Alternator Adjustment

[Barrman]

My truck never had the stock alternator, so I never really paid attention to the post about adjusting them. Now, I am using a stock M715 alternator on my M35. I installed and wired up the 1967 GE Prestolite alternator yesterday.

The previous owner told me it over charged and just needed adjustment. I had everything but the exciter wire bolted in like it should be. Fired up the engine, checked voltage with a digital multimeter as 22.5. (One battery almost dead and the other more dead.) Aligator cliped the exciter wire to on and that thing kicked in. The idle speed dropped, it started to whine and 30.8 was the output voltage. I screwed the Allen head screw at the back all the way and all the way out. Nothing changed.

Does this mean the regulator is completely shot and need replacement? Is there another screw to adjust? Does anybody here have regulators for sale?

There is no hurry, I have another alternator to try and a complete truck to rebuild before I actually need it.

Thanks.

[brute4c]

There is but one adjustment screw...it is usually underneath a hex plug that is screwed into the alternator body...so if thats the one you turned, the unit has a problem...

[k8icu]

Wasn't your truck set up with a generator and voltage regulator originally?

[Barrman]

Yes it was Joe. I wasn't going to get into the truck stuff since I posted this in the Open forum on purpose. It applies to M715's.

But, since you asked. The truck has a positive cable from the battery to the starter. A smaller cable to the "on/off" switch and a wire from that switch to the distributor. A ground wire from a battery to the frame. Nothing else is hooked up. It has the floor mechanical push button for the starter so no wires needed. All other wires are either removed or not hooked up. I will be swapping cabs soon for a non rusted one. I am going to put a M35A2 wiring harness on it to get rid of the Douglas Connectors throughout. I like the internally regulated alternator idea better than the external regulator generator arrangement. Plus, 60 amps is always better than 25 amps when starting from scratch.

I ran the cable that is supposed to go between the M715 start switch and starter from the M35 starter to the alternator. Grounded the alternator to a lifter cover bolt near the alternator mount. Fired it up and touched the exciter wire which has a broken off Packard fitting on it to the positive lead to the alternator and took my readings right there at the alternator. I also had to swap the pulleys between the generator and alternator so the belts would work.

I was adjusting or at least turning a Hex head bolt that was pretty small, had no cover over it and was on the extreme rear of the alternator. After reading Jon's description, I might have been turning the wrong thing. But, I also think this is an odball alternator compared to all the other MV ones I have seen on other peoples M715's and M35's. I did pull it off of Pistolnut's totally stock winch 715 in my class. He said it had always over charged, so I knew about that going in. Just figured I could adjust it down. I will get a picture tonight or over the weekend.

[brute4c]

Take that hex out and look inside the hole and see if there is a thin slot straight blade screw head...if so, that is the adjustment and the hex is the plug to cover the hole.

I do know the M715 wiring goes like this...if it helps:

Positive, 24 volts, from battery TO starter switch on floor.
Output of alternator TO same post of starter switch as positive from battery.

Starter stud TO opposite side of start switch as above 2 wires.

Excite wire, through a splice or 2, TO on/off switch on dash.

Ignition power feed TO on/off switch on dash.


The wires at the on/off switch are:

2 wires from the alternator output/battery which provide the power to the on off switch.

1 wire TO the ignition feed and 1 wire TO the spider harness and the alternator excite circuit.

[Kaiserjeeps]

Tim, like Brute said the adjustment screw is under the protective allen head plug. A very small regular screw driver will do fine. Turn it very slow and only a little bit at a time. It is very sensitive. At least mine was. Good luck !

[brute4c]

I think they all are...a little goes a long, long way.

[k8icu]

Ok the reason I asked was that I thought that maybe you were trying to run the altinator with the generator wires and I was going to tell you that wont work, but since you've bypassed it it doesn't matter. Going with the A2 wiring harness will allow you to hook up the altinator properly, but you will have to add the ignition circute since the A2 truck was a diesel, but you knew that.

I just pulled my 151 manuals (since mill standard is mill standard) and they way Jon says is the way to hook it up. That should charge the batteries for you till you get it all redone. Yes also pull the hex bolt and turn the teeny tinny screw. If you have an allignment tool for electronics (non matalic) that would be better to use. Less chance of possible shorting out.

[Barrman]

OK, here we go. This picture is the alternator off of Pistolnut's M715 that I installed on the M35(R) on the right.

It was pumping out 30.5-33.5 volts if I increased the rpm. It turns out I was adjusting a screw that wasn't an adjustment screw. Thanks to the help from this morning, I found the right plug and the right screw. I couldn't get a screwdriver on it with the belts on too. So, I turned it a little, swung it back into position, put the belts back on and fired it up, repeat. I got it down to 29.3 at idle, but it would shoot back up into the 30's at rpm.

Then I swapped the pulleys and installed the one on the left in the picture which was also originally off of a M715. Notice they are two completely different designs.

The first try gave me 27.9 at idle and 27.9 at rpm. I left it alone until I get the entire truck wired and two batteries that actually hold a charge hooked to it. Here it is on the truck.

[adk4x4]

The alt on the right is the model that replaced the A1003 series alts. Leese still stocks replacement parts for the AMA series. I think they still use these in hummers.