SD22/SD25 Alternators and DPC Modules

Dealing with all subsystems specific to the diesel powered Datsun-Nissan 720 pickup trucks.

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waynosworld
Posts: 571
Joined: 11 years ago
Location: Vancouver Washington USA

SD22/SD25 Alternators and DPC Modules

#1

Post by waynosworld »

I have several of these alternators, what I notice is my glow plug light starts to act weird when I am going to lose or I have lost an alternator even though the charge light does not come on, the glow plug light only flashes instead of staying on until the glow plugs are warm, I have lost at least 3 or 4 alternators over the last 2 or 3 years this way, my first question is what is most likely the issue for these alternators to go bad this way(die slowly over a period of a few days), I pulled the cover of one of the bad alternators and pulled the brushes which looked great to me, I really do not want to spend hundreds of dollars having one rebuilt and I have no good extras anymore and the starters I have rebuilt only last a week, the solenoids they use are crap, I put a later model 3 blade type in this time only using two blades and it works fine.

Another question, after replacing the alternator my engine would not shut down with the key, I cycled the injection pump controller plug without any positive result, now when the alternator started acting up everything else worked fine, I tried a different DPC Module in case that was the reason the alternator was acting up and that was not it, but I wonder if doing that could have messed up that module, it moves to the shut down position if I use my finger to shut down the engine pushing on the arm, if I lose one of the fusible links it does not charge then either, but I think the charge light comes on when that happens, anyway I replaced the module and now everything works properly, so is there a wire/solder/connection that blew/melted in the DPC Module I can fix so the engine shuts down when I turn the key off?

I really like driving my 1969 Datsun 521 kingcab with the SD25 turbocharged diesel engine, but I hate replacing the alternators and starters, the fact is have to remove the alternator to remove/replace the starter as you can see in the photo, removing the alternator is a pain itself.
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Do you think heat might be the issue for the alternators going bad, the exit for the turbo is right above the alternator(about 4"), making a heat shield for that is not going to be easy and air does get in there, but it has to go thru the radiator first, there are all sorts of wires/hoses in that area, the power brake vacuum hose, the turbo oil feed line, the turbo oil return line to the block, the alternator vacuum oil feed line, the starter cable, the block warmer plug-in wire, the alternator wires, there is a lot of stuff in the left front engine compartment, the right front is just as bad, I have to remove the diesel filter housing to remove/replace the oil filter, that I got all this stuff in there and had it work properly was a feat itself, but it was done one thing at a time.

Also is there an easy fix for the alternator belt, when the engine is first started there is a lot of drag from the alternator to the belt and it squeals sometimes, once it starts charging there is less drag and it quits squealing, but to get the alternator adjustment bracket off to lengthen the adjustment even half an inch will likely require me to remove the radiator/fan/pulley, I have seen others lengthen that bracket but that long bolt hits the pulley before it comes out of the hole, nothing was/is easy on this truck, but it is my favorite vehicle to drive.
I know the voices are not real,
but they have some really good ideas.
plenzen
Posts: 890
Joined: 16 years ago
Location: Cochrane Alberta Canada

Re: SD22/SD25 Alternators and DPC Modules

#2

Post by plenzen »

What is failing in the alternator(s) ? Are the diodes burning out or is it just baked inside from maybe running full load, like the regulator is stuck ?
I had some issues a while ago with a Chrysler doing that and it was quiet enough I could hear the alternator screaming like it was under full load.
Baked it good.!! Figured it was just it's time and put a rebuilt on it, Worked for a few months and then same thing. Traced it down to poor ground between engine, chassis, battery etc. Cleaned up the chassis grounds, put a heavy ground wire. (10 ga) from the alternator bracket to the cleaned up chassis ground and it's been fine for a few years now. Just wondering is all.

That's pretty tight engine room you have there for sure. Lot's of stuff going on. Even a piece of aluminium dryer vent tube with a couple washers for spacers hosed clamped around the closest part of the pipe would help ?

I think it was Al or maybe someone on here years ago swapped to a Motorola 120 Amp ?? alternator and ran a separate 12v vacuum pump for the booster. Had a juice can reservoir and pressure switch mounted someplace.
That said, you don't appear to have any room for anything more under there, although the pump, reservoir etc could be remotely placed ?????? somewhere.

