Last night I picked up a GTO 10 bolt axle assembly to replace the O-type on my '68. Its a 3.55 limited slip to replace my 2.56 open with a leaking wheel cylinder and essentially no brake shoes left. It also happens to have the "N" nodular iron case, if it matters. Seems to be perfect timing for the install.

What am I going to run into for issues? I understand I'll likely need a hybrid U-joint. Will it require adjustable upper control arms to correct the pinion angle? I plan to box the lower trailing arms while they're off.

 

Its a 9795084 casting. Specs out as a '69 Ram Air IV diff.

 

From what I know and my experience, it should be a direct fit other than the u-joint.

 

I don't know, but would a Pancho guy pay top dollar for this? Might allow you to get an O-type built as you want using your current drive shaft. Maybe even come out ahead

 

My brother-in-law has a 68 GTO and the original 10 bolt rear is a cone type posi with a split case (10 long bolts hold the two halves together). The O-Type and later 8.5" 10 bolts are stronger rears but his original has held up behind a hopped-up big block, a 4 speed transmission, and a crazy driver, most likely because his car was always traction limited. Just wanted to let you know in case you intended to use this rear on a track car or such that it is not the strongest option out there, but should be fine for a street car.

 

This will always be a street car. I have an MGB track car - a serious go-cart. Since the axle is a '69, I think the U-joint actually fits properly. The axle is already in place. I spent the day changing oil, cleaning and painting, and doing the swap. Now I just need to install new brakes (wheel cylinders and steel lines already in) and the driveshaft. Napa says both diffs take the same U-joint, so I bought some heavy duty versions and will put those in last.
In the mean time, the O-type will be in storage in case I can break this one, and another 2.56 GTO 10 bolt came free with this one.

 

Wow, you're gonna have as many rearends as I do. I have these behind the house and the one under the car:

12%20bolt%20lineup_zpsmakqre1v.jpg

 

nodular rears are worth too much not to go back in a car they where meant to be in

I dont know about Ram IV stuff..id think it would be a 3.90 or 4.33..

ram air yes..IV maybe...

id do a little more research.sell it and take that money and buy a chevelle 12 bolt...just an idea.

whats the axle code? the casting number doesnt mean ram iv..its the code stamped on the axle that has the real value..youre on the right track, dont get me wrong...but there where 3.08 nodular rears..it was a heavy duty option too...just needs more investigation...it can be a $2g+ rear...

 

One can never have too many spare rearends with different gear ratios ready to drop in or cores for rebuild. :-) I'd research the rearend to makesure it isnt a high demand rear for a Pontiac guy like a TO rearend is for us.

 

Ram Air IV had 3:90's as std. in '69.

 

Where is the axle code? This thing was pretty terribly pitted, removed from a ram air IV, as I saw the car it came out of. As we know, GM is great about offering many gear ratio options, as evidenced by the Cutlass range of 2.56 - 4.56 if I'm not mistaken. Any gear set can be ordered with any car.
This was a 100% direct bolt-in.
The only way this car could have been more gutless would be to put the 2 speed auto back in it. I was immediately able to spin a donut in my shop parking lot. Wooohoooo!
Cosmetically, this is a $500 diff like what I paid for it. No more or the GTO guru I bought it from wouldn't have let it go so cheap. Plus I made a great contact for many other parts I'll be hunting for soon. Its amazing how many Cutlass parts are used on GTOs...

 

The performance variants were usually limited to certain gears that would work with an engine due to it's cam etc. I believe that the choices for the RAIV were the aforementioned 3:90's, 4:33's, and 3:55's. It's the same with '69 W31's for example, 3:42's, 3:91's or 4:33's, with 4:66's being a dealer installed option.

 

All I can say is that the switch from a 2.56 to a 3.55 posi is as good as I had hoped. The car is now "sporty" enough to light up the tires at will.