Can anyone help me decode my 1966 rear end. The two letter code was found on the passenger side axle housing facing the back of the car. It looks like it was upside down and appeared to be either IS or SI. This car is a 66 f85 330 with a jetaway all original and I know that the rear end is original to the car. Does anyone know what gears this car has also I believe it is a open axle but I never checked.

 

I believe the Diff casting # is 1375889

 

Axle codes are in the Chassis Service Manual and you can find that at Wild About Cars.

Wild About Cars. http://wildaboutcars.com. An information supersource, especially Oldsmobile. More Olds content than anywhere else on the internet and continuing to grow.
You'll find Chassis Service Manuals, Product Information Manuals (AKA Assembly Manuals), Inspector's Manuals, and other documents that will contain this and much much more.
Dealer Brochures, magazine ads and articles, and a home page for you online.

 

sorry wmachine I have to wait another week until my chassis manual arrives. Is there any chance you can check yours if you have time.

 

It looks like the code is Def SI.

 

As Wmachine said you can register at that site for free and view an electronic version of the chassis manual.

 

355, I'm surprised.
I went to http://wildaboutcarsonline.com/membe...ctions_0-1.pdf
Looked in the service manual, SI says 355.
Great site for info!!

 

66LUVR Thanks I will register. I never thought It would be 3.55 I figured 2.73 maybe 3.08. Is it rear to have that kind of gear. I had those in my 442 and it was an option I believe. Must say the 66 F85 is pretty quick.

 

Man this makes me want to go look at mine now.

 

Man this car is begging me to put in a 4 speed. What you boys think. The servo cover on the Jetaway is stamped 67 instead of 66 so I am thinking either the tranny was replaced or servo cover at some time.

 

I thought it was numbers matching but the servo cover has me freaked out now. I think I can use this excuse to justify the 4 speed conversion.