Input on differential

[rwg65]

Okay guys need a little input. I've had my car about a year now and finally got it streetable. Had to fix a bunch of things that previous owner really messed up. He was not a mechanic. The speedometer is off by about 10mph which I attribute mostly to tire size. He put 235/60 14's on it which are a little over 2 inches smaller than tires that came on the car. Any how I started wire brushing rear axle to find gear ratio and found ca 1113b. After finding the casting number it turns out I have a 68 chevelle rearend under my car and it looks like its been there for 40 years. My question is how does this 3.08 rearend compare to a 65 gs rearend pros and cons? I have a new auburn pos unit and 3.23 gear that came with car. Would it be wise to put this in or should I start looking for a 65 third member? Thanks for input guys.

Bob

[Brian]

Can you get some pictures of the rear that is in the car so we can help you make absolutely for sure it isn't the original rear end?

[rwg65]

Brian, I have the casting number and axle number showing it is a chevelle rearend. The ca is 3.08 ratio, the 1113 is for november 13th and the b is for buffalo. Some time ago someone changed out the whole third member on this car. I would just like to know how it compares to the original 65 rearend. Is it better, worse or so-so? Is it worth putting this auburn pos I have in it or should I look for something else? By the way the casting number shows it to be a 68 rearend.

Thanks Bob

[Brian]

There were two different Chevy rear ends in 68--the 10 bolt and 12 bolt.  The 12 bolt came in the 396 cars and in the station wagons, the 10 bolt was in most everything else.  Count the number of bolts holding the cover on.  If it is the 12 bolt chevy, it is better than the GS rear end, if it is a 10 bolt, it is not as good as the GS rear end (GS rear end had specially hardened gears and larger axle bearings).

[WkillGS]

Bob, what is the pn for the Auburn posi you have?
Auburn lists a 5420108 for the Chevy 8.2, and a pn 5420113 for the BOP 8.2 rear.
I don't know if they are interchangeable, but Chevy has c-clips to hold the axles in, BOP uses the retainer plate.
Spline count is different on the pinion gears, and both appear to use the same bearings.

Great differential info over at http://www.jdrace.com/
Jim Monzaz is a very knowledgeable guy....

[rwg65]

Yup Walt, I signed up on the jdrace site just waiting for the email so I can start posting and ask him some questions. Can't find any part number on it. I don't know if he bought it for a buick or not, I presume he did because nobody had cleaned the axle to look for numbers in a very long time.

Bob