72buickgs

The alternator on my T/A failed Thursday last. It started howling on startup & when driving, voltage would rise & fall & then stopped at 12 volts..
Since car is all original, I would prefer to rebuild. If I have to wait beyond this Friday noon for the work, at the local rebuilder, I may purchase a rebuilt unit & rebuild the old unit later.
I am guessing that it it is a 12Si just by the year.
The Service Manual for this car with V8 (not HO) states that generator/alternator usage is Std=42, HBL(?)=78, heavy duty=78
There is no stamping/marking to indicate the amperage output. There is a stamping on the back side of "7G"
Ideas?
see attached

8t2 z-chev

That is a 12si.I if you have AC,probably 78amp-"HBL"may mean defrost grid on hatch glass.Stamped into the case,just behind the upper mounting lug,should be part # amp rating and date code Probably just brushes worn down,auto parts stores used to sell repair kits for these alternators.

sofakingdom

iTrader: (1)

The ACTUAL OUTPUT capability, as well as the "ratings", of alternators, depend on parts other than the castings. That is, you can collect armatures (the rotating piece), stators (the stationary coil assy), regulators, rectifiers, etc., and FREELY mix & match them, and jam them into ANY castings you want with ANY "ratings" whatsoever stamped into them. Even those with the "rating" stamped on the front casting may not be whatever that says AT ALL, especially after they've been "rebuilt". Which unless you've owned the car since it was new, you have no way of knowing, butt in general, if it was more than 10 yrs or 100k miles old when you got it, it probably isn't the "original".

A trip to a "rebuilder" will show you how/why. They tear them down: all the pulleys go in a barrel, the front casting (with "ratings" stamped on them) in a *******, the rear casting in another *******, the armatures in one basket, the stators in another, and so on. Each goes through its procedures of cleaning, blasting, painting, etc. etc. etc. as appropriate. Then the "assembler" grabs one front casting and one armature and one new bearing (6203ZZ FYI, 17 x 40 x 12mm, 2 rubber seals) and one retainer plate and 3 screws and assembles a front; another grabs a case rear, a regulator (new? who knows unless you're watching or if they tell you afterwards? do you believe them?), brush holder (new?), new brushes, diode trio (new?), rectifier (new?), rear bearing (new?) resistor (sometimes), stud insulator, and a handful of nuts and screws and insulating washers, and assembles a case rear; then the 2 halves are joined. Any relationship that any of those parts ever had to any others, including the "rating", is LOST. Some rebuilders are more careful about that than others; they might for example segregate rotors by their resistance and/or # of turns, the stators by wire diameter, and so on, butt again, if you're not watching, you have NO IDEA whether they did that or not. If you have a bunch of em laying around you can inspect the parts that determine the "rating" and make yourself whatever you want: look for the armature that has the most turns of the largest wire you can find, the stator with the largest wire, and always use a resistor. See this thread here for an example.

https://www.thirdgen.org/forums/elec...nals-drop.html

Alternators are EXTREMELY eeeeeezzzzzy to "rebuild". Especially if all that's wrong is, a howling bearing. If the alt you have now has provided satisfactory output while you've had it, there's no reason not to do that. And if it's still good electrically, you can do that for so cheeeeeeep it's almost embarrassing.



Of course you can always try to source these things locally, butt most people will look at you like you have 3 heads if you ask for a bearing by its generic number, rather than year make model and part name. If you have an actual bearing store where you are though, they'll know exactly what you're talking about. (yes I used to work for a place that sold, among other things, electric motor rebuilding supplies including bearings, so I'm pretty familiar with bearings in a general way)

Pop the pulley nut off with an impact. Mark and split the alt case; unscrew the 3 screws that hold the bearing retainer in the case front (kind of a PITA to get to but manageable); pop the armature out, sand the slip rings lightly with about 180 grit sandpaper, and clean every trace of grit off of the armature; pull the old 6203 bearing off; install a new bearing in the case front and put the retainer plate back on; grease the armature shaft very lightly and press it back into the bearing; install the pulley.

Unscrew the 3 nuts holding the stator wires to the rectifier and remove the stator; remove the screws holding the diode trio, regulator, resistor, and brush holder in place (take pics on your phone as you go to make sure you get the parts and screws and insulators and whatnot back in all in the right order); replace the brushes; clean out the rear bearing with spray carb cleaner and re-lube with white lithium grease, being careful not to get so much in there that it'll sling out and get on everything inside the alt; push the brushes in with your finger and stick the toothpick or small straight piece of soft wire or whatever in the holder, to hold the brushes back.

