The Chevy Positraction Story
A true story written 5/2013 rewritten 02/28/2016 unedited
This story is about determination, and what things are possible to do when you are under extreme pressure.
If you are not familiar with repairing or changing major parts on a car, you are probably better off not reading this story, as you will not have any appreciation of what I am talking about.
The term “Positraction” was terminology used by Chevrolet starting in 1958. It was a clutch system built into Chevrolets rear differential, so that if a rear wheel of the vehicle was slipping on ice or sand, the positraction clutch would transfer the power to the other wheel.
Then, one might ask exactly where is the rear differential located on a car? So let me explain.
Every car, truck or bus, has what is called a rear axle housing located under the rear of the vehicle. The axle housing is what the two rear wheels are attached to. On a GM car the differential, is a gear assembly located in the center of the axle housing. The gears in a differential allow a vehicle to go around a corner, by allowing one tire to turn more than another. For example, when making a right turn, the outer left side tire makes more revolutions than the inside right side tire, all accomplished by the differential.
The differential that does this on a GM vehicle are built into a heavy cast iron gear carrier assembly which is bolted into the center of the rear axle housing.
This cast iron carrier and differential gear assy, is sometimes referred to in the trade as a “Chuck”, the “Ring and Pinion”, or more commonly on a GM vehicle simply called the “Rear end”.
Once a chuck or rear end on a GM vehicle is installed into the rear axle housing, the right and left axle shafts are installed and the axle housing filled with 90 weight lubricant,
Which is a very heavy black oil.
Now, because a differential has so many gears and bearings, on occasion it wears out and needs to be replaced.
Automobiles that race, put a lot of pressure on the differential and sometimes it simply blows up, its gears break apart, and if that’s what happens, the rear wheels of the vehicle are no longer connected to the car’s engine and transmission, and the car needs to roll or be pushed off to the side to be towed away, to have the differential replaced.
Now, when a differential has to be changed, usually the mechanic that does it has the use of a hydraulic lift to raise the vehicle up to have easy access to it. This is important as on a GM car the differential, which is in a housing, is very heavy weighing from fifty to sixty pounds on an automobile. A truck or bus differential, weighs considerably more. So that’s why a special hydraulic lift is usually needed to remove them, they are heavy.
The thing that all GM differentials have in common is a ring of bolts holding them into the axle housing, a gasket between the differential and the axle housing that keeps the lubricating oil in, and a universal joint connecting the differential to the vehicles driveshaft.
All of these items, nuts, bolts and parts, need to be disconnected if one wants to remove a differential from an axle housing.
Then, after the nuts and bolts are removed, you need a method of catching the heavy black lubricating oil that pours out as soon as you unbolt the differential from the axle housing.
When Chevrolet invented the positraction differential. It was sold as an option, which meant not all cars from the factory had it, that meant it could be replaced with a standard non Positraction differential.
This story is all about my changing my 1959 Chevrolet differential, and how I did it without any help of a hydraulic lift and by using only two tools, a hammer and a screwdriver. I did it on the grassy esplanade right in the middle of the New Jersey Turnpike, working at night using the headlights of passing cars to see what I was doing.
In 1958, my parents were so happy that I was in college that they decided to buy me a reliable car. My father took me to Cooley Chevrolet in New Haven and he ordered a new 1959 Chevrolet. By the time the salesman and my father were finished talking, he ended up with a 1959 Chevrolet convertible that had a Positraction differential.
We asked what a positraction differential was and the salesman said “It’s totally experimental.” When it snows and one rear wheel spins, the car will automatically transfer the power to your other rear wheel and you won’t slide around, so my dad said OK and ordered it.
It was 1962, and I had just completed my eight weeks of basic training at Fort Dix New Jersey. My orders were to return to Fort Dix to serve six months as truck driver, serving in a motor pool.
I asked if I could return with my own car, and I was told I could but I would have to park it off base at someplace place called Wrightstown.
