Gen light on, repair or replace the alternator?

[TJ Hopland]

While driving the 73 today I noticed a slight glow from the GEN light.   Slightly odd thing is I have a volt meter and voltage was normal.   Guessing that means I have a diode out in the trio?   

Car is a 73 which originally had a 63 amp? 10si internal regulator alternator.   After burning through a few dozen of those when I first had the car I upgraded to a 76 amp 12si unit which was more common in the 80's, known for better cooling among other improvements.    Its been on there for maybe 15 trouble free years now with many of those years being very low miles.   

I think what killed it was yesterday I was running around pulling a trailer with the AC on.  Demand and temps were likely a little on the high side. 

Normally I would just replace it but being that I am currently in the more time than money club and the likely hood that most of the replacements will be a crap shoot at best for quality I was thinking of repairing it.    Looks like the 'trio' is available as its own part and is only $5-15.   Looks fairly universal and appears to fit just about all those family of alternators. 

I can't imagine that its that difficult of a job?   Its just something I have never done before.   Will I even need to use a press or will it come apart more or less by hand?  Any tips or tricks?   Isn't there brushes?   Usually a trick involved to work around those when they don't have external caps.

[The Tassie Devil(le)]

Have a look at the condition of the Brushes.

Might need a clean up of the Commutator (that round thing that the brushes ride on.)

Bruce.

[bcroe]

Those symptoms for me were caused by an open diode, either the 
trio or the main power.  A scope on the pins will show up as a missing
3rd ripple, or take it apart and check the diodes.  I would much rather
fix a well run piece, than trade it for possible junk from Asia.  Bruce Roe

[TJ Hopland]

Thats kinda what I was thinking.   The current one has road tested bearings that were maybe made in Mexico or Taiwan.   What I buy today won't likely roll as smooth out of the box.

I never actually looked at the internal schematic of one of these things before.    I see its a 3 phase generator with a full wave bridge so 6 power diodes.  That part makes sense,  standard AC to DC power supply.   What's the trio doing?   Looks like blocking diodes to each of the 3 outputs?    Are they letting DC to the stator to get things going or are they lettings some DC(ish) output to the regulator to keep it engaged ones its started?

[Cape Cod Fleetwood]

We'll assume the belt is tight and in good condition?
For $50, just bolt on another one and go back to enjoying your car.
MHO

https://www.rockauto.com/en/catalog/cadillac,1973,eldorado,8.2l+500cid+v8,1025873,electrical,alternator+/+generator,2412

[TJ Hopland]

I know I can get a replacement just not sure I trust the quality.   I looked and can get one locally today for about what getting one online would cost if you include shipping.     Since I know that is an option I may just take it apart and see what I see.   I can also get the internal parts locally.   Another slight possibility is I have a larger unit out of a diesel that may or may not fit that may or may not be good that may or may not get be going again while I screw around with the others.   My job and industry is practically dead with no signs of a return anytime soon so I have the time.

I did figure out what my 12si upgrade 'came from'.   84 Cimmaron.   So if anyone wants a slight upgrade for the original internal regulated unit that's what to ask for.    Direct bolt and connect up except the rear bolt doesn't align so it can't be used.  Hasn't seemed to cause any issues not having it there.   Biggest difference visually is its got an enclosed fan.  Its still behind the pulley but the blades are not open like the earlier ones.   That was apparently one of the cooling improvements between the 10si and 12si series.   

[Daryl Chesterman]

TJ, you might find this Delco Remy Service Bulletin of interest.  It is for the 10si, 15si, and 27si, but the 10si and 12si are basically the same other than some minor structural differences and their output, of course.  It talks about the theory of operation, trouble shooting, disassembly, testing of components, and reassembly.

http://www.gmcmhphotos.com/photos/data/6522/Delco_Alternator.pdf

There are also some You Tube videos that show similar information, but like many You Tube videos, some are lacking in quality of information and thoroughness.  I just Googled "Rebuilding a Delco 12si alternator".

