Cadillac explains why they used positive ground for so long

[Chris Cummings]

From the January 1, 1928 issue of The Cadillac Service Man:

“Question:  A.C.O., New Haven, Conn. â€" Why is the positive terminal of the battery grounded on Cadillac and LaSalle cars?

Answer:  The positive terminal of the battery has always been grounded on Cadillac electrical systems.  The advantage is that with this arrangement the positive terminal of the battery is more easily replaced if it corrodes, and our experience has shown that the positive terminal usually corrodes first.”

There you have it from the factory.

Chris Cummings
CLC 20072

[Bob Hoffmann CLC#96]

Chris,
Thanks for posting it & making my day. Best laugh I've had in awhile. The fact that there were out of  step with the rest of GM makes it even more ridiculous .
Bob

[Chris Cummings]

Glad I could brighten your day, Bob!

Cheers.

[Doug Houston]

There's a lot more to this than corrosion of the positive terminal.  Even today, the positive battery terminal attracts corrosion more than the negative terminal Whether the positive terminal is grounded, or whether the negative is grounded, corrosion STILL is attracted to the + terminal.

before I explain my take on this, I'd call your attention to the number of car companies in the thirties that used positive grounded systems. Just from memory, here are a few: All Ford cars, Chrysler, DeSoto, Dodge, Plymouth, Graham,  Kaiser, Fraser, Packard, and of course, Cadillac and LaSalle.

Then, because my book with that chart is out of my reach, I'll draw on memory, with Auburn, Cord, Duesenberg, Hudson (and Terraplane)   There were quite a few more, but I hope that you get the idea. Matter of factly, General Motors was far and beyond in the minority in the polarity issue.

The tendency for corrosion is based on the same principle as polarity in a vacuum tube. Positive charges attract electrons, within the tube. Positive charges attract electrons, and corrosive action when positive charges are present. Thus, the positive battery terminal attracts corrosion. Remember, there is acidic vapor about the battery, as it's in a charging condition. there is also hydrogen gas coming off of the battery during charging, so don't get cute with sparks or flame near a lead-acid battery ANY TIME, just to be safe.

Now, why the controversy about polarity?  It was an on-going issue about whether distributor points failed from metal migration faster with one connection or without. My boss at one time was an authority in the industry on ignition.  One day, we had a few minutes to loaf, and we had him explain all this about polarity, and the issue was just that simple. Much as it was debated, the issue was never resolved. Several foreign cars had differing battery polarities, most of which used 12 volt systems.  When all of our domestic cars went to 12 jolts, did it ever matter/ Heck, no.

Look at Chevrolet with the 6 volt negative grounded systems. They had a reversing switch for the distributor points. It reversed the points every time the starter linkage was operated. Did it ever make any difference? Nope. I have a kit for that switch for my '41 Chevy, and it stays in the box, 

[Bob Hoffmann CLC#96]

Guys,
Doug is much more an electronic guy than I am. My points are that in MANY cases Cadillac was "out of step" with the other GM Divisions.
The ground issue.
No VIN tags on the "A" pillars.
The 5 digit group #'s in the Master Parts Books.
Not offering cowl AC until 1957. Also Olds.
Not offering electric wipers until 1959 ,also Olds, and having the ridiculous vacuum booster in the oil pan.
I'm sure there's more....
Bob

[Doug Houston]

I suppose that lots of things like that an be said about Cadillac.

Battery polarity meant very little, as I've already said. Nobody need be strung up for those differences. If anything, GM was out of step with the rest of the industry.

No VIN on the cowl? it was on the block (not especially easy to see!), and reasonably visible on the frame. My '41 Olds has a VIN tag on the firewall, right out in the open, and easy to remove and change.  The tag on my '41 Chevy is on the floor board, under the mat (carpet as I've changed it,) and almost impossible to read after all these years.

Until about 1960, Cadillac was the only division that owned its service parts. Now, whether or not, they were first to use the parts list system as  used by the rest of GM, I don't know.  I do know that it was a boon for me when I first got a Cadillac, because Cadillac still had a lot of service parts that I could buy for my '41-60S. That lasted until Cadillac scrapped their parts, and joined up with the rest of GMPD. I have a copy of the conversion book. It was a real mess to translate part groups to GMPD.

Air conditioning was something that had to be learned from the experiences of the air conditioners of 1941. Prior to that, it had been thought that it was simply a matter of refrigerating the interior of the car, and go away contented. There were lots of issues that were learned by Packard, Chrysler and GMC. It was never a matter to be simply picked up after WW II by the car companies.  If you drive a '41 Cadillac with A/C for a few hundred miles (and I have), there are a few things about the system that become annoying, such as not being able to turn it off if it gets a tad chilly. It goes on from there.

