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Question about a new alternator

utherjorge

utherjorge

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I'm pretty sure that I need a new alternator in my '87 K.

I've searched through and read quite a bit about the different alternator options, and it's a bit overwhelming. My questions are very simple, I think. Please forgive asking something that has been asked a million times before.

The unit is a stock unit (so far as I can tell) that came with my 1987 K5 Silverado. On my dash gauge, I never get out of the orange above 8, and I'm taking that to mean I don't get 10 amps. That obviously makes it real exciting with the headlights on and wipers working.

I'm sure I have a drain, and the few wires I've seen with wirenuts on them (yes, I know, and I didn't do them) will be going, but I don't think the alternator charges. I'd like to replace it.

Above all else, I'd like it to bolt in. I have no plans to do dual batteries or anything fancy onboard yet, though a couple of offroad lights are in my future, I'm sure. No big subwoofers or anything like that.

So, forgive my longwindedness: what will bolt right in? Is there anything with more power than the stock alt that will bolt right in?

Thank you all in advance. My K is slowly coming together.
 
dash gauge is volts NOT amps in 87

before you go tossin money all over the place check batt volts NOT running should be 12.50-12.80 range. if missing 2 volts or more then possible dead cell in battery.

next is start motor and recheck the volts on battery to see if its 13.8-14.2 range .

and as to weak headlights do the relay mod to make it a LOT brighter and its cheep.

also fix the crappy wiring first also to help eliminate any possible problems .
 
Yup, check your alternator output with a multimeter before you go swapping in a new one. And double check that your battery is actually holding a charge......
 
In the past year, I've had three new batteries. They keep dying on me, and at least I have the warranty so that I can get the battery swapped out. The last new one was replaced three weeks ago.
 
As they said check your battery as well as your current alternator and fix any electrical gremlins that are draining your system... if everything checks out and it truly is just a bad alternator there is a good, cheap, factory option that'll bolt right in.

Madelectrical.com is a good resource for learning about your electrical system. I lost my alternator on our last wheeling trip and spent an afternoon reading up on that site and learned quite a bit. I ended up going to NAPA and bought one of these off the shelf, it's 94 amps and bolts right in place.

12SI, 94 amp, at 3:00 (AC-DELCO # 321-266, Lester #7294-3)

Tell the auto parts counter person that “The alternator is for a 1984 High performance Chevy Camaro, with 5.0L (305G) engine, 94amp alternator
 
utherjorge said:
In the past year, I've had three new batteries. They keep dying on me, and at least I have the warranty so that I can get the battery swapped out. The last new one was replaced three weeks ago.
Click to expand...

I didn't see this when I was typing my previous response. You have something draining your electrical system.

Assuming you only have one lead on each post of your battery disconnect your hot wire and using a multimeter put one lead of the meter on the disconnected hot wire and the other lead on the battery post. You've essentially hooked it back up through the meter.
Put it on a low setting since the draw is likely to be small and possibly hard to detect. Have a friend start pulling fuses and/or disconnecting aftermarket electrical components. When you get a dramatic drop on the meter you know what you just disconnected is what's putting the draw on your system, could be one thing, could be multiple things.
 
Thanks for your post.

First, I feel like a total doofus. I new it was volts, not amps. Beautiful on me. Thanks for being gentle, anyway.

Friends of mine are going to go wire by wire tomorrow before I can get there, and we'll see what they find before I arrive. I've asked them to replace the crappy wire nuts first and see what we have.

Also: this is the second starter in a year and a half. The new one now clicks while it starts, almost like it's a dead battery sort of click,but there will be jiuce and it fires.

I love electrical fun.
 
It's just the battery. If it's dropping voltage like you say the starter might turn over but will commonly make a loud clicking sound.
 
sounds like you got a case of the throw parts at it. :doah:

stop and pin down the draw problem or alt problem. then go from there.
 
Avery4jc said:
12SI, 94 amp, at 3:00 (AC-DELCO # 321-266, Lester #7294-3)

Tell the auto parts counter person that “The alternator is for a 1984 High performance Chevy Camaro, with 5.0L (305G) engine, 94amp alternator
Click to expand...


his is an '87, it should already be a 105 amp standard unit..
 
