Rebuilding a Land Rover alternator 
Text and photos by Peter Matusov

This story began a few years ago, before the majority of my vehicles achieved junkyard candidate status.

If you're like me, every corner of your garage is taken by one or another Jeep or Land Rover part that you removed from your vehicle in hopes of future rebuild, or to chuck as a core in a parts store when another one bites the dust, or an already stashed replacement.

Chances are, that part is an alternator. In my case, when we sold the house and bought another, and moved the stuff to the new one, I found FOUR Land Rover alternators, of not quite clear provenance or in not quite clear working condition. One of them was lovingly rebuilt by Automotive Exchange and Supply in San Diego, three remaining were core candidates.

Every time I am about to chuck one in the trash bin, I picture a face of some poor kid far away, winding these coils in the dim overhead light, for not even a drink a day. Since I am not currently in the need of a working alternator (picture this, in 5 Land Rovers in the immediate and 3 more - in the extended family), I decide to just rebuild one, or two, or all of them.

In the old past, I have rebuilt Bosch - and with lesser success, Lucas - alternators; this time the pile was composed mostly by Magneti Marelli units, used in 1995 Range Rover Classics, 1994-1999 Land Rovery Discovery, and in 1995-1999 P38A Range Rovers. Most of them were not-quite-dead-but-getting-there units, resulting in intermittent tachometer reading dropouts and unexpected hard starting in the morning. Most of them was subjected to extensive fine dust ingestion from trips to Utah and Death Valley, so it was natural to expect that the brushes should be the first thing to go.

Popped the back cover on one of them, and saw the integral voltage regulator/brush holder unit. Just like Bosch, I thought.

Finding a replacement online turned out less than easy, and not entirely successful. British Parts of Utah had a unit in stock, and it found its way to my doorstep a few days later. Down in the garage, I popped the plastic back cover, and proceeded to unscrew the old, ugly, and crusty, regulator. For whatever it's worth, you'll need an assortment of small metric nut drivers (including 5.5 mm), and a couple of Philips screwdrivers of different sizes.

After nearly stripping the nears of three screws that keep the regulator to the back cover of the alternator, I finally got the old one out. Time for the new, shiny, and beautiful, one to get back in.

WTF... The fat positive terminal on the rectifier assembly would not fit through the hole. And the rest of it doesn't quite fit.

I realized that I ordered and received a wrong part, and tossed both in the pile on the workbench.

At some point later, the tachometer needle dropped to zero on my 1996 Discovery, fittingly at the tail end of a trip to Death Valley - so I knew instantly the rebuild is back on schedule. But how come I had a wrong part?

Another Google search revealed a multitude of alternators Land Rover used in the same time span. The V-belt Range Rovers in 1994 used the old A-127 Lucas unit, while serpentine-belt Discovery in 1994 used - likely - a 100-Amp AMR3107 unit. Or was it a 100-Amp AMR4247, which was also used on early P38A Range Rovers? My situation was somewhat complicated by my use, over the years, of 120-Amp P38A alternators on my 1995 Classics and 1996 Discoveries. I know for a fact that at least two of them have a factory sticker on the side, proclaiming them to be 120A units, with part number AMR4247.

To further confuse the nomenclature, Land Rover Direct would sell you a part with this brief description: "Alternator A127 120amp part number AMR2938. This fits the Range Rover P38 V8 Efi engine."

Here's a photo of two alternators of very different vintage and provenance. To Land Rover's credit, both would physically fit and be electrically functional. Guess which is which?

Two alternators

To make our life even more exciting, this sticker - still attached to the unit on the left in previous photo - lists not one, but THREE part numbers: A127, AMR4247, and (Magneti Marelli proprietary) 63321353.

Two alternators


It took quite a bit more Googling to discover a wonderful world of seemingly-interchangeable, almost-the-same, alternators made by Magneti Marelli, Bosch, Denso, and God knows who else. But, fortunately, most of them use one of two types of voltage regulator/brush holder units.

An aftermarket supplier, Transpo, labelled them IX123 and IX128, respectively. When I had them all at hand, I took a picture of the old regulator from my alternator, and two of these units.

Two types of voltage regulator/brush unit

At the photo above, the old unit that came from a 120A P38A alternator is at the left, the wrong IX128 - in the middle, and the correct replacement IX123 - on the right. Ignoring the removable brush cover on the IX128, you can see that they are not interchangeable.

At the time when I found and purchased a correct one, I stuffed it in one alternator from my stash, wrote "Good" on the side with a Sharpie, and put under the workbench without bothering to test it.

Fast forward a few months.

A regulator failed in my brother's 1996 Discovery (which I owned earlier), and I felt obligated to get him back on the road - so he came over and we quickly swapped in the shiny rebuilt alternator.

A couple of months later, my brother comes back with a really loud roar from the engine compartment, correctly identified as failed bearing in the rebuilt alternator. We yank it out, and put one together that seems to work.

We also disassemble the shiny rebuild, and find that the ONLY telltale signs of anyone ever working on this alternator are the bad solder joints between the stator coil wires and rectifier assembly.

Automotive Exchange and Supply did NOT bother to replace any other parts. The alternator had an old-style regulator unit and - out of rebuild!!! - worn next to nothing brushes, and either badly worn out or incorrect rear rotor bearing.

A further inquiry discovered that this place is even worse than Meridian in San Diego - at least Meridian manages to maintain about 50-66% of "working out of the box" rate for their power steering boxes. So much for farming that out.

Time for another Google search.

This time, it unearths a fantastic source: Maniac Electric Motors. Among a million other things, these guys would sell you anything from a complete alternator to parts and kits to rebuild one, including the regulator/brush unit, front and rear bearings, slip ring, brushes, rear cover, and whatnot.