I know the down pipe on my SD25 ( natural ) has a heat shield all the way from the flange to where it turns under the fire wall. It's a2 piece aluminum with a hose type clamp at the top holding it to the pipe.

Dang Mr. That appears to be a "Project" to dig any of that out of there.
Retired Pauly
Problem with being retired is that you never get a day off.
1987 D21-J SD25 KC
KJLGD21FN
waynosworld
Posts: 571
Joined: 11 years ago
Location: Vancouver Washington USA

Re: SD22/SD25 Alternators and DPC Modules

#3

Post by waynosworld »

It does not even have the heat shield between the turbocharger and master brake cylinder reservoirs in that photo, I was still using ABS tubing when that photo was taken also, I really do not like working in the engine bay anymore unless it is something simple, starters and alternators are on my hate to do that list now.
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My stock head pipes with heat shields do not exist anymore with the turbocharger, made my own heat shield for the head pipe near the starter to try and keep the starter solenoid cool, but the rebuilt ones only last a week before I get clicks 50 percent of the time, if I hit my power bypass button/relay to the starter motor it usually starts right up without letting off the key in the start position, I would cut a giant hole in the inner fender but the steering column is in the way, it has just got old recently, this last alternator did not last long and I am out of functioning good ones now, I pulled the brushes out of one that did not work(tested by me on my test stand), the brushes were over an inch long, they looked great, I do not know where the diodes are or what good ones look like, but I am willing to take them apart and make good ones if I can out of parts from other alternators, I have about 7 of them now that do not work properly.

They either quit all at once(I think I have seen it die this way once) or they slowly die without the charge light coming on, I can tell when it is happening the slow way as the glow light flashes instead of staying on like normal, it still works properly(glow circuit) as I wait till I hear the click before starting it, but the volt meter shows less and less charge until it shows 12 volts, yet the charge light still does not come on, it is weird.

I understand the starter issues, but the alternator issues I do not understand unless it has something to do with heat, I have no room to route air in that area with a dryer tube, there is no room left for anything else, my radiator over flow reservoir is between the radiator and alternator, to the right in that photo above is the headlight section, I had to kind of hammer that area towards the fender on both sides to make room for the Volvo cross flow radiator as the modified Datsun radiator could not handle the heat with the turbocharger involved, that radiator was made for a 1600cc engine, the one I used before the turbocharger was for a 1300cc engine as it had the outlets in the right spots, but the turbocharger changed things, the 1600cc radiator worked for a little while but in the end it was not keeping up, I had the Volvo wagon radiator so I made that fit.

Over the next few days I will take a diesel alternator apart and see if I can find out what is wrong, I have one that the output post is gone, maybe that one has good diodes although I do not know what good diodes look like, where they are, nor do I know how to test them, I have never taken an alternator apart before, it is not something that goes bad that often in Datsun/Nissan gas trucks, I do have a lot of gas and diesel alternators though, all of them testing bad now, electrical components are a mystery to me, I have as many diesel starters around here also, but the inventory of good ones are getting low also, some sound good/test good until they need to turn the engine over, then they turn slowly, I have a different place for bad ones, good ones are in bins or on the good shelf.
I know the voices are not real,
but they have some really good ideas.
waynosworld
Posts: 571
Joined: 11 years ago
Location: Vancouver Washington USA

Re: SD22/SD25 Alternators and DPC Modules

#4

Post by waynosworld »

I pulled a couple alternators apart yesterday, I just do not understand them, I suppose I should have tested each one before pulling them apart to see if the light worked first as after pulling a few apart and putting them back together as none of the lights worked after that.

The first one I pulled apart looked completely smoked, sorry the photo did not focus that well but the plate looked burnt and it had what I would describe as ash between the upper plate and the lower plate, are these plates the diodes?
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I looked at the brushes first, some were longer and some were shorter, but none were short, I tested them and all had connections(continuity?), there is a small flat/shallow box under the brush holder, they all looked fine(not discolored or burnt), I put together two out of good looking parts but the light(dash light) never came on so I did not test them, I made a test stand.