That was my next question: what is standard for me? Is it the 105 amp unit? When I checked that alternator, it looked like it was telling me it could be used on 4-cyl motors and two 454-equipped pickups.
 
Should be a CS130 alternator, and you are right it was used in a whole host of vehicles. Engine size has nothing to do with alternator output, as the 140 amp stock unit is used on a V6 minivan. Stock alternators are designed to handle the vehicle's needs.

As everyone else has said, find the draws and fix the messed up wiring before doing anything else. A bad alternator can take a battery out, but I would suspect a drain is truly causing your problem. I have a drain in Krusty, I know where it is, and since I plan a major overhaul I am not dealing with it right now, but it killed 2 brand new batteries in 6 months. Nothing else caused it, my alternator was and is good, but the drain chewed the batteries up. Find and fix the drain first, everything else will be gravy after that.

Have your buddy hook up a multimeter between the positive battery cable and the battery post, then pull fuse by fuse until the reading drops to near zero (I am hoping the draw is less than 10 amps since that is the normal max a multimeter can handle). That will be the circuit with your draw, and where you should start troubleshooting. However, get rid of the wire nuts, they are not water tight and certainly not correct in a vehicle.

As a final note, stock gauges are not the best and your low reading could easily be a bad gauge rather than a bad alternator.
 
A short curcuited wire can drain the battery,but so can a bad diode in the altenator--there are 3 of them in tandem inside it ("diode trio"),and if even only one of them fails,the altenator can still put out a (reduced) charge,but when the engine is off,allow current to backfeed to ground,and eventually discharge the battery..
If you do the "drain" test by putting a test lamp between the positive cable and the battery positive terminal and it stays lit even after pulling the fuses,it could be a bad diode--unhooking the large red wire on the stud on the altenator will put the light out if its diodes are bad..be careful not to let that wire touch a ground,as its hot all the time,and will fry fusible links--which also could be your problem,the fusible links in the red wires at the starter often fry and only let a limited amount of current pass thru them,or none,which will keep the battery from being recharged even if the altenator is fine..

I'd do all the tests already suggested before even thinking about putting another altenator on it,because if there is a short somewhere,it'll likely just fry the new al;tenator in short order...the statement about the stock gauges being notoriously innacurate is fact too,measure the voltage with a voltmeter,dont rely on the stock gauge for an accurate reading!..I've had dash gauges read in the "red" zone,then go up to "normal" just by pressing in on the dash,the printed curcuit board on the cluster can corrode and give false low readings...
You need to do the tests with a GOOD freshly charged battery too--one with a bad cell or other problems will cause a lot of wasted time and money...personally,I have had better luck with salvage yard used altenators than parts store "rebuilts",especially the bargain brands--you can buy a 140 amp one at a salvage yard for 25-50 bucks most of the time,compared to up to 200 at a parts store...most yards will gaurantee them at least 30 days,chances are if its going to give any trouble it'll be right away,not months later...
 
if its spinning it should be puting out somthing.

also check for voltage at red wire going in the plug on the side of the alt. its hot key hot. to tell alt to make volts.
 
If one of the diodes was spent though, as suggested above, would it be putting out anything? Are there any circumstances where it would be completely ca ca?

It was definitely spinning.
 
Pretty rare, more likely, assuming you are testing at the battery terminal on the back of the alternator, that you didn't have a good ground. What is the battery voltage after sitting? Battery voltage with the engine running? These are going to be the numbers we need. If the voltage doesn't change from engine off to engine running, you may have a bad alternator or a bad cable feeding the alternator. Cables like those will rot from the inside out, so if it is suspect it is better to replace a $10 cable than a $100 alternator. Even if the cable isn't the cause, it is good peace of mind to know it is good.


As for bolt in 140 amp alternators, short answer is no. It takes some wiring and modification to mount a 140 amp unit. Also, and it is very important, manufacturer rating on an alternator is 80% of it's peak output. So the 105 amp unit you have is likely capable and will put out closer to 120 amps at peak.
 
I wasn't there, and I couldn't even get there yesterday, but they told me they took the alternator out and bench tested it to get the verdict it was done. It was out of the vehicle when tested.
 
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