By the way, this kit, according to ManiacElectricMotors, fit a variety of alternators - including "Land Rover AMR3021, AMR3107, AMR4247 Marelli 063341353010, 54022543, 63321353, 63341353." So... Are you telling me that IX123 fits AMR3107? Because I have an AMR3107 unit using an IX128 regulator, right here on my workbench... In any case, it will likely work for a Discovery 100A alternator, or 120A unit from a P38A.

I just had to try it. This is what comes in the kit:

ManiacMotors rebuild kit

OK, rant over: time for work.

Disclaimer: this procedure applies to AMR2938 (A127?) alternators, but AMR4247 and other Marelli units should be similar.

Step 1: remove the alternator from a vehicle (if it hasn't been done yet). For a serpentine-belt 1995 Range Rover Classic or 1994-1999 Discovery 1, it involves four tools and a bit of fiddling. In brief:


Range Rover Classic and Discovery Series 1 alternators use 67-mm diameter pulleys, so if you are tempted to swap in a P38A unit, keep the proper pulley.
Back cover of the alternator

Step 2: disassemble the alternator.

This is a picture of rectifier diode assembly removed from the back cover of the alternator. Note one missing diode and unused terminal - this is a rectifier from a 100-Amp unit, the 120-Amp unit will likely have four diodes - and four stator wires to disconnect from the assembly.

Rectifier: one missing diode would be used in 120A AMR2938 unit.

Since we're here and have the rectifier assembly out in the open, it would be prudent to check with an ohmmeter or diode tester to make sure the diodes are okay.

It is helpful to associate the rectifier terminals with their functions; the picture below shows which wires go where. The pair of diodes shown gray and "wired" to an unused terminal with an orange line is present in 120A alternators.

Rectifier: one missing diode would be used in 120A AMR2938 unit.

To check a diode with an ohmmeter or diode tester, the positive lead should be connected to the anode of a diode (a triangular arrow part on the schematic), and negative - to the cathode (a cross-bar at the tip of the arrow). If the diode is not burnt out, the ohmmeter should show resistance, and diode tester should show some voltage drop (about 0.5V for non-Schottky diodes). Now, connect the ohmmeter leads in reverse order to a diode - it should show infinite resistance (no continuity). If the reverse resistance if not infinite or there is a rather small voltage drop in reverse direction, the diode is blown and has an internal short.

To apply this esoteric knowledge to the rectifier assembly at hand, the following has to check out:

Positive Lead goes to Negative Lead goes to Voltage drop Continuity If not, what failed
+ (8mm stud) G (ground, back side of rectifier) Unknown Absent One or more diodes shorted
G (ground, back side of rectifier) + (8mm stud) 1.0-1.4V Present Three or more diodes burnt out
+ (8mm stud) A, B, or C Unknown Absent Top-side A, B, or C, diode shorted
A, B, or C + (8mm stud) 0.5-0.7V Present Top-side A, B, or C, diode burnt out
G (ground, back side of rectifier) A, B, or C 0.5-0.7V Present Bottom A, B, or C, diode burnt out
A, B, or C G (ground, back side of rectifier) Unknown Absent Bottom A, B, or C, diode shorted

If you find an issue with any of the diodes, you can go ballistic and replace the one that died. I would rather replace the entire assembly - it's only about $20, give or take.

This is the back cover of the alternator, with stator coil wires protruding via insulating sleeves, and rotor slip ring visible in the middle.

Here you see the front and back halves of the alternator separated.

Assuming you have taken off the pulley -

Note that this can be done even if you have not managed to remove the pulley, but it would be annoying to have to do it all again if the front bearing fails soon after.

This is the bottom of the front half of the alternator housing with the bearing removed.
These are the old (right) and new (left) 6303 bearings side by side. The difference in size is only due to oblique angle of the photo.
Step 3: reassemble the alternator.

I love the last item. It took me close to an hour, and two ruined replacement slip rings to achieve that.

Let me elaborate.

That may end up being a complete destruction of the old slip ring. In my case, the base of the slip ring was glued to the rotor - not with epoxy but some sort of hard and brittle glue. The slip ring itself - the cylindrical part with two copper rings - sits very tightly on the shaft, and two plastic "legs" (that also serve as insulators for the conductors from the copper rings to the terminals) may also be tight in their grooves. After ruining two of them, I resorted to the shaving a little material off the plastic "legs," and very gently tapping the last remaining slip ring onto the rotor shaft, occasionally applying gentle pressure onto the base so the "legs" don't buckle - yet they don't get separated, either!

I also soldered them onto the terminals, using 95/5 tin/antimony solder with melting temperature of 240C (464F).

Back to the back half of the alternator housing:

The last will also test your dexterity and patience. When the rear housing is fitted and bolt holes matched, spin the rotor inside the housing to make sure the rotor does not interfere with the stator wiring - this is important.

Don't forget to remove either a wire or a plastic cover keeping the brushes depressed in their openings; otherwise you'll be wondering how come you have a dead alternator with all new and shiny parts. Been there, done that...

Lo and behold...

For whatever it's worth - O'Reilly can only test the alternator in YOUR vehicle, and our local NAPA no longer even does it. Which leaves... bolting it on.

Step 4: install the alternator into the vehicle.


I really, really, hope that the last three items check out for you. Otherwise, you might be inclined to return to Step 1. Otherwise, proceed to

To me, one time the tachometer did not operate after an alternator rebuild - on a 1995 Range Rover Classic - and ended up being a tachometer issue. It took removal of the instrument cluster and replacement of tachometer with one poached from another cluster. But that's another sob story.

That is all.

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