Since I currently am not able to enlarge pics so I can't see Mark's chart, I'll assume it shows 3.07 or 3.31 as being the choices because that would be the two closest ones for what you have in 65 in a 12 bolt.

I also can not read the chart; as it opens only to about 1 inch and if I try to enlarge it just blurs.

I am not sure the original engine was a 300 hp 327 but it did have that decal on the air cleaner, but it is also not the original Air cleaner. I rebuilt a 327 in it now that would be around 300 -325 hp. It would be nice to get a copy of that chart.

I am rebuilding the trans and trying to decide what drive gear tooth number I should put in the tranny t400. Was hoping to get some easy info but as usual I will have to get it back on the hoist which my kids always seem to have tied up hahaha. Not having great luck finding diff code numbers but will have to get more serious. before getting the possibility of the 3.31 gear ratio I was thinking of a 9 tooth drive gear but now I will go back to the speedo calculator and check for the 3.31

Thanks for the help

That is interesting. In the 70's my friend had a 65 Impala SS 327/250 Powerglide with a 12 bolt posi and when we stripped that car it was a 3:31.

Have you tried looking for the code that's stamped into the differential?

If I recall, it should be stamped on the passenger tube, about 2 or 3" from the center carrier. It should be on the forward part of the tube, but may be up a bit. The letters are about 1/4" high, you may need to take a wire brush to the tube to see them.

Once you get the code, we can look up the ratio for you.

Or, pop the differential cover off and count the teeth on the ring & pinion. I'm sure you could use a change of gear oil in the diff.

I have yet to see one with no numbers stamped on it but some of them have been really tough to find, it took a lot of wire brushing and scraping.

Well with seeing the chart for the Pontiac engine and power trains I was sure that this car would have the 3.31 diff so I went out and spun tires. But low and behold it appears that I have a 3.07 after being turned as accurately as possible. The driveshaft only turns about 1 inch past the centerline on the last turn looking like total turns were about 3.10. Of course there is a little play but I tried to use it up before the test. I guess its time to just pull the cover and confirm. Enough procrastination hahaha

71 Ventura posted a photo of codes on diff see his recent post.

Checked one of my oldest books and this is 1958 to '68 Pontiac which was effective November, 1967 and this was the only code sheet in there, 1966 but should be the same.

 

-- Edited by 67Poncho on Wednesday 30th of January 2019 08:16:55 PM