at the maximum a v belt can transfer, Hp wise, if its not quite tight it will squeal under heavy load).

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i did this swap into a previous b2200 i used to own, and my current project truck already had one when i got it. heres my swap thread

you can also get a 1 wire regulator for these just like the gm if you want to make the install even more simple, but the resistor is going to be alot cheaper with the factory regulator. cheers
coloradolowlife avatar
coloradolowlife   +1y
So i found out today that a b2600i (g6) takes a 7420 gates belt if you have power steering and do the gm mod...

ok my bad...bad was too a #7405 ends up being just right 40ish" by 10mm

this is for a 91 b2600i with a g6 engine w/power steering