Delco-Remy 12SI

Here's a do it yourself tip to save some money.

You can rebuild your crapped out Delco alternator with basic mechanical skill, a few tools, a cheap rebuild kit, and these instructions. Here's how!

Ok, so your alternator went bad on you? You pop the hood and find the familiar and ubiquitous Delco Remy alternator found in scads of older cars from the 70's and 80's: Buicks, Cadillacs, Chevrolets, Pontiacs, Oldsmobiles, GMCs, Volvos, Saabs, Chryslers, AMCs, Jeeps...

If you like throwing your money away you can buy an alternator from the local parts store for $50+. Or, you can buy a $15 rebuild kit and fix it yourself!

This article describes step by step how to rebuild these alternators, based on a 12SI out of a 1986 Jeep Grand Wagoneer.

For more information on identifying alternators, this article by Mark Hamilton is very well done.

Parts and Tools

You can pick up Delco-Remy 12SI alternator rebuild kits for under $15 at any chain auto parts store or even online. Checker Auto Parts offers online ordering / in store pick up as well as online ordering. Here's some links to help you find the parts you'll need. Just click on the appropriate "Checker Auto Parts" link to go to the part specified.

Alternator	Kit P/N	Where/Link
56A, 78A, and 85A alternators	Victory Lap P/N GMA01	Checker Auto Parts
94A alternators	Victory Lap P/N GMA02	Checker Auto Parts

Note: just to be sure, you might want to click the "see all vehicles this product fits" link to make sure it will work with your vehicle.

Prepping for Surgery

You'll start by marking the housing so you know how the two halves are supposed to go together. These alternators can be set up to where the mounting bracket on the front half and the field plug on the back half can be oriented at any position. This is called "clocking" and is included in the part number. FSJs take a 9 O'Clock or 270* from the mounting bracket (on the top) -- which is the position of the field plug when looking at the front of the alternator. So, if you find a junkyard alternator and rebuild it, you can clock it to what you need for your vehicle.

The First Cut

Once you have it marked, go ahead and remove the four long hex head bolts that hold the two halves of the housing together using the right 1/4"-drive socket, extension, and ratchet wrench. Next, use a screw driver to pry the housing halves apart at the pry points shown and pull the case halves apart

Looking at Guts

Now that you've got yourself two halves of an alternator take the back half and stare into it and you should see something very similar to this, otherwise ... well, otherwise you're on your own.



See that white thing held in by 3 bolts in the pictures above? That is the voltage regulator. Also, you'll notice there's a black rectangular device with long silver contacts, held down by 4 bolts, 3 on one side and 1 on a long arm that contacts the voltage regulator. This device houses the rectifier diodes that turn alternating current into direct current. The regulator turns noisy direct current into relatively smooth, constant voltage. Finally, your brushes are those two rectangular black things held by a wire to a contact held to the regulator by a bolt as shown in Pic 1.

Pic 1. Brushes Pic 2. (L) regulator assembly, (R) housing that holds the brushes. Pic 3. Detail: retaining the brushes Pic 4. Detail: brushes held by wire, greased rear bearing, final regulator bolt

Note that there is something that looks like a threaded rod that is held down by two bolts that hold down the regulator and diode contact. Remember where this goes (fortunately you have these pictures to help). I am not sure but I think this is either a resistor or some other discrete component.

New Guts

So, go ahead and take out your regulator (Pic 2), brushes (Pic 1), brush housing (Pic 2), and diode assembly.

Your rebuild kit will provide you with new brushes, a new voltage regulator, new diode package, a couple springs for the brushes and a thin metal wire. Time to replace everything and reassemble.

The main trick is that you want to insert the correct brush springs (you'll have to compare and match the original springs to those available in your rebuild kit), and then hold the brushes in using that metal wire they give you, or a small hex wrench (Pic 3 & 4). There is a hole in the back of the alternator that you can use to pull the wire out, once you've reassembled. If you don't do this, the brushes pop out and you can't insert the shaft.

You'll also want to grease the bearing that is in the rear part of the back half housing (Pic 4). I just used hub grease.

Now, you toss the old diode, regulator, brushes. Take the new regulator and brush housing and put it back together and mount into the housing, using the bolt fastening the brush contacts in place as shown in pictures above.

Next, bolt the diode package into place with the three bolts first. Add the resistor threaded rod thingy, and bolt the final diode bolt into place. Now install the last bolt for the regulator (Pic 4).

Front Bushing

One thing I have not attempted is to replace the front bearing. However, I have had these go out before and they are included in the rebuild kit. It looks like it is a matter of using an impact wrench to remove the pulley and cooling fan, and then sliding the shaft out through the back of the housing. I also suspect that you would use a bearing/seal driver to punch the bearing out. I'll update this article when I get around to trying this. (Still haven't yet, sorry - 04/14/08)

I Just Saved a Bunch of Money...

So, now you're all done! You could've spent $60+ on a new alternator but instead, you just salvaged a perfectly good alternator for around $15 or less and an extra half hour's time. Unlike power steering pump rebuilds, this rebuild is difficult to get wrong.

If you do a lot of back country driving, the last thing you want is to have your alternator die on the trail so how about keeping a spare rebuild kit in your getcha-back-box? Or get a broken alternator from a friend for free and rebuild it as a spare.

Thanks, hope this article helps! If so, tell your friends

Feel free to contact me with any questions.

Copyright © 2008 by Michael Shimniok