Hi, I was wondering if I could take an open differential out and replace it with a posi differential to have a posi rearend. Is it possibly to do this and also is it cheaper? Thanks.

Yes, this is done all the time. You need to know how to check and reset the backlash before you get started. You also must have the right series posi for the gear ratio that you are running.

How exactly do you find the series?

Depends on which rear end you are working on. You go by the casting number and which gear ratio is on it. The 10 bolts are different and so is the 12 bolt. Which one do you have?

its a 10 bolt

The 8.2 10 bolt uses a 2 series differential for gear ratios below 2.73 and a 3 series for gear ratios from 3.08 to 5.13.

SSwannabe,
I just replaced my 307 in my 69 with an L-78 396 :D and will be following this post. Let me know how you make out cause I was thinking of doing SOMETHING with my open 10 bolt, either doing the change your speaking of or a complete 12 bolt rear end change over.

Does anyone think a 12 swap is necasary :confused: ? Im not gonna run it on the strip just cruise it and the ocasional burn out :rolleyes: , would a 10 bolt hold up? It seems like the easier swap. graemlins/thumbsup.gif

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Harry,
The 10 bolt may live behind your BB, but you won't be able to beat on it a lot. You didn't say if you have a 4 speed or automatic, but it will live behind an automatic much easier. If you think you need a 12 bolt I can build one for you.

BGH,
Sorry, It's behind a T400.After eating up all my budget (and a little more, hope the warden doesn't read this)On the engine,body and paint work, there's not much left but dreams for a 12 bolt this year.
:mad:
So that's why I was thinking of just swaping differential's, Got to be cheaper now,BUT ,,,,,,in the long run maybe not Huh??

What would one excpect to pay for having one built? Also What gearing would you suggest for my set up in a 69 Chevelle
396/375 hp L-78
286/296 Hydraulic cam
T 400
Again no race car here and not looking too either, just the occasional burn outs.

Right now cruising @ 50 MPH it pushes around 2000 RPM,
Seems kinda high to me???

Without trying to sound stuiped I NEVER messed with a rear and don't know much about the gear ratio numbers or ANYTHING.
If you could shed some light on this and these questions I'd be MOST grateful.

Thanks Man

If you could find a cheap, complete 10 bolt posi with a good gear ratio to install in your car for now, that would be fine. I would hate to see you sink $600 into gears and a posi for a 10 bolt and then toss it for a 12 bolt later. A good 12 bolt with new gears, posi, bearings, axles and other parts can run between $1000 and $1500, depending on how you want it built. I think you would be happy with a 3.42 gear for good performance and still be able to drive it on the highway.

Thanks man,
I still have the run at an old local junkyard that's closed down. They have alot of older stuff tucked away back there and I might go on the hunt for something this weekend...

I've heard that some El Camino's and certain year montes will bolt in to my 69 Chevelle with no modification.Do you happen to know the years and or models that would work for me?

If by chance I DO find a 12 bolt out there how do I tell if it's already a posi? I heard the old story that if you raise the wheels and turn them and they both spin in the same direction it's a posi......BUT......I also heard that wasn't always a true way to tell???

Is there a code number on the housing? and what about ID'ing the gear ratio, must the cover be removed for that?

Thnaks for ALL your help man graemlins/beers.gif

All Chevelle, El Camino and Malibu station wagon rear ends will fit up to '72, but the '64-'67 rear ends are 1 inch narrower. The only way to be sure if it has a posi is to take the cover off and look at it. Rust and other damage can cause both wheels to turn together like a posi.

Big Gear head,
Thanks for all your time anwsering my dumb questions.

Like I said I never messed with rears before and by taking off the cover and looking that would be telling me???? I don't know what i'm looking at :rolleyes: OK you can pick yourself off the floor and stop laughing at me ;)
Seriously though I couldn't tell a posi from an open rear by looking :confused:

Also I know there's at least 2 monte Carlo's 71 or 72 at the junkyard would they fit?

Here are some pictures for you to look at. Maybe you can get an idea of what to look for from them. http://community.webshots.com/album/55410292AnMJrE The Monte Carlo rear ends should bolt right in, and most of them that I have seen had the 12 bolt rear end. You need to go check them out!

Thanks Man........Come on Saturday!!! :D