David DeCan

Need some help identifying a Chevy 12 bolt rear end. It is supposed to be out of a 68-72 Chevelle. Want to swap in a 12 bolt for my O type.

Also would like to know if gears, carrier are original, as well as the gear ratio.

Below are some pics. There is also a video clip included in the attachments.

Thank you.
David

Qwik71442

Chevrolet 12 bolt

CW=3.31
04=April
17=day of month
B=Buffalo Plant

I believe this may be the housing stamp maybe others would know for sure. Count the ring and pinion to know the ratio for sure.

orange442

Look for numbers like 14 & 43 as an example and divide big by little to get ratio.

svnt442

I counted 43 teeth on the ring gear. If you have 13 on the pinion then I would suspect that it is an original gearset.
43/13=3.30769 (3.31)

David DeCan

That makes sense 43/13 for 3.31. But I don't k know how to ID the rear? What is it out of? Is it a 68-72 Chevelle, El Camino, Monte Carlo?

orange442

What is casting # and date code on the cast center section?

David DeCan

Do the gears look original GM? Seller is checking for casting numbers.

orange442

I am thinking aftermarket because CW is code for non-posi rear and this has posi and the gear is possibly newer as well, need numbers to determine any more as anything else is just a guess!

David DeCan

Just received these pics.

The long number reads: 3917124N. Thank you for your help all.

Just received post on Classic Olds saying CW on axle tube was a non-posi which would ID the carrier as aftermarket because this is obviously a posi. Can anyone confirm this?

What are the white painted on numbers on the ring gear. Anyway to know if these are aftermarket gears?

orange442

1968 housing C-6-8 date March, 6 1968. Now get any stamped #'s from the ring gear to determine gear ratio and possibly a brand on it.

monzaz

You all need to remember the likely hood your going to find ALL STOCK original rears anymore is LOW.... I personally have taken MANY MANY open rears and installed GM stock posi units into them for customers and just eBay builds. So.... BE HAPPY you got a posi as that is 300.00 extra easy.

Do not worry what the tube says unless your a 100 point resto car. and in this case... Your getting a freebee posi.

Knowing what it was removed from. YOU WILL never know if it was removed from a chevelle or El Camino as they used the same codes and rears

NOW Monte Carlo came later so its code will be RV RU (1971 1972 era) My SS Monte si RU which is open 3.31 But of course i made it posi.... ...Unless it is 1970 then it will be a C CW CF so 1970 had 3 letter suffix codes. Also in 1970 Monte chevelle and El camino shared rears - ALL A-body chevy

monzaz

Well the Posi and the gears are Original GM items. see the 45 white ink... stamp that is GM inspection stamp. some will have 46 44 etc. tHIS IS TO ADJUST THE pINION DEPTH 45 is the middle with NO adjustment required
less and subtract more and add to the pinion depth. In the GM fisher body etc manual...

David DeCan

OK. But here is the $100 question, before I drive 200 hundred miles.

Is it out of a 68-72 Chevelle/El Camino/Monte Carlo, thus assuring it will bolt in my 70 Cutlass?

Thank you!!!!!!!

orange442

Yes, 68 A-body for sure! All 68-72 A-body rears are the same as far as bolting in, yolk will be different length is only difference.

David DeCan

OK. Thank you. But how are you ID ing that it is out of A body?

David DeCan

Do not know what it was removed from.

I am told it was removed from a 67 Chevelle.

Being sold because axle tubes are too long causing tire clearance problems.

But I have not seen this...

monzaz

The date could be either 1969 or 1968...HArd to make out the number 8 or 9 and BOTH would be correct. The date on the ring will give you a better idea of the housing date... they should be kind of close.

The date of the ring gear and part number and tooth count will be on the edge of the ring and the head of the pinion OR on the machined back side of the ring and the head of the pinion.
Have fun playing. Jim
J D

orange442

From info I have looked at CW is code specific for A-body 12 bolt only.

garys 68&72

If you need a measurement to confirm the width, I have a 72 chevelle 10 bolt sitting in my garage. Should be the same width. Going into my 72 Olds.

David DeCan

Installing that Chevy 12 bolt in the Cutlass.

You will recall it is a 68 or 69.

Earlier in the post you mentioned that the gears and posi are original GM.

Question:
What gear oil and additive do I need? Is this correct:

GM #89021671 80W-90 Axle Lube
GM #1052358 GM Limited Slip Additive

Is this correct?

Lastly in looking at the pics--is that an Eaton Posi or other?

Thank you. David

Magna86

Yes those will be fine and its an Eaton type posi.

David DeCan

How many quarts of Axle lube and additive will it take. It is dry now. Thanks

Magna86

You use one bottle of additive and around 1 1/2-2qts if my memory is correct. You fill it from the fill hole on the side usually passenger side of pumpkin. Use a 3/8" drive ratchet to remove the plug.(may need an to use extension) Clean out the plug with a small screwdriver to makesure you get the ratchet in as far as possible so it bites and doesn't slip. Put the additive in first then fill it with gear oil until is drip out of the plug hole.

David DeCan

Spent the better part of a morning researching this gear oil question. It is a morass. All I am really looking for is quality product that is not going to tear up my Muncie and my Chevy 12 bolt. The amount written on GL 4 versus GL 5 as it relates to "yellow" metal deterioration is incredible.

This is what I am buying at Amazon:

GM #89021671 80W-90 Axle Lube GL4 23 oz/bottle
GM #1052358 GM Limited Slip Additive

Question: Can I use that same 80W-90 gear oil in the 1968 Muncie M20? No additive of course.

Question: Is AC/Delco the same as GM as it relates to gear oil?

Question: How many 23oz bottles of 80W-90 should I buy to fill both the Muncie and the Chevy 12 bolt? (If I am using the same product).

Thank you!!!!