# Rear end identification help



## Jstreet (Mar 9, 2009)

Ok my rear end was changed out at some point in time and I have not been able to get a proper ID on mine to know the gearing/posi/etc. So I'm hoping everyone can help. 

It's 12 bolt and has some yellow markings on the rear plate that appear to be from a junk yard. It is marked 69 442. Presumably from a 1969 olds 442. I don't know their ratios but I will do a search on it. There is one U-shaped cast on the left side of the pumpkin but I cant find any other markings anywhere on the thing.

When I jack the rear and turn the right wheel, the left turns in the opposite direction. (so, not posi, right?) How do I determine the gear ratio? Can I count the number of turs right v/ left?

The bolt which would hold the Indicator tab is broken off.

Thanks, J


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## 05GTO (Oct 6, 2004)

Here is some information on olds 12 bolts;

OLDSmobility.com - The 1967 Oldsmobile Cutlass and 442 Resource - 1967 Oldsmobile Differential/Rearend Identification and Ratios


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## Jstreet (Mar 9, 2009)

That site helps . Thanks. Apparrently, I have the type O-type. Looks like I will have to jack the back end, put the trans in neutral, and spin the driveshaft while counting wheel revolutions to determine the ratio if I cant find the marking on the inboard axle tube. Super. thanks


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## Jstreet (Mar 9, 2009)

My marking was on the passenger side outboard axle tube and read SE. Turns out it's an O-type 69 olds 12-bolt 3.23 ratio (same ratio as my original) with 42-13 teeth non posi. Thanks for the link 05GTO. 

From your link, I downloaded a really cool RPM calculator. It computes wheel size, aspect ratio, rear dif, transmission, and tire size to give engine RPMs from 10-150 mph. A great tool to play with if you're thinking about changing wheels, tires or any of the above variables. here's a direct link

Download Page for RPM Calculator

J


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## Jstreet (Mar 9, 2009)

*New Question I'm puzzled.*

OK. According to the markings/ID on the axle tube, the gearing is supposed to be 3.23. I read on another website that you can manually check it using this method:

Determining Gear Ratio

You will have to put the rear up on jackstands, put the transmission in neutral. Make sure that the car is quite stable, get under the car, and TURN THE DRIVESHAFT. Count the number of turns of the driveshaft it takes to turn one wheel one time. If you turn a wheel, instead of turning the driveshaft, you will only turn the other wheel (not the driveshaft). 

It also works better (more accurate) if you turn the driveshaft enough times to turn one wheel ten times, and count the number of times you turn the driveshaft. This is because it may be difficult to tell if the driveshaft goes around, say, 2.56 or 2.78 times for one turn of a tire. But if you turn the driveshaft enough times to turn a wheel ten times, you will have 25.6, or 27.8, or 41.1 (or whatever) turns of the driveshaft. Then just divide by ten to get the ratio of the rear. 

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I used this method and turned enough to to make the wheel go around 10 times. I got 16.25 turns of the driveshaft each of the three times I tried it. According to the directions, I have a 1.62 rear end. That can't be right. Am I missing something?


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## Jstreet (Mar 9, 2009)

*Nevermind*

After doing some additional searching, it seems this method is effective for posi ends only. The fella forgot to mention on open diffs you have to multiply that x2. so 1.62 x 2= 3.24.........it's 3.23 then for sure.


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