I am beginning to understand why some old timers use normal alternators and install a belt driven vacuum pump, it is a hassle to deal with the stock alternator when turbos are involved, that is what Knucklehead did as I talked to him on the phone a few years ago when he was selling a turbocharged SD22 engine on the local craigslist, we talked for a awhile and he is the one that said something that made me think of the way I did my turbocharger install successfully, I was asking him about the draw thru setup I was working on and why it was running so lean and he said something about the vacuum line and a valve and it worked(made it run richer), so I thought if that worked would this other blow thru way work and it did, he made my brain think of it differently.

Does anyone know if a bridge(connection) of some type in the DPC Module goes bad/gets burnt that makes the engine not turn off/shut down when the key is turned off, the injection pump controller does move to the off position when I manually shut down the engine, meaning after I move the injection pump arm to the off position with my finger, the IP controller moves to the off position just after the engine quit turning, can I repair this by soldering the lost connection back together?
I know the voices are not real,
but they have some really good ideas.
plenzen
Posts: 890
Joined: 16 years ago
Location: Cochrane Alberta Canada

Re: SD22/SD25 Alternators and DPC Modules

#5

Post by plenzen »

Al is the guru on this kind of thing, its a bit beyond my wheel house. That said, the alternator that I roaseted on that Chrysler looked similar, probably worse even. Something caused (we think) the regulator to call for full beans and cooked it. We think it was bad ground. When I say
"we" I mean the alternator rebuild guy and myself. Anyway, as mentioned, I cleaned up the chassis grounds, and put a ground wire from alternator mounting bracket to the body and its been goid since.
However
Al may have some further insight.
Heat may still be an issue.

Sorry I don't have anything more useful.
Retired Pauly
Problem with being retired is that you never get a day off.
1987 D21-J SD25 KC
KJLGD21FN
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asavage
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Re: SD22/SD25 Alternators and DPC Modules

#6

Post by asavage »

Diodes. Diodes blow apart (but the potting keeps them looking like they're still in one piece) on the Hitachi LR150. And the VR will often get taken out by the bad diodes, so you change 'em both. I've been into a LOT of 'em.

Read all four pages here: viewtopic.php?t=799 . I bet I still have that homemade alternator test jig that was powered by my Craftsman table saw motor (I still have that saw . . . in storage, no room at home :( ).

I'm sure the part Nos. have gone NLA, but you can steal the diode packs out of other Nissans of that era, and you can use the LR160 rotor & stator from a diesel Maxima to get 10 more amps.

I had boxes and boxes of LR150/LR160 parts, but all have been gone for over a decade . . .
Regards,
Al S.

1982 Maxima diesel wagon, 2nd & 4th owner, 165k miles, rusty & burgundy/grey. Purchased 1996, SOLD 16Feb10
1983 Maxima diesel wagon, 199k miles, rusty, light yellow/light brown. SOLD 14Jul07
1981 720 SD22 (scrapped 04Sep07)
1983 Sentra CD17, 255k, bought 06Jul08, gave it away 22Jun10.
waynosworld
Posts: 571
Joined: 11 years ago
Location: Vancouver Washington USA

Re: SD22/SD25 Alternators and DPC Modules

#7

Post by waynosworld »

I searched diodes which likely did not help me much, but it did say they were connected to the windings, so I suspect they are on/in that plate I posted a photo of in post #4, I really do not know a lot about alternators, as of a day or two ago I have never had one apart before, that plate in the photo is the only one of the 3 I took apart that showed that type of damage, the rest I pulled apart that plate looked fine yet they do not function properly, only one alternator had medium/short brushes.

A long time ago I heard that generators needed to be basically shorted out once to work properly, they had a name for that process, yet it does not come to mind right now, is that something that needs to be done on alternators?

