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continuing saga was:bad diode stator means?

Update on bad diode stator (alt) post below:

more on my continuing saga of a simple repair that gets complicated below:

jim wrote in news:1186323461 snipped-for-privacy@sp12lax.superfeed.net:

> sorry wrote: >> >> Sorry to keep bugging everyone about this, but I just don't know. >> 77 dodge van 318. On startup ammeter needle swings from full >> charge to midrange. Loud squealing when ammeter needle swings to full >> charge. Noise goes away after engine warms up. I think I tried >> tightening the belt long time ago and made no difference. Visual >> inspection of belt appears ok. It is one of those kind that is >> serrated on the pulley side, but no glazing or obvious wear. >> >> Looking at a shop diagnostic report sheet from long ago it is >> somewhat illegible but says, under "Alternator Output: Bad Dode >> stator" which I guess legibly written means: Bad Diode Stator? Would >> this cause the noise? The belt looks ok and I brought the alternator >> down to Autozone for them to test on their machine. Test said it was >> ok, but Mgr. there said it was probably a bad diode in the >> alternator. > > So what to do. Do you believe the test or do you believe the manager. > It would seem to me that if they have a machine to test alternators it > would be able to detect a bad diode.

I bought the new alternator from AZ, but it had an metal sleeve insert one of the bolt holes and would not install properly, due to insufficient clearance for a spacer at the back of the alternator, and this metal sleeve. I did install it, but the pulleys did not line up properly and, of course it steal squealed.

>> Should I buy a new alternator and see if the noise disappears? > > What is the noise? Your description leads one to believe the noise is > the belt slipping. If that is where the noise is coming from it is > unlikely to be a bad diode. By now one would guess that you have > probably overtightened the belt so the belt being too loose can be > ruled out.

I agree, the test should have picked up the bad diode as they seem to have a very sophisticated machine at autozone specifically for testing alternators, but the manager there persuaded me it could still be bad. Also the noise went away as the vehicle warmed up, so that means it's probably not the alternator. Thing that confused me was earlier report of bad diode stator, which I am only guessing came from a scope reading. It is also possible it could be BOTH the alternator and the belt.

I think it is the belt, one of those serrated on the pulley side belts. I tightened as best I could. I could not find a pry bar that would fit into the small slot between the bolt and alternator body and was risking breaking my wrist with the one that I used. I got the belt to tension close to the manual recommendation of

1/2 inch deflection. I also lightly sanded the pulley grooves, the areas I could reach that is.

I also bought some belt spray, don't know it that will help or not? I have not tested it yet with the old alternator back in and pulleys now aligned, but I think it probably will still squeal. I cannot replace the alternator belt, since by doing this I also have to remove the PS belt and the unit is frozen with a rounded off bolt and my location is such that i cannot do extended repairs. I am planning on selling the vehicle, so just going to either sell it or store it. A simple repair is turning into a royal pain in the arse.

If your gauge truly measures amps then it is normal for the amp > rate to > go high after starting. It may be that it always did exactly what it > is doing now - only you never noticed because there was no loud squeal > to draw your attention to it. Or it could be that it is now charging > more than it used to because of a bad starter or bad engine or some > other unknown draw on the battery that requires a lot of amps to > restore the battery. A weak diode could be draining the battery. > Another possible cause of the problem is a bad belt or the wrong > belt > for the application. I assume this is a v-belt so the cause could be a > worn pulley given that the vehicle is 30 years old. If the pulleys and > belt don't fit together as designed you can get the symptoms you > describe. > > -jim >
Reply to
sorry
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Just after operating the start motor, the battery state-of-charge is down, so more power is required from the alternator to charge it. More torque applied by the belt to turn the shaft, belt slips, and makes noise.

Battery state-of-charge comes up, less power required from the alternator, not as much power through the belt, so it quiets down.

Bad diode or not, (probably not) the alternator IS working. And a bad diode will not cause the squealing sound you have described. What will cause it is a slick, worn out v-belt trying to put about 3 bhp into driving the charging system at full grunt. This is a CLASSIC case of a worn v-belt slipping.

Reply to
the fly

Since there is no such thing as a "diode stator," odds are good that someone was pulling your leg.

Connect a volt meter to the alternator output stud and ground, set the volts to read AC, any AC voltage above 100 millivolts would confirm a bad diode. Shitcan the cogged belt, they aren't used OEM and for good reason. Shitcan the belt spray, that stuff just makes a gooey mess to clean up and will probably make the squeal worse.

Reply to
aarcuda69062

There are some meters that will take pure DC, and read double the voltage on an AC scale. That is, hooking one of those to 12V pure DC will give a reading on the meter's AC scale of 24V AC. So if the reading from the alternator is anything above 15V, use a different meter.

Reply to
clifto

You got that right! Some meters do not read ripple correctly when DC is present.

Re Aarcuda, we always called the section holding the diodes a "diode plate", but not a diode stator. Dont know if that is still the same.

Reply to
hls

Okay, so first of all you ignored our advice to first replace the belt, and THEN you went and bought a crappy chain-store alternator that didn't fit properly.

It's possible. Personally, I'd trust your original alternator more than the AZ replacement, though.

Considering that the belt is cheap and the alternator is expensive, it would seem that replacing the belt would have been the FIRST thing to do. And replace the belt with the dealer part, not some cheap chain store junk.

Probably not, no.

I hate to point this out, but you are making it so. Cut the bolt off, take the steering belt off, replace the alternator belt, put the original alternator back on, and go. While you are replacing it you might want to replace the power steering belt too. It's something that you just need to do every few years. Belts are wear items.

--scott

Reply to
Scott Dorsey

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