I have rebuilt a 10si, and it isn't hard at all.  If you think you might not remember how to reassemble, just take detailed pictures as you disassemble the unit.  Just a few cautions that are not noted in the above article.
     1.  Mark the two housing halvesâ€"I used a center punch to place a light mark on the boss above one of the
          4 housing assembly boltsâ€"some people use a permanent marker or a scratch awl.  This keep the same
          clocking of the rear housing when you reassemble it.
     2.  When separating the two housing halves, be sure the stator stays with the end frame assembly as you
          separate the two halves or you will break the three wires of the stator.  The instructions say to put tape
          over the needle bearing to keep dirt and foreign material out of the bearing, but in my experience doing
          this will be more likely to knock dirt into the bearing.
     3.  To remove the nut holding the pulley to the rotor, place the rotor in a vice, as they suggest, and use
          an impact wrench (electric or air).  Take note of any spacer bushings that may be present behind the
          pulley.   
     4.  I would recommend replacing the drive end frame bearing, as it is the one that takes the most abuse.
          You don't have to use a press to install a new bearing, but it is better than driving in a new bearing, as
          you have smoother control of the installation.  Whether using a press, or driving in the bearing, I use a
          socket of appropriate diameter such that you are only pressing on the outer race of the bearing.  The
          Delco instructions talk about adding grease to the bearing if reusing, but you will probably find that the
          bearing is sealed on both sides, and adding grease is unnecessary.
     5.  When removing the three screws holding the brush holder and voltage regulator, take note of the
          position of the screws with the insulating washer under their head.  Inspect these insulating washers
          to be sure they are not cracked or otherwise compromised.
     6.  If you need to replace the needle bearing in the end frame, support the housing from the inside with
          a pipe of sufficient diameter to allow the needle bearing to pass through it.  This will prevent the
          possible warping or breaking of the housing if the needle bearing is a bit difficult to press (or drive) out.
     7.  When replacing the brushes (or reusing the old ones), have available a straightened paper clip, or a
          small diameter drill bit, place the springs in the brush holder, and then place the back side of the brush
          against the spring and press it into the holder far enough to place the drill bit or straightened paper
          clip through the hole in the brush holder past the face of the brush and do likewise with the second
          brush.

Good luck with your trouble shooting and rebuild.

Daryl Chesterman

           
         

[bcroe]

I never actually looked at the internal schematic of one of these things before.    I see its a 3 phase generator with a full wave bridge so 6 power diodes.  That part makes sense,  standard AC to DC power supply.   What's the trio doing?   Looks like blocking diodes to each of the 3 outputs?    Are they letting DC to the stator to get things going or are they lettings some DC(ish) output to the regulator to keep it engaged ones its started? 

The way it is supposed to work, the GEN light and maybe some resistors
start supplying a bit of current to the rotating field.  That lights the light
at less than full batt.  As generation begins, most current flows through
the 6 main diodes to battery, which limits just how high the voltage will
go.  Some current goes through the small trio, bringing up voltage at
GEN to batt on both sides, it goes out.  Sometimes drop in high
resistance wiring will cause the lamp to glow a little. 

With full batt available from the trio, it takes over running the alt. 

If a main rectifier diode opens, one of the 3 pulses of current to the
batt will stop.  This causes marginal alt output.  This can be seen as
one of 3 ripples in output voltage will be gone, very big if you have
a current probe for your scope.  When the coils pass the missing
phase, coil voltage will not be clamped by batt, and will spike up. 
This spike will go back and start to light GEN. 

If a trio diode is open, voltage to the field will not be constantly
maintained.  As that phase goes by, the voltage drop will start to
light GEN as it does before startup. 

I replace bearings and brushes on a regular maintenance basis. 
I do not change long running diodes unless they fail (the
replacement could be poorer than the original).  good luck,
Bruce Roe

[savemy67]

Hello TJ,

Below is a link to my restoration thread on this forum.  Scroll to replies 73 and 74 to read about my alternator rebuild.  Yours should be similar.

http://forums.cadillaclasalleclub.org/index.php?topic=133691.60

Respectfully submitted,

Christopher Winter

[TJ Hopland]

Short version..... fail, but I know know how they are put together. 

