How to identify bad alternator

[Reverend]

Hiya

I've been working with my Z for a year now and finally i got to drive it a little. Now i want to ask you oh wizard of oZ, that how (or is there any way) to recognise bad alternators? Mine is okay now but i dont want it to break down in the middle of traffic lights or in highway.

I have experienced the agony when alternator breaks, i was driving home with our daily driver Volvo 945 and i was wondering why the dash lights were so weak and i could barely see lights front of the car. After few kilometers car stalled and we needed a towtruck.

I COULD order a brand new(NOS) alternator but i dont do that if not necessary. Current alt. seems to be original..

[ozconnection]

I had absolutely no warning when my failed. :disappoin

Replace it now if it worries you.

It's only money and your baby

[Gary in NJ]

If paranoia was a legitimate reason to replace things, I wouldn't have enough money to pay the mortgage on my house. If it's not broke, don't fix it.

The gauge that sits above your radio, the ammeter, is your window to a properly working electrical system. As long as the needle continues to swing to the (+), your alternator is making power and the regulator is regulating how the power is delivered back to the battery.

[Davey G]

Interesting timing on this one. Mine failed Thursday evening on I-10 50 miles west of Houston. I sat on the side of the road until midmight as my friend I was following did not notice me pull over, and could not hear his phone ring any of the 15 times I tried to call. :mad: I got it back to the Walmart in Sealy after a jump and parked it.

However, the next day when I checked, it had a battery with a failed cell and a failed alternator. I found a battery, then on a whim checked with the local O'Reilley for the alternator. Lo and behold they could have a rebuilt one there by 4:15 PM the same day! I told them to get it there, but honestly thought it would be the wrong one. But when it arrived it was the same as my Hitachi...it was a Hitachi...and for $60! I installed it in the Walmart parking lot and was on my way. Kudos to O'Reilley for having Z parts in stock.

I kept the bad alternator rather than turning in the core as I intend to have it rebuilt in Houston and ready to go should this one fail over the next few years.

[Reverend]

Allright, maybe im a little paranoid Guess you cant never know what's gonna happen next. I better find a good alternator just in case current one fails. Actually i just remembered that alternator failed also in my other Datsun (150Y) few years ago.

BTW: What kind of alternators will fit 240Z? Do you need to do lot of changing if installing a bigger alternator..?

[FastWoman]

Check your system voltage after starting your car. It should be somewhere in the range of 14-14.5 V, as I recall. If it's putting out that voltage, then it's charging your battery and holding up to the electrical load that's on it. Then turn on everything electrical, and rev your engine while repeating your measurement. I would think the system voltage should be AT LEAST 12.5V to maintain your charge while rolling down the street at night with the radio going. The 40A alternators are a bit on the weak side. Other Z owners with 40A alternators might be able to give you a better idea what operating parameters are normal.

You just have to keep an eye/ear out for anything that's sounding or operating "differently" and only THEN get paranoid that something might be going wrong. Usually "different" behavior means something has gone wrong, as it would only rarely mean that something has spontaneously gotten better. You should always keep a loose eye on your gauges anyway.

You won't get stuck on the side of the road if you catch your alternator problem in good time. You'll be driving down the road, realizing that your headlights are getting dim, and/or your radio is sounding rather scratchy. Then the light should go on that something might be wrong. You check all your gauges, and the alternator gauge is hovering in (-) territory. You then turn off everything electrical, and head towards the closest auto parts store or garage. You're likely to make it, as long as the engine doesn't stall out, especially with a carbureted engine. Your ignition can probably run off of as little as 10VDC. Of course you'll need a jump start wherever you stop your car.

You can install the 60A alternator of the later Z models, but your main alternator wire might not be beefy enough to carry 60A. I know the main wire in my '78 (which was designed for a 60A alternator) was not really beefy enough to carry 60A with its stock wiring. I installed a much heavier wire to correct this problem. You'll also need to install a diode on the field coil, as I recall, to keep the power from back-feeding and keeping your engine running even after you turn off the ignition key.

[sblake01]

I never had a problem with the main wire on my 78 in the 12 years I owned it and I'm sure it was original so it held up fine for at least 31 years that I know of.......

[Davey G]

I never had a problem with the main wire on my 78...

But doesn't a larger gauge wire here let the headlights burn brighter...or was that on the older cars only?

[Bruce Palmer]

Ya know, this conversation baffles me. If one is morally and/or ethically opposed to standing along the side of the road with his 40 year old fill in the blanks car, why it wouldn't make sense to find a local electrical rebuilder and buy a unit or have yours gone through. Maybe we are spoiled here in Salem OR but we have an excellent rebuilder who builds top quality stuff and for $40 we can come up with starters and I think for not much more than that a 60 amp alternator..... Water pumps are the same thing. Put one in and you know the history. Don't put one in and be surprised when all of a sudden it tells you it's history. Belts, hoses, hydraulic cylinders and fluids all the same deal.......

As further editorial comment I'll say I would not go to fill in the blanks parts chain and buy one of theirs 'cause those get "built" in some minimum wage sweat shop and any warranty failures are just a cost of doing business. Minimum product out the door for the maximum dollar..... and with an extra markup in the for the extra step in distribution.....

Carry on.....

[sblake01]

But doesn't a larger gauge wire here let the headlights burn brighter...or was that on the older cars only?

That may be true but I'm talking about a 78 as was she in that case. I'm just saying basically, 'if it ain't broke, don't fix it' based on my experience with my 78. Edited August 24, 2010 by sblake01

[FastWoman]

Steve, the insulation on my main alternator wire was a bit toasty! I don't know whether there was some mishap prior to my ownership, but the alternator was apparently able to put out enough juice that the fusible link did not adequately protect the main wire. As far as I could tell, the fusible link on my car (in stock configuration) was good to about 80A, with the alternator good for 60A. That's all fine, except the 10 ga alternator wire was probably good to 40 or 50 when wrapped inside a harness w/o airflow, even assuming current didn't have to pass through a couple of crusty crimp connections. Trust me that it was definitely "broke!" The problem was in the design. Datsun made a great car overall, but their electrical wiring left much to be desired.

Davey, I ended up with brighter headlights, but I don't know how much of that to attribute to the alternator wire. At the same time I did that work, I upgraded my fusible links to maxifuses and installed headlight relays. After I worked through all those trouble spots, my headlights were indeed much brighter, and my electrical system seemed much happier overall. It was like giving an inhalor to someone with asthma.