'67 small block alternator

[Keith N.]

I took my '67 for a drive last night and every time I pressed on the brake pedal my instrument lights dimmed. When i put the car away, the headlights retracted very slowly. I turned off the radio and they moved a little faster but still slower than usual. I got a new battery in April. Does this sound like it might be the alternator?

[Bill I.]

Re: '67 small block alternator

Keith, could very well be. Do you know how to test at the battery with a digital VOM? If not reply & we'll walk you through it, easy. Bill.

[Keith N.]

Re: '67 small block alternator

Hi Bill; Thanks for replying. I'm sorry I don't know how to test with a VOM. Any advice would be sincerely appreciated. Regards; Keith

[Bill I.]

Re: '67 small block alternator

Glad to help Keith. We need 3 readings. First of course, make sure batt terminals are clean and tight. If the battery is the type where you can check water levels, do so and add if needed. Now on to the tests:

1. Measure voltage at rest. engine off. write down voltage.
2. Start engine and measure at idle, and write it down.
3. Increase engine to around 12-1500 rpm and measure voltage at terminals again and record. Give me the results. Bill.

[Douglas L.]

Re: '67 small block alternator

Keith,

You didn't say whether the alternator was original to the car and motor or not, but check the drive pulley on the alternator to make sure you have the correct size pulley for your motor combination.

[Keith N.]

Re: '67 small block alternator

Hi Bill; I have some errands to run today, while I'm out I'll p/u a volt meter (don't have one) and take those readings and relay them to you. I really appreciate your time on this. BTW, is the alternator a numbered part, and judged accordingly? This car rec'd a 98 point regional top flight back in '88, and nothing has been changed since. I'm assuming the alternator is original to the car. Regards; Keith

[John D.]

Re: '67 small block alternator

bill,

FWIW I got a reasonably priced digital VOM from Radio Shack more than ten years ago and it has served me well.

[Jack H.]

Re: '67 small block alternator

Yes, alternator is numbered and date coded. The same goes for the external voltage regulator. It takes both working in properly, in combination, for the charging system to function appropriately.

What Bill is looking for from the test data is for you to report one battery voltage that's 'low' with the engine off/charging system not producing (something in the below 13 VDC range).

Then, when you start the engine and the alternator spins up, the voltage regulator senses the need to re-charge the battery and instructs the alternator to turn on and provide charging current. Voltage across the battery should climb to something in excess of 13.8 VDC (perhaps as high as 15 VDC).

While alternators are not as prone as generators to having output vary with engine RPM, there IS a modest relationship. That's why he wants you to rev the engine above idle to get the alternator working higher on its 'cut through' curve.

Getting 'er up to 1500-2000 RPM should deliver the lion's share of the alternator's rated charging current. That's IF the alternator, voltage regulator and associated interconnect wiring are intact...

[Keith N.]

Re: '67 small block alternator

Thanks for all the great info, this is terrific. Stupid question; where do i connect the volt meter? At the battery terminals?

[Bill I.]

Re: '67 small block alternator

Keith, yes at the battery terminals. Set VOM for DC voltage. Also is your car a 350 hp with no AC or TI? Bill.

[Keith N.]

Re: '67 small block alternator

327-300, no air; please define TI

[Bill I.]

Re: '67 small block alternator

TI stands for Tranistor Ignition. You don't have it. You alternator # should be 1100693. rated at 37A. Bill.