I've always suspected that GMC was in the sack with Trico, probably as it was with US Royal tires. DuPont owned a big percentage of US Royal, and probably a good chunk of Trico, as well. There HAD to something like that going on!!  Just remember that the DuPots owned a big slice of GM, too.

All GM divisions had their own engineering groups. That was a good thing, because they were in competition with each other, and some good things did happen as a result. One thing I never was able to figure out, was that Oldsmobile had the battery ground lead hooked right to the starter commutator end plate. There was no closer connection to the starter brushes (and its ground). Oldsmobile starters always cranked fast for that reason. Now, why in H--l didn't the other divisions, especially Cadillac ground the system at the commutator end plate of the starter??? I've done it on a few, (and soon all) of my cars, with a grounding stud. You should hear those engines crank!!

I suppose that we might have gone for some other kind of car, but I'm too old to want to change. I'm just lazy.

[Steve Passmore]

[quote author= Now, why in H--l didn't the other divisions, especially Cadillac ground the system at the commutator end plate of the starter??? I've done it on a few, (and soon all) of my cars, with a grounding stud. You should hear those engines crank!!
[/quote]

Thats interesting, could you post a picture of how you have done this?

[Doug Houston]

I found the picture of the Oldsmobioe starter grounding, but for why, I can't find the Cadillac pix. But, this will show how Olds did it, and how I did it to the Cadillac starters.

You remove the commutator end plate from your starter. Find a recess inside the plate, and drill a hole in the end plate for a 3/8" hex head bolt that will be in a good spot for the engine ground. Put a hex nut with locking washer  that will protrude long enough for the battery terminal to be bolted on, with another hex nut. Inside the plate, the head of the bolt should clear any interior pieces. The brushes connect to this plate, as well as the battery ground.  Reassemble the starter, and re-install on the engine.  Connect the battery ground cable to the new grounding stud. You'll never believe how fast the starter kicks over the engine. My 41-60S sounds like it has 12 volts. Other starters work good; some faster than others. 

There will be no need for any other  grounding to the block, as it's all right there on the starter. 

[Steve Passmore]

Many thanks for that.

[Paul Phillips]

Doug, this is a great idea. I am going to modify my spare now as a trial.  Looks like there is a vacant boss position on the end plate that can be tapped at least for a 5/16 stud.  It is least than a half inch from a brush ground point.

Paul

[Paul Ayres #5640]

Bob - Cadillac had Delco electric wipers in 1929 on the open cars.  They only lasted one year, and it was back to vacuum for 1930.  I suspect Doug was right:  Trico had a real "in" with GM.   Paul Ayres #5640

[The Tassie Devil(le)]

The "good" thing about Vacuum Wipers, and the only good thing about Vacuum Wipers is that you can regulate the speed of operation very minutely.

Electric ones are either 1, 2 or 3 speed, whereas Vacuum there are many speeds.   Nowdays with Intermittently controllable wipes, the speed is still the same, but at different intervals.

Bruce.

[bcroe]

Connecting the (negative) battery cable directly to the starter is a good
plan.  But you STILL need grounds from the battery or block, to the car
body.  Thats so the lights & everything else work, without trying to find
a path through your accelerator linkage or something else. 

Grounding 12V negative aids all the electronic devices, because now the
"electronic ground" can be the same as the car ground.  Bruce Roe 

[Classic]

When installing a bolt in the commutator end plate, I would use a brass or copper bolt with brass nuts rather than steel, for better electrical conductivity.  These should be readily available from your local starter/generator/alternator repair shop.  But be careful not to overtighten as they are not as strong as steel.

[Doug Houston]

Connecting the (negative) battery cable directly to the starter is a good
plan.  But you STILL need grounds from the battery or block, to the car
body.  Thats so the lights & everything else work, without trying to find
a path through your accelerator linkage or something else. 

OK< now let's do a little thinking here. Assume that the starter motor has a resistance of, say a few microhms. While cranking the engine, it draws around 175 amperes. If it's grounded at the drive housing, as it is normally, you could lose a volt or so just from the resistance of the starting motor mounts to the brushes......right?  NOW, let's reverse the direction that the battery supply flows through the starter.  and have virtually NO resistance to the brushes, as I've said. The 175 amperes no longer flow through the starting motor, whose resistance to the block is that few microhms. The car's electrical loads flow through the starter motor right to the block. What's a few microhms to as much as perhaps 50 amperes? Nothing. The body of the starting motor will never again carry the full cranking current. That's what you want.

The other grounding points are not disturbed when the ground is brought to the commutator end of the starter.

Oh, and be careful about the metal in the grounding bolt. Remember, you're probably connecting a copper or brass bolt to an aluminum alloy. Consult the electromotive metal series before you go using metals that may be too far down on it.