Alternator rebuild

[Todd L.]

I have an aftermarket alternator on my 74 LS4, I found out it is bad. I do not have the funds right now for a correct date coded unit, and I do not want to spend money on another aftermarket if I do not have to. So I have the bad one taken apart.
My question is, using a multimeter can I take readings of the individual components and tell if they are good or bad? What should the readings be? Enclosed are some of the components. There is also a coil with three wires off of it. What should my readings be across them?
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[Edward M.]

Re: Alternator rebuild

Parts store sells replacement alternators for $20 to $25. Not worth messing with the internals unless you are restoring an original.

Sorry, I can't be any more help.

[Patrick H.]

Re: Alternator rebuild

I agree.

I replaced parts on a date coded alternator a few years ago. The parts cost almost as much as a Pirkle rebuild by the time I was done.

You're far better off from a money perspective just buying a rebuilt unit from the parts store.

Double check the numbers on your current unit first to be sure you shouldn't sell it on ebay and make money on it.

[Terry M.]

Re: Alternator rebuild

The above posters both give you good advice. Get another generic alternator and be happy driving your car.

We used to teach alternator and starter rebuilding in auto shop, but we no longer do that. Mechanics no longer rebuild these units in the field and this has made parts for them hard to find. Your FLAPS used to sell rebuild kits for these generic GM alternators (SI or System Internal units). They may still be able to get these kits, which may include the bearings, but I doubt they stock them. Check availability and prices before you proceed.

I don't have the time at the moment to give you a step-by-step, but the Overhaul portion of your 1974 Chevrolet Factory Service Manual has a step-by-step how to trouble shoot and replace any defective parts.

The part in the first two pictures is the regulator.

The third picture is the diode trio.

The last picture is the brush assembly.

Check the manual, but I don't think the multi-meter will help for the regulator, but I might be wrong. The multi-meter will be most useful for the diode trio, but you will need the step-by-step and the illustrations for that. The brushes are strictly a visual inspection. Look for a wire disconnected and the length of the carbon brushes. Those look short and I would replace them.

The coils you refer to are the stator windings and those can be checked with a multi-meter. Again the step-by-step with illustrations is in your manual.
Your FLAPS used to sell an internally regulated rebuild kit.

[Ridge K.]

Re: Alternator rebuild

Whenever one of my neighbors asks about non-numbers matching parts, and they don't easily find them at the local autp parts store, I recommend www.autoparts123.com.

They offer free UPS shipping (48 hours).
I just checked and they have your 1974 454 alternator for $29.36
or,....
They also stock the parts to rebuild, for cheap $$

Hope this helps. Ridge

[Jim T.]

Re: Alternator rebuild

I have repaired the alternators on my 68, 70, and 85. Most of the repairs consisted of replacing the internal voltage regulators on the 70 (160K miles)and the 85 (102 miles).
Last time I replaced the voltage regulator in my 85 I bought the replacement voltage regulator, not a Delco part, from Auto Zone. Don't remember the specifics of the situation now, but I ended up going to my Delco parts store and they ordered me a specific Delco (GM #1116423 ACD# D680 Made in USA) voltage regulator for my 85 Corvette that I installed.
There is a test with your alternator on the car to check out the voltage regulator with your car running.
Your picture of the voltage regulator shows exactly what you need to touch with a screwdriver coming in from the back of the alternator. The touch point is the little tang at the bottom of the voltage regulator you have posted. By touching this tang and grounding it, if the alternator charges, your voltage regulator is why you alternator is not charging.
Corvette service manuals have the information to check out the internal parts of an alternator.
Most of the not charging problems with my 70 were internal voltage regulator replacement, probably about 3 times in 38+ years. Always used Delco internal voltage regulators.
Only one internal voltage regulator failure on my 85, used a non Delco replacement that was replaced with Delco part.

[Todd L.]

Re: Alternator rebuild

Thanks all. What happens when I find a correct alternator and I need a rebuild? I do enjoy doing the work and learning in the process. How do you make the case look new or original? Looks like I need to purchase a repair manual.
Todd

[Harry S.]

Re: Alternator rebuild

Just got my Alternator back from John Pirkle and it looks great. Too much snow on the ground now to jockey cars to install it. I'll wait till May after all the snow melts.

I asked him about how he restored the outside finish. He said, alot of work. That's one of his secrets I guess, that's ok with me.

[Jack H.]

Re: Alternator rebuild

Your copy of the Chassis Service Manual provides basic electrical trouble shooting steps that can be accomplished with VOM. The Chassis Overhaul Manual gives a section on rebuilding the alternator from the same perspective. It's beyond me to recite the details that are already documented. I'd get the book(s) if your objective is to learn the diagnostic and repair proceedures.

But, remember these step by step proceedures were written for BASIC repair and the go/no-go tests outlined for execution by shop mechanics with limited diagnostic tools (continuity probe, VOM, Etc.) while necessary, may not be sufficient to find 'exotic' failures.

By this I mean things like diodes that have suffered junction puncture and have a Jeckyl/Hyde performance profile (works A-OK when cold, but fails when it's hot or passing max current). The steps catch 'most' of the problem issues but not all of them.

[Todd L.]

Re: Alternator rebuild

Well, I guess I missed the boat. I was searching for the chassis service manual for a 74 and found it was out of print along with the 73. Like they say do not procrastinate.

[Christopher K.]

Re: Alternator rebuild

Todd,

Look on ebay for the chasis service manual (look under '74 corvette or corvette parts). Don't pay too much, you can get them pretty cheap with a little searching. You may even find it on CD.

Chris

[Jim T.]

Re: Alternator rebuild

Todd L. the Corvette shop manual is available from the original publisher for 1974. This is not a Corvette specific shop manual other Chevrolet cars are included, they have not been this way for years.
Contact www.helminc.com to order, before there was a NCRS I bought my manuals directly from Helm. Owners manuals provided a order blank back when we ordered by mail and not from a web page. 800 number has been used as well.

Helm #ST32974 is for the 74 manual

Helm #ST32973 is for the 74 manual

You have not missed the boat yet.

[Todd L.]

Re: Alternator rebuild

Is the capacitor in the alternator just for reducing the noise on a radio equiped car? If it is or is not is there an advers affect to removing it?

Todd

[Harmon C.]

Re: Alternator rebuild

Todd
If you are a hands on guy pick up a few alternators at a local car show.
I have bought some for $1. with the same case. Pick out a nice one and test it. Many times they work fine. I built a tester with an electric motor drive to test my work. E-mail me and I will tell you how to restore an original case if you find them with the correct numbers.

[Todd L.]

Re: Alternator rebuild

Ok,

I bought a new voltage regulator, I went to the parts store with my multimeter and compared values on my components, to the new ones. (pretty nice of them letting me do this) I found my voltage regulator was bad. I made a rookie mistake when taking the unit apart, it looked like a simple process, what I failed to notice was on voltage regulator/brush assembly it is held in place by three screws, two of which have a plastic insulator.
I do not remember which one does not receive the insulated screw. I ordered the chassis service manual from Corvette America, for $45.00 including shipping. (Ecklers wanted $100.00 for the same book, not including shipping.) It will not be here until the end of the month. I am impatient. So, if anyone can tell me where the two insulated screws go, I would greatly appreciate it.

Todd