Technical how to determine rear diff gearing

Will someone please edumicate me on this. This is a chance that the differential in my 57 for wagon might have been replaced at some point in time. She came from the factory with 3.56 gears and I just want to make sure that is what I have.

If I remember right, I would mark the drive shaft and then rotate it one full turn. All the while have a helper count the revolutions of the p*** side tire. I think there is a wheel diameter that figures in this some where as well. She is running stock 14" rims. Is this correct?

Mike

 

Jack up only one rear tire. Mark your drive shaft/pinion and the rear tire. With car in neutral, rotate the rear tire 10 times, counting the number of times the pinion rotates. Divide your pinion count by 5 [ not 10]. If you have a 3.56, you should get about 17-2/3 revolutions of the pinion.

[Edit to correct - I misremembered about the spider gears doubling the ratio.]

 

No no no...
LOL

Jack up one rear wheel.
***uming no posi.
Both, if you have posi.
Chock the front tires, put the car in neutral.
Manually turn the drive shaft until the wheel has turned one revolution. At the same time, take note of how many times you rotated the drive shaft.
Three and a half times would indicate you've got your 3.56.

 

Mark is absolutely correct.

 

No No No

 

@1930artdeco
Don't take me too seriously this evening.
I defer to Mark. (Moriarity)
and stand detected infected and corrected.

 

What about turning the tire 2.5 times. I ***ume this will work with my auto just like a manual. Thank you all I will test it out this weekend.

 

why say that when Moriarty has already told you the exact correct thing to do?

 

The way I do it.
Mark the pinion, mark both tires to a reference point.
Turn both tires together, one revolution while counting turns on the pinion.
This isn't rocket science.
Bill

 

Well, probably should change the differential oil. May as well pop the cover and get it off the ring gear.
Two birds with one stone.

Edit: thinking about it, might be a drop out, may not want to go that route.

 

Mark's right, the rest of you need to check your medications

 

Hello,

After countless hours of laying on the cold concrete backyard outside area, I learned a thing or two. My brother and I wanted to be the fastest and quickest car in the A/Stock car cl*** at Lion’s Dragstrip. We started with the standard rear gears that came from the factory, 3:78 but the dealer supplied a Positraction 4:11 set to make the deal for purchase. The 4:11 Positraction gears were outstanding. Street performance was tops, the dragstrip times were compe***ive and a few trophies came our way.

But, as the year(s) rolled on, the compe***ion got better and extra stock items were necessary. Now, the top racers were using 4:56 Positraction gears. So, my brother had enough money to buy a complete 4:56 third member for the exchange.

The 4:11 seemed good for daily driving to school and work. But the 4:56 gearing was setting the top times and faster E.T. in the cl*** and for us. It also made the daily driving to school and work a tightly wound motor at each stop sign or light. There were no long distance cruises on our agenda like going to Santa Barbara or down to San Diego as a daily/weekend drive. It was a little too much being in the Impala.

Jnaki

So, I was designated to be the third member exchange guy as my early teen participation. I exchanged the 4:11 for the 4:56 unit on Thursday after school. Sometimes lasting past dinner or studying times.

Friday, my brother has his school and Friday night teen activity. Saturday was the all day/night races until we were the winners or eliminated in one of the rounds.

Then, on Sunday, I reversed the whole process for the next week’s activities. As the week progressed, on Thursday or Friday afternoon/night, I did the whole process over again. I actually had the aroma of the dead fish, Positraction oil built into my fingers after each exchange. Not good…

Was all of that worth the effort? Yes. When I was in the throes of racing the Impala, I set the best time of 14.68 E.T. My brother set the top time in a fast 98 mph in the quarter mile. It was usually a half second or 8 mph less for the 4.11 gearing. So, yes, worth every minute in the exchanges. But, I learned to count the teeth to make sure if, I was not falling asleep during the final installation, each time.

Note: When we installed the C&O Stick Hydro, the 4:56 gears got me out in front 99% of the time and the power we had usually kept me there to the win column. But, for the long distance cruises (in my Impala,) my friend and I created, we used his 3:78 gears and he ran my 4:11 gears. The 4:56 gears were sitting in my backyard garage waiting its turn for a "Big Encounter" on any given Saturday or dark street, late at night. YRMV

These days, here is something that is simple on any laptop access.
https://****erparts.com/calculators/gear-ratio-calculator

 

If it’s a non traction aided differential then you need two people in sync to do it your way.

 

..Not the most fun way to get that aroma on your fingers!

 

I'm always amazed at how confusing a differential can be to some folks.

 

Manyolcars, I was being a smart***, the emojis did not transfer over from the phone to the website. I will follow his instructions and verify the gearing.

 

I just read the tag.

 

divide the number of teeth on the ring gear by the number of teeth on the pinion

 

HA-HA-HA-HA......this is why I tune in nearly everyday !!!
6sally6

 

If it was easy, women and children would be doing it!

 

You must have really short arms.
I can reach and turn both tires evenly on every car I have ever done.
Bill

 

Ok this is way easier then turning one side two turns, you win.

 

And watch the drive shaft while knowing how many revolutions the tires were making and the shaft?
Giraffe neck comes to mind
I’m just having fun!

 

There’s alway’s math. RPM vs speed per tire diameter.

 

Rocket surgery, Bill, rocket surgery. No wonder you're confused

 

Well, I just did what Moriarity said to do. I marked the tire at 12 o clock and the drive shaft at 9 o clock. Rotated the tire two complete revolutions and the drive shaft went around 3 times. Giver or take a 1/4". So by his method I have 3.00 gears in the differential. To me that is awesome as she will be very derivable on the freeway and get more than 17 MPG from a 312/auto. Thank you all again.