Reassemble the diode trio, regulator, resistor, brush holder, and stator. Put a dab of grease on the case screws and put the case halves back together making sure to "clock" them the same as they were so the output stud is in the right orientation. Tighten the case screws to around 5 ft-lbs (60 in-lbs). The toothpick will stick out through a little hole in the back of the case; pull it out. Reinstall.

Too eeeeeeeeeeeeezzzzzzy.

8t2 z-chev

OP's Alternator looks clean enough to be original:casting flash is still nice and sharp,case bolts all match,and has correct fan and pulley-not ford items like is often seen on rebuilts and you are right-super easy to rebuild.

72buickgs

THis is the original alternator. Car is original unrestored, except maintenance items. has about 26000 miles.
If I cannot get it rebuilt by this coming Friday, I may buy a rebuilt unit & have the orig rebuilt later.

72buickgs

Sofakingdom
Your instructions are easy to follow. I am quite capable of performing the repair. I may just purchase a quality rebuild kit (not Chinese) & give it a go.
I actually watched a rebuild on Youtube.
Just checked & located the stamping. It is a 78 amp alternator.
Tkx

72buickgs

I had the alternator rebuilt by a local firm last Wednesday. Cost me $113 including tax.
Saturday, I proceeded to drive to huge car show in Bothwell Ontario. I left home at 4:00 a.m. Of course I was using high beams & low beam lights as I drove.
60 miles later, I reached Chatham On. At the red light, I was about to turn right when I noticed the voltmeter suddenly drop to 13 volts.
I was concerned then that the battery would fail. I have CAA premium coverage if I required a tilt 'n load recovery.
I drove on & the voltmeter stayed at 13 volts. The lights never dimmed. Thus, the alternator was generating enough power to keep the car running & not kill the battery.
I reached the show area in Bothwell & parked my T/A in an entry line. Twenty minutes, I started the car and low & behold the volts jumped to almost 15.
It worked fine for the day as I drove another 30 miles to Watford On to my sister's home for a show on Sunday.
Yesterday after a ride home from Watford of 2.5 hours of driving, out of curiosity, I took my infrared temp detector gun to check the temp of the alternator and it read 150*F !
Damn hot!
Would probably be hotter if I was using the headlights.
I think the alternator failed due to excessive heat !
Back to the rebuilder for another "Chinese Kit" this morning.
Will let u know the result of this rebuild.

8t2 z-chev

rebuilder should know,but common problem with "old skool"GM alternators is bad connection between the stator lead wires and crimped -on ring terminals that connect to the rectifier-soldering the connection fixes this,and lets all 3 phases work.

72buickgs

I took the alternator to the shop & he placed it on a tester (old school) & ran it at 100 amps for over a hour with no failure.
It was not very hot to the touch. I reinstalled it & drove a couple miles & checked the temp - 150*.
I drove my truck, 2015 Colorado for a few miles & checked the alternator temp - 140*
I reset all the grounds as he suggested. He also stated a battery that has 12 or more volts & load tested could also be drawing too many amps to recharge it.
He experienced this situation. To satisfy a customer for whom he had rebuilt his alternator, similar problem as I had, he tried two of his own rebuilt unit & proved the battery bad as his units showed the same problem as me.. New battery solved the problem.
The battery had to be recharged last tweek because I inadvertently left the dome light on & battery volts were 9.0. Perhaps, eventhough it recharged & holds about 13 volts, it is damaged. Only a year old.
It will be a month until I have to drive for at least 2 hours in the dark with headlights & taillights on. See if problem reoccurs. Will check alternator temp at that time.

8t2 z-chev

Batt probably ok,I recently abused one of mine far worse-left radar detector on (classic escort from 1982) and did not use the car for 2 weeks-pulled batt to 0 volts:expensive AGM about 5 years old-my modern battery charger thought it was a 6-volt battery and only charged it to 6 volts,so i had to get out an old charger to get it back up-so far no noticable difference in performance-did compression check with a lot of cranking and batt kept up

72buickgs

I may have solved my problem.
I added a ground strap from engine to chassis to see if that would make a difference (I had to do in my 1972 Buick GS way back as it was missing)
Here are the volt readings at various times in my 20 mile run.
1) engine off = 12.66 lights off
2) at idle = 14.6 lights off
3) after a few miles = 14.6 lights off
4) lights on = 14.36 & alt temp = 160 tops
5) after 20 miles on the road at various speeds back at home = 14.36 alt temp 160 tops
My next out of town long run is in a couple weeks, so I will cross my fingers & hope problem is solved!