DLaz70OLDS98

The chassis service manual for my 1967 Cutlass Supreme indicates that the differential ratio code letters are stamped on the right rear inboard side of the axle housing tube. All I could come up with was the attached picture. I know it is a type P housing but I was trying to determine the gear ratio without pulling the cover. Can anyone help me figure this out or point me in the right direction. Thanks
Drew

oldspackrat

It will be on the tube part of the axle, not the center section. You will need some sandpaper probably, a good light & some luck. Others on here can tell you where the letters should be on the tube.

monzaz

Yes that is a Pontiac housing That is the date code for the rear casting WILL NOT tell you what ratio is in the housing or what the housing came with from the factory. You need to look on the axle tube driver side axle tube on the back side or being a Cutlass if it was truly the original rear will be marked on the passenger axle tube facing the back of the car. THE round axle tube is where you will find your 2 digit code between the spring perch and the cast center section. Good luck. Wire wheel sand paper etc will work best.

DLaz70OLDS98

Awesome. Thanks guys. I appreciate your help.

Octania

Also, this is a classic case of the "stamping" term confusion.

The photo is of raised characters which were CAST into the part when it was made.

After the gear ratio was known, the letter code was STAMPED- which means to strike a steel stamp with a hammer, creating a slight impression into the surface of the part.

A casting's raised ID characters are not "stamped" information.

You realize that you can ascertain the gear ratio simply by counting turns of driveshaft required to attain two full rear wheel turns, right? That is, two turns of one wheel [handy if rear end is not posi], one turn of both wheels [easy if it has posi], or any combination thereof...

But, what a great excuse to pull that cover, read the tooth count off the ring gear, and get the answer, and BONUS, fresh juice on the gears after an inspection.

DLaz70OLDS98

Octania
Very good point. I had climbed under the rear and had noticed these casting marks thinking it was the stamp, silly me. I had already determined the actual gear ratio by the above "test". However, I wanted to see if the ratio i determined matched the stamp code or if the gear ratio had been changed at some point.
I will get to ripping the cover off and changing the fluid out after I finish the front end work, body mounts and motor swap. Thanks for the info.

Fun71

The stamped code can be really difficult to see. Most times there is a layer of rust and /or greasy dirt that has to be removed before you can see the it, and you have to know WHERE to look in the first place. This is what the code looks like on the original 10 bolt from my 71. This rear has been cleaned and painted so the stamping is easy to see:

197110boltR2256opendiffcomp.jpg


This is what the stamped code looks like on a '68 O-Type that I have. This one had a layer of Southern California surface rust wire brushed off before the code was visible:

196812bolt342HDopendiffTLcode.jpg

DLaz70OLDS98

Awesome, thanks for the picture Kenneth.

Octania

Great pix of what to look for.
They are oten upside down, because the diff was upside down at the time they did that.
Much like the frame PN/letter code ID tag.

"a layer of Southern California surface rust..."

HA HA HA HA
that's a good one.

That is -so- NOT "a layer of rust"

In MI, you have zero chance of finding a lightly stamped ID like that, because the rust has eaten the metal. Great shots of what they used to look like though. One of these days I am going to write a facetious book on "numbers matching" and how to read ID stamps thru the rust.