I made my own tester also, I used an old Wards Magma bandsaw(1950s?), I still use it to this day, it's a bit noisy but makes cuts without wandering, I just put an alternator mount on the lower shelf and use the drive pulley for the bandsaw on the motor to make it turn fast enough, the only thing I do differently than a stock wiring harness is grab power to excite the alternator from the output post going to the battery, kinda like a 1 wire alternator, but I wire in a light to see if the alternator is working instead of using a volt meter, if the light goes out the alternator is working, if the light does not come on I assume the alternator is bad, I suppose I could be wrong on this assumption and the only way to know for sure it is not working is to use a volt meter, but I tension the belt with one hand and turn the switch on and off with the other hand and watch the light, maybe I could wire a volt gauge on/in the tester, it would not be that hard to do.

The alternator appears to be putting out 14/15 volts when the engine is running, I am using my volt meter/gauge to gauge this, the gauge goes up to 18 volts, it is not putting out any more than any other alternator I have used in the past, but it is higher than what the last one was putting out at the end, by the way the charge light never came on when this last one died, it does come on using this alternator before I start the engine, I had been watching the volt meter get lower and lower as time went by, but when the starter slowed down that last time it started I decided it might not start again so I pulled the 520 out and parked this truck in its place and drove that one until I fixed this issue which took a while because that morning all 3 of my trucks had issues, brake issue on the 520, and two different issues on the work truck, I needed to get the work truck fixed first, then the brakes on the 520, both were easy to deal with compared to this truck, fact is the brake rear brake issue on the 520 has been an issue for a decade, it had the wrong wheel cylinder on the drivers side but it never puked brake fluid till that day, it just acted slightly weird when first driven for the day, now it works perfect every time I drive it, so it was worth the effort.

I will wire in a Nissan volt meter as I have lots of extras, and retest the alternators that have no light when wired into the test stand, maybe only the light circuit is the issue in a couple of them.
I know the voices are not real,
but they have some really good ideas.
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asavage
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Re: SD22/SD25 Alternators and DPC Modules

#8

Post by asavage »

"Flashing the field" is the phrase you're recalling about installing a generator after having been disconnected for a long time. Applying power to the field coil momentarily, to reestablish some residual magnetism. Older generators needed that (new generators do not, because they're almost never generators, but alternators in disguise).

The six diodes are welded to the c-shaped plates and then potted in a silicone. Six stator wires are soldered to them. On the Hitachis, you replace the the whole diode assembly as a single piece.

[Early Delco alternators, around 1964 through around '72, the diodes were pressed into their heat sink, and I used to created positive-ground alternators for use in my Hillmans, by pressing out the diodes and reinstalling them in reversed locations. The mechanical voltage regulators back then didn't care about polarity, and it all worked fine :)

Those early Delcos were 35A.]
Regards,
Al S.

1982 Maxima diesel wagon, 2nd & 4th owner, 165k miles, rusty & burgundy/grey. Purchased 1996, SOLD 16Feb10
1983 Maxima diesel wagon, 199k miles, rusty, light yellow/light brown. SOLD 14Jul07
1981 720 SD22 (scrapped 04Sep07)
1983 Sentra CD17, 255k, bought 06Jul08, gave it away 22Jun10.
waynosworld
Posts: 571
Joined: 11 years ago
Location: Vancouver Washington USA

Re: SD22/SD25 Alternators and DPC Modules

#9

Post by waynosworld »

asavage wrote: 11 months ago "Flashing the field" is the phrase you're recalling about installing a generator after having been disconnected for a long time. Applying power to the field coil momentarily, to reestablish some residual magnetism. Older generators needed that (new generators do not, because they're almost never generators, but alternators in disguise).

The six diodes are welded to the c-shaped plates and then potted in a silicone. Six stator wires are soldered to them. On the Hitachis, you replace the the whole diode assembly as a single piece.

[Early Delco alternators, around 1964 through around '72, the diodes were pressed into their heat sink, and I used to created positive-ground alternators for use in my Hillmans, by pressing out the diodes and reinstalling them in reversed locations. The mechanical voltage regulators back then didn't care about polarity, and it all worked fine :)

Those early Delcos were 35A.]
I actually have a couple of them Delco alternators in my alternator tub, and this just made me realize I did not check to see if I had any diesel alternators in that tub, thankyou for reminding me about that tub, now I have to remember to look in there. :lol:
I know the voices are not real,
but they have some really good ideas.
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