How do you verify the rear end date for an O type rear end?

 

What year do you have? 68-72, have a letter stamped on left side for the month, and number for the day, but no year stamped.

 

The rear end is in a 72 cutlass parts car. It is TM ratio code. Has 402227 casting number. It has the sealed bearing axle plate. Just trying to verify the year. Has the12 bolt cover.

 

TM AND sealed bearing with a 12 bolt cover sounds like a 70 12 bolt with 342 gears

 

The 8.5" corporate 10 bolt rears were used in 1971-1972 Cutlass vehicles. The rearend casting number you posted is for the 1970 O-Type rear, so someone swapped rears at some point.

 

Thanks for the input. Supercars unlimited noted in their rear end info that the early production 70 rear ends used the sealed axle bearing as opposed to the open axle bearing. Anyone else find this to be correct?

 

Seems I recall that a year or so ago someone here on the forum had posted pictures of a 1970 housing with sealed axle bearings. maybe search on that casting number and see if that thread turns up.

 

Anyone know what S A means on rear?
hopefully not 2:78 open

 

Codes are located in front pages of CSM.

 

My 1971 CSM demonstrates application 31-400 Exc. W-30, 2.73 gear ratio, 41:15 gear teeth differential.

 

so its a 2:73? open?

 

And, yes STD 8 1/2” w/ 10 bolt cover - NOT anti-spin.

 

Bummer,
came across a 71 Hardtop
black car in epoxy primer
new interior not installed yet
rebuilt 455 15k
thinking about getting it, I guess i would have to do the rear

 

Hello everyone! I’m trying to find the correct rear code and eventually the correct rear end for a 71 442 W30 4 speed. At some point the rear end in my car was swapped out for a 12 bolt posi. Any help would be appreciated. And a photo of how it should look too if possible. Thanks

 

Mjnorris
There were 3 ratios available from the factory for 71 W-30s. 3:23, 3:42 and 3:73. Will need some more info to narrow the possibilities.
- Air Cond W-30s were all auto/3:23
- Is your car a factory 3 or 4 core radiator without air cond? 3 core would indicate a 3:23 or 3:42. 4 core would indicate 3:73.
- Is your car an auto or 4 speed?
- 3:42 was the standard gear for 71 W-30s

Don W

 

Mr. shifty, we are getting close!. Factory 4 speed, no a/c, no power brakes and a 4 core radiator. It’s also a convertible if that helps. In the response please let me know if it’s a 10 or 12 bolt. Almost there. Thanks. Mjnorris

 

So with rhat info I would think a 3:73 would be correct. 10 bolt.

Don W

 

Thanks! Any ideas on any visible coding on the axel or housing?

 

3:73 for 71/72 W-30s are stamped TO on axle tube.

Don W

 

Your help is greatly appreciated! All the best Mr. swiftly

 

You're killin' me Smalls.

That gear ratio would be 3.73:1 and not 3:73.

 

Does that mean your daily driver is not 3.23 as written in you auto bio but 3:23:1...... just saying. Also can anyone post a picture of how the stamp on the axel would appear ?

 

lol

 

Does anybody have any pictures of what the axel stamp looks like. Looking to see who the TO stamp looks. Thanks.

 

Where did you get that? 3:23:1 means there are three gears.

 

Below are pictures of the O-Type rears in my inventory showing the code on the passengers side axle tube.

1968 "TL" code (3.42:1 ratio, open carrier, HD 31 spline axle shafts)





1970 "R2" code (2.56:1 ratio, open carrier)

 

Finally!!! Kenneth, thanks you. How hard will it be to find the correct rear end for my Olds? I guess I’m looking for a 10 bolt corporate rear end with the TO code stamped on the passenger side. 3:73 posi. Any and all help. Or should I just never mind and live with the 12 bolt. I just missin* a few original parts. Rear end, distributor fuel filter. Thanks to Kenneth and this site. Mark

 

Sorry, you said you were looking for the stamping for an O-Type rear. Your 1972 car would have a corporate 8.5" 10 bolt rear, not an O-Type as those were last used in 1970.

If you have a Chevy 12 bolt, that is a very strong and desirable rearend. Unless you were wanting to restore everything to show quality original, I see no reason to change it for a different rear. Having said that, assuming you could locate a correctly date coded 3.73 TO code rear, you would be able to sell the Chevy 12 bolt for a decent amount of money, likely enough to cover the cost of the TO code 10 bolt.

The corporate 8.5" 10 bolt code is in the same location but is different as it incorporates the GM division and the date along with the gear ratio designation.

This is the axle stamp on the 1971 8.5" corporate rearend from my convertible. The info I was able to get says:
R2 = 2.56:1 gear ratio, open carrier
0 = Year (?) still not 100% on that
068 = Julian date (68th day of the year)

 

Kenneth, this is the best no so far and thanks! I have a 71 W30 4speed. You wrote 72 in your findings. Does the info change? Mark

 

Sorry about the year difference, I saw that you posted the rear was in a 1972 parts car. Anyway, the stamping would be the same for 1971 and 1972.

 

Kenneth, the first "O" is actually an O and in between N and P, signifying Oldsmobile production. The fact it looks like a zero is likely just laziness on a factory working stamping the axle.

 

That is what I originally typed, but then I got to second guessing myself since the two characters looked like zeros. It is an Oldsmobile produced rearend as it has a block "O" on the forward facing areas where the axle tubes attach.

 

I am so glad those are stamped what appears to be upside down. For the life of me I couldn’t find my code 6S in the CSM, then I realized it was actually S9 (3.42:1 anti-spin), 🤣