My battery has been dying on me
My voltmeter reads only 11.8V at the battery with the engine at idle.
In this situation, would you guys simply replace the alternator?
I would greatly appreciate any advice. Thanks!

RON
Houston,TX

 

Need to get it checked at least. Up off idle what does it read?
Have you charged the battery with a charger? How long does it last?
Checked for batter drains? Ctsy circuit, light timer?

 

Charging systems should be checked with the battery charged and tested first. A quick check is that the voltage read at the batt with eng running should be a min .5 V above batt voltage with engine not running. With a fully charged battery, or as the battery charges the voltage should climb to about 14.2. It should maintain that at normal idle speed with no accessories running. With all accesories on the charging system should maintain the .5 V above standing voltage at fast idle, but may drop below standing voltage at curb idle.

If you were of a mind to fix this yourself there is a next step if it's not charging. There is a small hole in the back of the alt case near where the small wires plug in. This leads to a metal tab on the back of the internal voltage reg. Using a small screwdriver, with the engine running, insert the screwdriver and ground the tab against the side of the hole. This bypasses the regulater and provides full feed to the field. If it starts charging your problem is the regulater. Simple matter from there to split the alternater and replace the reg. Clean the slip rings, replace the brushes if nec. Lube the rear bearing cup and check the frt brg. Total cost probably around $15.

Repairing the alt itself isn't much harder, but a longer post.

Steve g

 

I would take the alt to autozone and have it checked but I think you have a dry cell in the battery and that causes the alt to only send out what the battery can handle.

 

If I were to bet on it....I would swap the alt and be done with it....

 

That's the way the dealer shops deal with component failures nowadays. If it is under warranty, no big deal, but if the customer is paying, replacing an alternator or wiper motor, or whatever is BIG BUCKS.

Back in the day, a component or part was often repaired. The Chassis Overhaul Manual gives step-by-step instructions on testing the voltage regulator as Steve2147 did a few posts above this one. Fix the easy things and save your $$ for the big stuff you can't or don't want to do yourself.

 

Thanks for all your replies!
Okay, so I decided to just go ahead and replace the alternator. I went online and see amp ratings ranging from 37 to 80. How important exactly is this?

 

I buy the lifetime alt's so it's just my labor to swap out, and in my world with what he described it's always the alt....and no way do I have time to rebuild what is now in most all cases an exchange part,
Some alts even need special tools to rebuild them right...

Pretty important especially if you run high draw stuff, like electric fans high end stereos etc.....I run a 105 amp unit and it runs my stuff but I would go higher if I had a kicking stereo....if you are bone stock 80 is okay...but cant hurt to have a bit extra....

 

Quite. Means the difference between whether you're taking out more than you're putting in or not. Putting 37 amps into a system that's consuming 50 or 60 means your battery is going to still be going dead on you.


Check the stampings on your old one and replace it with the same amperage.


Steve g

 

Just get the larger amp output. It will only put out what it needs.

 

In case the new alt. still does not put out enough volts check the pulleys. Guy before me put a underdrive pulley on the crank and that was it, put a larger pulley on and fixed everything all my issues. Took awhile to figure it out.

 

85 amp

http://www.autozone.com/autozone/par...40_23521_4430_
http://shop.advanceautoparts.com/web...RPALTSAMS_____
http://www.oreillyauto.com/site/c/de...1468&ppt=C0330

 

I'd have it tested along with the battery after fully charging it. Most all alternators that I have seen either worked or didn't. 9 times out of 10 it is the battery.

Tel us what it ended up being. My money is on the battery. Be sure to have the old alternator tested before buying a new one. going to have to take it in for the core anyway.

Also are you sure your cables are making good connections and there's no corrosion?

 

Partial operation of an alternater is very common. The rectifier has 3 sets of diodes, one neg, one pos in each set. What frequently happens is one diode quites so you are working on 2/3's output.

When they quite entirely it's frequently not the alternater itself at all, but rather the internal reg. If it's the alternater itself that quit altogether all at once, brushes are the suspect. Seldom do all 3 sets of diodes in the rectifier quit at the same time.

Steve g