Now by 1962, I had really modified that 1959 Chevrolet quite a bit. It was quite the hot rod street racer. It looked so hot and intimidating, that it was common for other cars to pull up next to me wanting to race, so most of the time, I looked around, and if I didn’t think any police were in the area I would oblige them and race.
When I received my official orders to return to Fort Dix, I planned on driving my 1959 hot rod Chevrolet, and parking it in a Wrightstown auto storage yard.
I planned my trip very carefully, I knew it was only a three hour drive to Fort Dix New Jersey but since I didn’t want to be late for my new job, and I needed enough time to find the parking place in Wrightstown, I decided to leave the evening before I was due at Fort Dix.
I had it all planned out, I knew that I could eat and sleep at a motel that night and be in Wrightstown in the morning, to arrange for my parking.
The first part of the trip heading south to New Jersey went well enough until I hit the New Jersey Turnpike.
I was cruising along at the speed limit when all of a sudden there was a 1956 Chevrolet alongside of me gunning his engine. He shifted into second gear and floored it, which made his car jump up, and take off with a load roar. I had seen this maneuver a hundred times before, I knew this guy wanted to race.
I down shifted my car all the way to second gear and I floored it, then quickly shifting to third gear, and I started pulling away from that 1956 Chevy.
All of a sudden then there was a loud bang and my car shuddered and stopped accelerating.
I rolled into the grassy area in the center of the Jersey turnpike while the 1956 Chevy just kept on going.
I just sat there for a while until my nerves settled down, I looked at my watch. It was eleven PM in the evening and it was dark, only the headlights of passing cars and the turnpike light in the distance.
From the sound that I heard, I knew the Chevrolet “Positraction Differential” had blown up, I had to think.
I knew that if I walked to a service area and got a tow, I would get ripped off for a lot of money that I didn’t have, and here I was too far away from New Haven to call any friends to help, and if I did, what could they do? Then I got to worrying what would happen if I arrived late for duty at Fort Dix.
I knew that I couldn’t just leave the car, in the middle of the Turnpike, I ran the risk of having someone stealing parts off of it.
So I checked my wallet and I saw that I had a little over one hundred dollars in it, and that told me I could never afford to find a new or used positraction differential.
I thought about calling the Chevrolet agency but my car was way out of any warranty.
Then I got to thinking, to change the differential, was not that difficult a thing to do, especially if you had the right tools, I thought the job could be done in about three hours maximum. So then I thought I should look in the car’s trunk, I might have brought some tools with me.
I got out of the car and opened the trunk, I had a flashlight from my glove box so I used it look around the trunk, but besides from my duffle bag there was only a ball peen hammer and a medium size Craftsman screwdriver. I gave it some thought, there were no other tools so all my options were bad.
I got to thinking, and I took out the cars jack, and the spare tire, and then the lug wrench, as well as the hammer and Craftsman screwdriver. I then wedged the spare tire in front of the cars left front tire, thinking that if I jacked up the car, I didn’t want the car rolling forward.
I then loosened the two rear tires, with the tire iron, I was using the hub caps to hold the nuts. Then I jacked up the car, removed the rear tires and pushed them until they slid under the car. They fit under the left and right side of the axle housing, now if the car fell down off the jack it couldn’t roll forward.
I removed the brake drums, and brake shoes, then using the screwdriver like a chisel, I tapped each nut on the Axle retainers until I was able to turn them with my fingers. I had just enough light to see from the headlights of the passing cars on the turnpike.
Once the axle retainers were loose, I pulled each axle out about six inches, then
I slid under the car on the grass and using the screwdriver and hammer I bent away the locking tabs on the nuts holding the universal joint to the differential.
Once the universal joint was off, I was able to push the drive shaft out of the way, then I proceeded to loosen the nuts all around the differential carrier assembly again using my screw driver like a chisel, gently tapping it with the hammer. Then by prying with the screwdriver the differential assembly slid out of the axle housing, falling on to the ground with the black ninety weight oil pouring out all over everything and making a mess, it got all over my hands, pants and shirt, the smell of the oil was terrible.