The one I had laying around in unknown condition was a 15 or 27, same amperage as the failing one but just more robust looking.   Pulled it apart, tested diodes then put it back together and tried to install it.  Very close to fitting but the rear bearing ran into the rear bracket so no go. 

Took apart the failing one and found one of the 6 in the bridge open and one in the trio open.   Noticed that the other parts were very similar so decided to see if I could do some swapping and make a working one.  I think I had to do a little too much grinding or maybe forced the bridge in before grinding enough or maybe didn't get the insulated regulator screw back in the right hole because I had zero output.

Thought about trying to figure out why and make it work but then decided I had enough fun and learning so I ordered a replacement and it will be at my local store in the morning.   

[cadillacmike68]

Is there an auto electric shop nearby? If so, then can rebuild your original for you, and even increase it amp output (up to about 80 for a 10SI or 140 for a 12SI).

[chrisntam]

There's prolly a you tube video on how one comes apart and goes back together...

Don't you just put in a paper clip to hold the brushes in place while the case is cracked open?

[Mike Josephic CLC #3877]

If it were my alternator, I would have it rebuilt.  Hopefully,
there are still a few reputable repair shops in your area. 
We have a couple in my area (Pittsburgh) so you may be
lucky.

Many of the replacements sold today are a crapshoot at best. 
Quality of many of these are spotty since components used
in the rebuilds are garbage (Chinese).

Mike

[Cadman-iac]

There's prolly a you tube video on how one comes apart and goes back together...

Don't you just put in a paper clip to hold the brushes in place while the case is cracked open?

Unfortunately you can't get a clip or whatever you use to get between the brushes and the rings. The hole is not in the right place,  as it's supposed to be for reassembly and keeps the brushes back away from the rings so as not to cause any damage during the assembly process. Good idea, just won't work.

Rick

[bcroe]

. \Is there an auto electric shop nearby? If so, then can rebuild your original for you, and even increase it amp output (up to about 80 for a 10SI or 140 for a 12SI). 

Decades ago I installed a kit for increasing an alternator output.  I
do not know just how they did it, but it seemed to me to run very
hot all the time.  I did not really need the extra output, so I decided
it was not a good idea. 

Later diesel cars were hitting the junk yard, and I managed to find
enough of those somewhat larger alternators to equip every car,
plus as many spares on the shelf.  They got the bearing and brush
update, and still serve me today.  I put each one on a car for a few
thousand miles before moving to the spare pool, just to be sure
they were trustworthy.  Yea they are numbered per cards in a file. 

Huge alternators encourage belt squeal.  Bruce Roe

[TJ Hopland]

I used a piece of MIG wire to hold the brushes back because that was easier to find in my garage than a paper clip.   I don't see any way you could pre install it so you just have to lift the rotor and front out and let the brushes pop out.  They are hooked to wires so they can't go far. 

Getting them back in is quite a project and much easier if you remove the outside winding things.   That's pretty easy just 3 nuts you have to remove and it lifts out of the housing.   That gives a little more room where I get the rear one in first then retain it with the wire while working on the front one.  I didn't have any issues with either of the ones I was playing with with the holes aligning. 

After getting into my 'original' I was not worried about saving it.   There was nothing very special about it quality wise.  Who ever had assembled or rebuilt it wasn't careful and kinda mangled the stator lugs and chewed up the nuts.  The slip ring commutator thing wasn't true you could see by the very uneven wear from the brushes. 

Got the rebuilt one installed yesterday.   Boy did that long lower bolt fight me going back in.  No idea why it put up such a fight.  Must have struggled with it for 30 mins.  For being on top it did suck to access.   One of the trans cooler lines is just about in front of that bolt so you can't easily get tools or your fingers on the bolt. 

New one seems to be charging fine.   Does have a different sound especially at first but it my have quieted down after a 30 min drive last night.  Its not crazy loud but since I was listening for it I could tell something was different.  That is on top of my super duty fan clutch, likely soon to fail power steering pump, electric fuel pump, and open air cleaner.