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Generation 1 Pajero NA - NG Models 1983 - 1991

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Old 24-12-19
Ryan175 Ryan175 is offline
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Join Date: Mar 2019
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Default Successful 2.6L Alternator Upgrade

So last week my factory alternator packed it in after 33 years of good service and I swapped it out for a 100 amp unit from a gu patrol and figured I'd do a write up in case anyone was interested.

I suspect it had been on its way out for a while as the voltage only went up to 13.3V at 3000rpm and it struggled a lot when I put some load on it. My second battery got accidentally very discharged and I didn't have my battery charger so I used my alternator to charge the battery up for an hour or so which I think is what finally broke it. Afterwards the alternator was drawing 4 Amps down the main charging wire, even with the key off so I suspect one of the diodes had died. Given I have a winch, dual batteries, light bar, spotties and air con, plus a fridge and a pie oven in the back, I wanted to upgrade from the 50A stock alternator.

One of my mates had a 100 Amp alternator out of his old gu patrol, rd28 motor and the pivot to foot spacing was the same as my alternator. only difference was the inside foot to foot distance was a bit longer and the alternator itself was a bit deeper. No vacuum pump on the rd28 alternator either so it was a pretty close match to the paj alternator. Also note the patrol alternator had the same number of connections and wiring type as the paj one, a charging wire, a voltage sense wire and the alternator light on the dash (which also does the excitation field I believe).

We pulled the old alternator out and compared it to the patrol one, the hole spacing and location was the same between the pivot and the adjuster (175mm). The patrol pulley appeared to line up as well when the front feet were aligned, the rear foot was about 30mm further back than the paj alternator's foot. The patrol alternator had a double pulley arrangement and the groove closest to the alternator was the one that looked like it would work. We found some spacers to pack out the extra gap for the rear pivot foot and then had to find a longer bolt as well. there's a hole in the block the alternator pivot mounts to, this hole is sized for I believe an M8 to go through, and we weren't able to get a drill to it so we had to find an M8 about 120mm long. this left some room around the bolt in the holes of the patrol alternator which I was going to pack out with some copper tube or something, however forgot and just put it in without and seems to be working fine. Also had to get a longer adjustment locking bolt as the patrol alternator had a thicker casting there.

With bolts sorted we moved on to wiring, the paj wiring uses a white cable running from the battery, through the main fuse and then down to the alternator. Supposedly able to handle 50 amps however to me it seemed a bit undersized. We needed to upgrade the wire to handle 100amps and still keep it protected by a fuse of some sort. didn't particularly want to blow the main fuse when i used the winch, so we capped the old charging wire where it attached to the alternator and wrapped it in electrical tape so it couldn't short, then ran a new thick cable from the alternator, through a 100 amp circuit breaker and to the battery. this way the car was still powered via the main fuse and the old charging cable, and the new charging cable was able to handle the 100 amps and still be protected.

The next one was the alternator light on the dash, from what I remember this comes from the battery, through the globe and then gets earthed through the alternator when the ignition is on, and when the alternator is running it increases the voltage on the alternator side so that there is no potential difference and the globe turns off. I bought a plug from repco that fit into the patrol alternator with 3" of 2 wires sticking out the back of it, red and white wires. we found a receiving plug in my mates box of wires for the original pajero alternator plug and then was able to splice them together to make a patch loom. the globe wire (white on pajero side) went to the white on the new plug, and the voltage sense wire (blue on pajero side) went to red on the new plug.

When we test fitted we found that the front groove in the double pulley of the alternator was interfering with the AC belt, so we pulled the pulley off and I cut the front groove off then ground the cut down to be as even as I could. Theres now about 5 or 10mm of clearance, just enough.

We bolted it all up and plugged it in, the plug is now also on the engine side, bit of a pain but you can get the plug in, just once you get it in it really doesn't want to come out. When we started it we found the alternator was putting out 15V and when driving was up to 15.5V. Ideal range 14-14.5V is what we were going for so this was a bit high. Did some checks and it turns out we were losing about 1V of Voltage drop in the voltage sense wire. Checked the patrol manual and that wire has a 7.5Amp fuse in the patrols so we suspected the tiny wire in the paj wasn't quite cutting it or there was a bad connection somewhere. I replaced the wire with a thicker gauge (around 15amp) wire run to my fuseboard with a 7.5amp fuse in it. started her up and the voltage was down to 14.3V - perfect.

I'm pretty happy with how it turned out, even with a fair bit of mucking around to get it to fit. Nothing too complex, just finding and fixing issues as we found them. Ideally I'd like to upgrade the circuit breaker to 120A or 150A because Idon't know if the alternator may put out a little over 100A at full load and when winching it would be nice to know the circuit breaker won't pop. I'd also get a boot and put it on the charging wire connection on the back of the alternator as my mate didn't have one, just to cover the high current 12v terminal a bit. I would've also like to cut the pulley on a lathe but didn't have the option at the time I was doing it so this worked as well. Other than that it seems to be working well, keeps the voltage up over 13V even with air con on and charging the second battery. I also like that the part is a lot more common now, I can walk into patrolapart or repco and they will most likely have one in stock, wehereas the paj stuff for the gen 1s is always a bit tricky to find. From what I've researched it seems like this swap is also possible with an alternator from a td42 patrol as well, just make sure it doesn't have a vacuum pump on the back either.

I'll upload some photos when I get a chance. I know the 50A alternators are a bit outdated and with the amount of appliances we have now days an upgrade is pretty much required. Hopefully this helps if anyone is looking to upgrade.
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1986 LWB 2.6, 31" AT BFGs, winch, UHF, 52" light bar and spotties, rear light bar, roof rack, awning, 2 jerry cans just to get anywhere
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Old 1 Week Ago
Ratbago Ratbago is offline
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Thanks for this write up mate , even though ill probably never end up doing it , its good to have this information for those who undertake this .
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Old 1 Week Ago
disco stu disco stu is offline
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Interesting reading about how you dealt with the electrical issues too. Nice work
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