I looked at my watch and it was already four in the morning, and not even one state police car had even stopped to see what I was doing.
I slid into the cars driver’s seat and tried to get some sleep, but the smell of the 90 weight oil was so overpowering, it was almost impossible to breathe.
At first light, a pickup truck pulled up right behind me. I didn’t know if he stopped to assist me or if he was thinking he could steal something from my car. But he was sure surprised to see me when I got out of the front seat.
I asked him if there was a junk yard in the area, where I could buy a used differential, and he said, “Yes” He said, there was a big junk yard about two exits back, so I asked him “If he could take me there, and again he said, “Yes,” but he said he was on his way to work, and we had to hurry up.
At the junk yard, they were just opening up when we arrived. The parts manager looked at me covered in black oil, like I was a crazy man.
I asked him if he had a used differential, for any 1955 to 1962 Chevrolet. Yes he said, they had one from a 1955 Chevrolet and the price was thirty five dollars, I said that I would take it and I gave him the money.
Then I told him what had happened and I asked him if by some chance he had a new differential gasket, so I could install his used part, and I also asked if I could buy some proper tools.
The junk yard guy asked me why I needed the tools, I told him I needed them to install the differential. He said, “How in the hell did you get the differential out if you don’t have any tools so I told him how I did it.
By now several more employees had shown up and they were looking at my old differential which I had carried in. I told them all that I had removed the differential with only a hammer and screwdriver.
“Are you bullshitting us?” the parts man said, now everyone in the junk yard was looking and laughing at me, but they could clearly see I was covered in the black grease.
“Where in the hell are you doing the job, the parts guy asked? “Up on the center of the turnpike” I replied.
The guy with the pickup truck that brought me, was starting to get antsy, and said he needed to go to work.
I could see the junk yard guy, didn’t believe I had taken the car apart with only a screwdriver and hammer. He said to one of the other guys, “Do any of you guys believe this shit. Then he then said to the guy with the pickup, “You can take off, I’ll bring him back to his car.”
I thanked the guy with the pickup for the ride and he left. I told the junkyard manager that I was afraid the pickup truck guy might try and steal something from my car.
He quickly went to the metal shelving behind him, and he grabbed several wrenches a new gasket and a big can of 90 weight oil.
I asked him how much all the stuff was going to cost, as I only had sixty five dollars left. He said, “Don’t worry about it,” and we got into his pickup truck and drove back up to the turnpike. My car was still there and no one had touched anything.
The Junkyard guy bent over and looked under my car. “God Damn” He said, you really did it, he had a newspaper in the cab of his truck and I used a few pages to wipe out the broken pieces of gears that were inside of the axle housing, and I laid the rest of the paper on the puddle of grease on the ground.
I saved a few pages of paper to fold into a funnel. I put on the new differential gasket on the axle housing, and with help from the junk yard guy we lifted and slid the heavy new differential in place.
With the wrenches the junk yard guy had brought, it was now easy to tighten all the nuts on the differential and the universal joint. And in less than an hour I had it all together.
I rolled up some newspaper like a funnel, poured his can of the 90 weight oil into a plastic coffee cup he had in his truck, and slowly, cup at a time, I filled up the differential with 90 weight oil.
The junk yard guy said, “I got to get back to the yard”. He gave me his business card, I thanked him for the tools and oil, and he took off. I put the axles back in and then the brakes and the brake drums and then the tires. I lowered the car, and put the spare back in the trunk.
When I finally got to the storage lot at Wrightstown, I went into their bathroom, and washed up with their soap and I changed into my military uniform. I left the oily shirt and pants in the trash in the bathroom.They called a Fort Dix Taxi cab for me, I was right on time, and it was just like nothing had ever happened.