I bought a 12 bolt the other week from some guy and he said it was from a 67 chevelle. I have the following numbers but they are not matching up. It had the spring perches cut off so I will have to weld on mine from my 10 bolt. I have a 67 malibu.

On the bottom front of center section:
left side is GM54 (not sure what this is)
right side is 3969278NF (guessing this is 70-72 chevelle)

On the bottom rear of center section:
left 0072 (not sure)
right 8230 (not sure)

On left rear of center section where axle tube goes in:
67890 (not sure)

On right axle tube:
CRW0318B1 (I think 0318 is march 18th, unsure of ratio??)

Hopefully somebody can help me determine what it is I have ...
Thanks in advance for any advice.

Lefty

http://www.chevellestuff.com/qd/generic_rear_axle_info.htm

http://www.chevellestuff.com/1970/rear_axle.htm

so according to the link it's from a 70 chevelle ?? And the CRW indicates 4.10 gears HD from LS6/454 ?? Does that mean it isn't a posi unit???

Yes ,it wasn't born with a posi but as it's 39 years old ,could be anything inside.
Did you read Dale's note on the (LS6/454)*:
* Engine RPO code and size following the rear axle ratio are taken from build sheets and/or Protect-O-Plates and may not reflect the only engines the rear axle codes came with. Where there are no RPO/engine information following the rear axle code only means I do not have build sheets and/or Protect-O-Plates to verify them.
Pull the cover and see what gears/carrier are actually in it.
Probably due for a lube change anyway.

It does have the red plastic tag by the filler hole that says "use limited slip dif lube only" ... does that indicate it is posi?

I can open it up tonight ... I am a bit of a newby .. What do I look for inside?
Do I count the teeth on the gears ... I believe there is posi pack inside is that correct?


I turned the yoke a little over 2.5 times to make the brake drum go around once ... What does that indicate?

open it up and count the teeth on the ring and pinion gears

cause a series-2 posi won't due you much good if you want a 3-or-4 series gear...... :)

Gears usually have the gear count on the side of the ring gear.
If it's still a 4.10 ,you would see 41/10 along with the P/N of the ring gear (3862526).
If it's a posi you can tell by the springs shown in the center of the carrier
http://img.photobucket.com/albums/v243/gtr1999/Differentials/yokeends.jpg

OK, It is a posi unit ... Identified by the springs as in the picture above.
The numbers on the side of the ring gear are as follows ...

2 GM 3862689 13 43 9 69

So what gear ratio does this relate to???

Thank you guys for all the great info by the way!! Really appreciate it!!

Lefty

I think I found my answer by searching around the site. It appears that it is a 3:31 gear ratio .... by this prior post.

big gear head
Apr 18th, 04, 11:21 PM
13 and 43 is a 3.31 gear, which means you have a 3 series differential. If the posi is a 3 series then it will work. The 3 series posi has the casting number EDB-30140 and the 4 series has the number EDB-30174. Too bad you don't have the pinion for that ring gear. There are a lot of people looking for the 3.31 gears. Nobody makes them new anymore.

Divide the large # by the small #. 43 divided by 13 = 3.307 So you have a 3.31 posi..

Yep ,3.31.
3862689 is the p/n of the 3.31 ring gear.
3862693 is the pinion gear and together they are the 3961405 gearset that a lot of people desire.
That posi was added with the gear change as it's now a 3 series carrier and not the 4 series that the 4.10 used.

Another Newbie question:

I would like to put this rear in the car soon .... The internals and gears all look clean ....

Being that it is old ...

Should I put new bearings in it? If so, how many are there??
Should I have the shims checked by a pro??
I was thinking on going to the "Ford Torino Big bearings" also. Do you agree??

What would be the best fluid to run?

Have no idea when it was redone but wouldn't hurt to have a rear end shop have a look.
Are the "Ford Torino Big bearings" your referring to the big pinion bearing?
If so,they don't fit a Chevy 12 bolt.
Now if your talking about axle bearings you would need to replace the housing ends.

Yes, I meant Axle bearings .... I heard they are the way to go. I was told they are much better then the C-Clip eliminators for street use.

Any idea what they would charge to go over this rear for me??

You might consider selling the 70 rear -it's wider than the 67 anyway -and get a housing with the Ford ends on it.
Might be cost effective also.
Check with Tom (http://www.chevelles.com/forums/member.php?u=10789) or Freddie (http://www.chevelles.com/forums/member.php?u=4191) ,both onsite,to see what a converted housing would cost.
They might also give you an idea on what your's might sell for.

I just sent Tom an email as you suggested.

Thank you for all your help.

how much would you be looking to get for it? i need to get something for the 402 because i know the 2.56 10 won't hold up. lol

email me at leftygolfguy@verizon.net .... Maybe we can work something out. I live in Harrisburg Pa so Maryland isn't to far of a drive.

I am still unsure what to do but make me a reasonable offer and we can go from there.

Thanks, Lefty

just a thought here... but if you are already going to pay to modify a rear end for the ford ends... You may as well modify THIS rear end as its already going to need welding done to it to put the spring perches back on....

It can be shortened when they weld on the ford ends, then you just order new axles the right length and away you go.

Just a thought...

Yeah ,but an unmolested 70 12 bolt might be worth it to someone that needs it.
They don't make them anymore.
I'm sure there's a few cut rears out there that he can use as he's modifying it anyway.
Maybe he's just going to try to help another Chevelle guy/gal get a decent unmodified 12 bolt - or not.

Yeah ,but an unmolested 70 12 bolt might be worth it to someone that needs it.
They don't make them anymore.
I'm sure there's a few cut rears out there that he can use as he's modifying it anyway.
Maybe he's just going to try to help another Chevelle guy/gal get a decent unmodified 12 bolt - or not.
Did you read the post, the spring pads are already cut off.

I was talking more about the tubes not being cut -yet ,but hack away.

I'm still trying to decide which way to go .... If I get a fair offer on it I would probably sell it to someone that needs an uncut 12 bolt. Then I could take the proceeds and add to it to purchase a new moser or currie rear the correct width.

If not, I will probably shorten it, install the ford ends, and new axles. I believe this option would cost me about a 700 bucks to have done.

What do you believe would be a fair asking price??

Yep ,3.31.
3862689 is the p/n of the 3.31 ring gear.
3862693 is the pinion gear and together they are the 3961405 gearset

"that a lot of people desire."


That posi was added with the gear change as it's now a 3 series carrier and not the 4 series that the 4.10 used.

Right now I have my 71 12 bolt apart and axles out, My car is a '70 so my rear was changed along the way. Correct rear, wrong year........OK I have a 3:31 and was thinking about going to a 3:73, what makes the 3:31 desireable? My only concern about the change is that in 3rd with 3:31 it will rev like 4th with the 3:73. Is the 3:31 valuable? Mine is in excellant condition.......Also what are the different series rears? Series 1, 2 ,3,4 ?

Thanks,
Roland in NY

Any guesses how many times 13 goes into 43?

Divide the large # by the small #. 43 divided by 13 = 3.307 So you have a 3.31 posi..


This many :D