Got a 65 wildcat and I'm thinking that I have a posi diff. Both wheels want to turn forward when you rotate one. No tag on the filler plug any more. Tell by a part # ? The 63 service manual says there is an X in a circle on the carrier flange. Any tips? Links?
In the 64 manual, it is identified by an x with a circle around it located on the bottom side of the carrier housing flange. Hope this helps, either way look for an X somewhere!
I also read that the Posi has a 3/4 inch pipe thread filler hole with a square head that you can put a wrench on. Non posi has a smaller 3/8 filler with a indented square that you would put a rachet into.
The way to tell is by what has been said is one way to determine if posi or not. The only exception is that the 3/4" square is the size of the wrench required to remove the fill plug. It is NOT a 3/4" pipe plug. It has it's own very fine threaded plug with a gasket. Very rare & hard to come by if one is needed. The 3/8" square that fits a 3/8" square ratchet into is an open rear.
Tom, doesn't the oil fill plug trick only work on '63-'65 cars? According to the Buick Master Chassis Parts Book 1940-1967, all Buicks from '39-'62 used the same square plug as the '63-'65 posi cars. It is group number 5.400 part number 1390882.
I honestly couldn't tell you that fact as I don't really know. I do know that I have '61 & '62 LeSabre cars that don't have posi & don't have the 3/4" square. These are open drive rears. Both the '57 Specials I have I haven't really looked. Now I will have to crawl under these two & find out. Tom T.
Here are some pictures of the ones I have, they are: 1957 Special 3.07 Non-posi 1957 Special 3.58 Non-posi 1961 Electra 225 3.23 Posi 1962 Wildcat 3.36 Non-posi 1965 Riviera 3.42 Posi
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