meh

'85 442 with '79 Toro 403
Battery seemed weak lately
I thought I saw the volts gage down around 9-10 the other day
Snugged up the thin belt that runs the voltmaker.

Last night, while exercising the car, under full throttle, the wife noticed a red light on the dash. Not oil pressure... alternator light.

Sure enough, under heavy throttle, the alternator or whatever they word it on the '85 light comes on.

Then it goes out right away to pretty soon.
Only comes on dimly under moderate acceleration.

Pull the 'nator and have it ck'd at the store?

Any other suggestions?

 

I agree - I can't see this as being a belt-slipping issue, as even if they slipped at high RPS, they shouldn't slip enough to give you zero charging.

HOWEVER, since it's ONLY a high-RPM issue, the store test may not reproduce the conditions where you had the problem.

I'd run another voltmeter (the factory ones are inaccurate and slow to respond) and watch to see what it's doing, to see if you get any more clues.

- Eric

 

Check for a loose connection also.

 

Yeah. Assuming it isn't a loose belt, I had exactly this problem with a 12SI in my 86 with a 307. The GEN light would come on under moderate to hard acceleration only. I rebuilt the alternator, only to have the same thing happen. I took the alternator apart again and inspected it closely. Turns out that the commutator slip rings were out of round. At high RPMs they were acting like little cam lobes, causing the brushes to bounce off the slip rings. I chucked the armature in a drill press and trued the slip rings and that solved the problem.

 

Wow. Never heard of that problem.

Let us know how it turns out.

- Eric

 

It could be the problem. Could also be a burnt stator connection. Common on the 12SI. I always turn the sliprings in a lathe to be true. I think it is critical especially on newer alternators with smaller diameter sliprings. A bit of brush hop on a large diameter slipring may mean the brush skips 1/8 of the circumference while the same hop on a smaller circumference ring may miss 1/2 the ring. Also there is almost always a groove worn from the old brushes and new brushes will not seat properly unless there is a fresh new surface to wear into. Take a good look at the stator crimp connections where they connect to the diode studs. They tend to get hot and burn there. The crimp is made over varnished uncleaned wire from the factory. If burnt, a good cleaning with a wire wheel and or knife and then solder will correct it.

 

I chucked the armature in a drill press and trued the slip rings
===============
Interesting...

 

Well, it was the closest approximation to a lathe that I had at the time. Mount the commutator end towards the chuck and don't press hard on the slip rings and you get a passable job.

 

Any port in a storm...

- Eric

 

WOW, how many people in readerland would have thought of that? Never seen that, probably never will!

 

Bought a new battery ($140) because the old one was toast.

Still does the slight "CHARGING SYSTEM" light under higher RPM.

Removed alternator and took to store- checked OK

Looked like the belt, of dubious origin anyhow, was riding way down in the grooves. Thin belt, maybe 7/16". Adjustment was all the way out and still not really tight.

Got new belt today- old belt was about 3mm wide at the narrow part of the Vee, new belt about 2x as wide at that area. That's as far as the process got at this time, have not had a chance to road test it and see how it does now.

 

Drove it today
same story
new belt did not cure it
RPM's above 2500 or so I get a dimly lit CHARGING lite.
Voltmeter is a little under 13 on the highway

Next clever idea is to swap out the alternator I guess. Open this one and take a peek.

 

Let us know what you find in there.

 

I'll bet that you have diodes gone in the alternator ,my light just started to glow slightly the last start up so I read a little bit up on the problem and it's pretty common especially if you've had any kind of a short ,which I did ,I was fooling around with the horn relay,trying to clean it up and I inadvertently caused some sparks and next thing i know the alternator light starts to glow.Sum Dum Guy eh ?